Citizen's Guide to Colorado Climate Change

Citizen’s Guide to Colorado Climate Change

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Habitat Changes in climate affect everything in Colorado in some way. Lower river levels are likely to have an impact on water quality, aquatic habitat, recreation and agriculture. Higher temperatures and earlier springtimes may result in more fires, changing forests and grasslands, and opportunities for invasive species.

Water Supply

Recreation

Streamflows

Precipitation

Fire

Ecosystems Invasive Species 2

Colorado Foundation for Water Education Citizen’s Guide to Colorado Climate Change

Water Quality

Agriculture

Air Quality

Climate Temperature and precipitation, along with humidity, wind and sunlight, are the key climate elements that affect our crops, our comfort and our communities.

Energy

Citizen’s Guide to Colorado Climate Change Colorado Foundation for Water Education

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What do we know about weather in Colorado?

It’s always changing.

Rains while the sun is still shining.

Snows somewhere just about any time of year.

Lets the Broncos play on a January 60 degree day.

Freezes March heifers cold in their tracks.

Rips Big Thompson canyon out in August, spawns a Limon twister.

What do we know about climate in Colorado?

It’s Up and Down.

Like mountains and plains, like a hydrograph.

Dry spells. Wet spells.

Longer dry spells. Longer wet spells.

Any year you can go from desert to tundra and never leave the state.

What grows or doesn’t always depends on it.

What do we know about climate change?

Temperatures are increasing.

You never used to need a swamp cooler.

What we burn and emit seems to have something to do with it.

There might be wetter wets and drier dries.

There might be fewer skiing days, longer growing days.

It might be different than any scientist or government can make of it.

What do we know about us?

We’ve always been water short with an attitude.

Never enough we can do something about.

A cure for altitude sickness.

Preserve, conserve, come to water all who thirst.

Ante up the wherewithal.

Embrace creative uncertainty.

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Colorado Foundation for Water Education

The eighth in the Citizen’s Guide series focuses on…

what we know and don’t know about climate change and its impact on Colorado’s enduring legacy, its water future. What might Colorado look and feel like as temperatures rise and growing , skiing and rafting seasons shift?

An enduring legacy of Colorado is that Coloradans have always been good at adapting to a variable and changing water supply. The ancestral Puebloans of Mesa Verde between 750 and 1280 A.D., the Hispano settlers into the San Luis Valley beginning in 1852, the miners and farmers of the 1859-60 gold rush years, and the cities that followed all built ditches and reservoirs because they had to capture the snowmelt and the sudden storm runoff to survive and serve a growing population.

The early 21st century drought teaches us once again that nature rules. So does the law. A state that must deliver approximately two-thirds of its water downstream to satisfy interstate legal obligations must be highly attuned to conserving and using the other one-third as well as it can. We have nearly 2,000 reservoirs in Colorado, large and small, to store water in the time of plenty for the time of want. In a single severe drought year of 2002, when our rivers and tributary groundwater aquifers produced one-fourth of our annual 16 million acre feet of water, we released 6 million acre feet of stored water to meet our water use and environmental needs, bringing us to within a half million acre feet of exhausting our stored water.

Currently, there are 4.6 million people in Colorado, with 2.6 million more expected by the year 2030. The citizen water roundtable process is calling for a 50-year plan for Colorado’s water future.

Now we learn from our climate scientists—among the best in the world are right here in Colorado—that “wetter wets” and “drier dries” will likely mark our future even more than our past. The mathematical grid boxes of the existing climate models map a flat world. Flat is not Colorado.

We cannot afford the risk of doing nothing. In addition to the historical cycles of flood and drought, we may be facing an overall reduction in total water supply over what we historically planned for and depended upon. “Do we care?” has never been a question for Coloradans. “How we might prepare?” That’s the question we’ve always been interested in. Taking the calculated risk in the face of an uncertain water future is a most fundamental characteristic of Coloradans.

Citizen’s Guide to Colorado Climate Change Foreword by Greg Hobbs Colorado Foundation for Water Education

Citizen’s Guide Guide to to Colorado Colorado Climate Climate Change Change Citizen’s

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And strong opinions.

And multiple viewpoints.

Is climate change occurring? Not everyone agrees.

We cannot possibly verify what will or won’t happen tomorrow or in 2100. What we can do is look over the landscape of the past and quantify what’s seen.

To present a range of contemporary climate change information in this Guide, the Foundation turned to people recognized in Colorado—and around the world—for their roles in research, modeling and education. Their work resonates with policy discussion topics. For example, the debate about fossil fuel use and its effects has a markedly political cast.

The Foundation, whose role is education, does not take an advocacy or political stance.

We hope the Guide underscores the reality that Colorado’s water supply, as always, involves risk and uncertainty and requires careful planning.

In fewer than 50 pages, the authors write about the overarching themes and findings of their specialties.

They include references for climate change studies, presentations, books and Web pages.

The authors each approach climate from slightly different directions. For instance, Brad Udall, who directs the Western Water Assessment program, discusses the Rocky Mountains from the standpoint of the challenges they pose for computer modelers. State Climatologist Nolan Doesken talks about the same topography, but from the perspective of how it affects climate. And climatologist and researcher Roger Pielke, Sr., provides an alternative viewpoint, that there’s more than carbon dioxide involved in climate change. Forest research scientist Linda Joyce explains how species adjust according to elevation and climate.

In presenting the authors’ assorted viewpoints, we take to heart the comment of Foundation Board Member John Porter.

The retired director of the Dolores Water Conservancy District, Porter is a cautious man. He carefully considered the Guide’s content and the reactions climate change discussions evoke.

Said Porter: “It behooves us to be prudent stewards and mitigate our negative effect in a manner that is efficient, cost effective and environmentally friendly.”

Citizen’s Guide to Colorado Climate Change Introduction by Lori Ozzello, Editor

Colorado Foundation for Water Education

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Colorado Foundation for Water Education

Colorado Foundation for Water Education

Citizen’s Guide to Colorado Climate Change Foreword Greg Hobbs................................................................................................................1 Introduction Lori Ozzello............................................................................................................2 Climate Nolan Doesken The Most Important Natural Resource...................................................................................4 Colorado Weather Extremes.................................................................................................12 Global Climate Models Brad Udall Global Climate Models: What They Do And Do Not Show ................................................14 Mitigation and Adaptation Measures a Prudent Response.................................................24 How Climate Change Could Affect Colorado’s Water Resources.......................................26 Climate Change Adaptation Recommendations & Legislation............................................27 Global Climate Models Roger Pielke, Sr. Many Contributing Influences...............................................................................................28 Water Supply Doug Kenney Divining the Future, Dividing the River.................................................................................30 Water Supply Lori Ozzello Water Managers on the Line.................................................................................................32 Agriculture Reagan Waskom Potential Ag Impacts from Climate Change . .......................................................................34 Forestry, Ecosystems and Wildlife Linda Joyce The Differences Are in the Details........................................................................................36 Air & Health Gregg Thomas, Carrie Atiyeh Health Issues Part of Climate Change Discussion......................................................................... 39 Energy Tom Plant Colorado Committed to Energy Conversion .......................................................................41 Recreation Lori Ozzello It All Begins with Snow..........................................................................................................43

Blue Mesa Reservoir

Citizen’s Guide to Colorado Climate Change

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The Most Important Natural Resource

By Nolan Doesken Colorado State Climatologist and Senior Research Associate, Colorado State University Dept. of Atmospheric Sciences

Nolan Doesken pauses near the 120-year-old weather station on the university’s Fort Collins campus.

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Essentials Climate is never stable or stationary. It varies. The world’s winds and ocean currents are in constant motion, maintaining balance. Climate is the result of laws of physics applied to an amazing combination of land, sea and air.

Climate begins with the sun, which provides the energy to drive the global climate system. Sunlight passing through the atmosphere warms the earth and then heats the adjacent air, making our planet livable. The air warms most quickly over dry ground. Over water or moist vegetation, more of the solar energy is used to evaporate and transpire water.

The rotation of the earth on its tilted axis and its continuous journey around the sun means that solar energy is distributed across the entire globe. Tropical regions get more sunlight. Polar regions get less. As the sun’s angle changes with the seasons, the distribution of solar energy constantly changes. In the mid latitudes, high latitudes and polar regions, these seasonal changes in sunlight are very large. In Colorado, energy from the sun reaching the ground is three times greater in summer than in winter.

Differences in sunlight produce temperature variations. As temperature gradients develop, winds begin to blow. The earth’s rotation causes the winds to circulate in waves and large swirls that vary in strength and location according to the season. The winds strive constantly to maintain balance, moving energy away from the tropics and towards the poles while carrying water vapor from oceans to continents and from moist to dry regions. Periodic storms may deliver much-needed water in the form of rain or snow. The changing seasons add a rhythm to the winds, to the temperature, to the rain and snow and to our lives.

Colorado Foundation for Water Education

Citizen’s Guide to Colorado Climate Change

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The seasonal cycle of temperature follows the path of the sun, but lags by a few weeks.

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weather. The largest variations occur in broad valleys in or near the mountains.

The seasonal cycle of temperature follows the path of the sun, but lags by a few weeks. The longest days of the year, when the most solar energy is striking Colorado, occur in June.

The warmest temperatures usually occur a few weeks later and continue to mid August. As days shorten and the sun drops lower in the sky during autumn, temperatures cool steadily. The coldest weather of the year occurs from late December to mid February. From the hottest days in summer, to the coldest nights of winter, many areas see swings of 100 degrees or more.

Another key feature of Colorado’s climate is the large and obvious change of temperature with elevation. Under most circumstances, temperatures are cooler at higher elevations. This is apparent year ’round but especially on hot summer afternoons.

Temperatures are typically in the 80s and 90s across the plains and lower valleys of Colorado while in the higher mountains, 60s and 70s are more typical. On the high peaks temperatures may only be in the 50s.

Temperature patterns become more complex at night and during winter thanks to mountain-valley wind patterns. At any given elevation, cold air is denser than warmer air and moves by gravity. The coldest air often settles and collects in broad valleys at night. This effect is especially noticeable when the ground is covered with snow. For example, in places like Fraser, Steamboat

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Clear-day Solar (MJ/m2-day)

Colorado’s Place in the Picture Colorado’s geographic setting explains a lot about our climate. The state is approximately half way between the equator and the North Pole—with latitudes ranging from 37 degrees north at the New Mexico border to 41 degrees north at the Wyoming border.

We are in the interior of the North American continent, far from any oceans or large bodies of water. We straddle the crest of the Continental Divide where the Rocky Mountains reach their highest elevations. The state’s elevation averages 6,800 feet above sea level, much higher than any other state in the U.S. Even our lowest areas where the many rivers that form in Colorado exit our state, are all above 3,000 feet—higher than the majority of most other states.

More than 1,000 mountain peaks in Colorado rise above 10,000 feet with 54 towering above 14,000 feet.

Latitude, elevation, location and topography all work together to produce the complex, variable and sometimes extreme climate of Colorado.

With the help of data from weather stations all across Colorado that were first installed in the late 1800s, we can describe in detail our state’s precipitation and temperature patterns.

Colorado lies far inland from any moderating influence of oceans and other large water bodies. As a result, many days are sunny with low humidity. “Three hundred days of sunshine” exclaimed 19th century promoters.

No data confirm this then, but publicists for the railroads were working hard to lure people to the West and overcome the fearful “great American desert” image that earlier explorers had described.

Colorado’s highlands have a relatively thin atmosphere, with large daily and seasonal swings in temperature, made possible by clouds or humid air.

Over much of the state, temperatures often climb by 30 degrees Fahrenheit or more during the morning and afternoon, only to cool quickly at night. Diurnal temperature variations of 40 to 60 degrees are possible during clear, dry

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Springs, Gunnison and Alamosa, frigid air may fill the valleys while surrounding mountain slopes are considerably warmer. In the winter of 1992, for example, Alamosa and the San Luis Valley were shrouded in ice fog for months while nearby Wolf Creek Pass enjoyed a sunny, mild winter.

Daily and annual temperature varies widely in Colorado, but day-to-day changes are much more dramatic and erratic east of the mountains. Cold fronts sweeping down from Canada, easily traverse the open High Plains but are blocked and modified when they cross the mountains. From fall through spring, abrupt temperature changes are common over the plains and at the eastern base of the Rockies; more gradual temperature changes occur over western Colorado.

The Front Range is also prone to downslope winds. Under certain conditions, the prevailing westerly winds passing over Colorado descend rapidly along the Front Range. As air descends, it compresses and warms— quickly replacing the existing cooler air. These winds, sometimes called chinook winds, can warm the air from a few degrees to as many as 50 in a matter of minutes.

The winds’ speed can be annoying, sometimes reaching 70 mph or more in a few preferred areas. But they bring winter warmth. The Front Range urban corridor is considerably warmer in winter than areas further east because of the effects of downslope winds. This aspect of the climate was well known for centuries.

Colorado Foundation for Water Education

Falling Water Native Americans are believed to have migrated from summer ranges on the High Plains and settled in warmer and more protected settings in the lower foothills during midwinter.

The seasons also control the movement of clouds and moisture. The storms that sweep across the mountains and plains—sometimes gently, and sometimes frightfully—deliver water to Colorado from distant oceans.

During the winter months, large gradients in temperature between the tropics and the North Pole produce a strong mid latitude jet stream—a river of constantly moving air that circles the earth swiftly from west to east. At times, wind speeds may exceed 100 mph over Colorado’s highest peaks.

These winds aloft govern the wintertime storm track over the United States and bring air masses from across the Pacific into the western U.S. The winds shift direction, from southwest to northwest and back again, as waves in the atmosphere cross the region. Air that rises up and over the mountain barrier rises and cools. If sufficient moisture is present, clouds form and precipitation may fall.

Each wave in the jet stream offers the potential for Pacific moisture and upward movement of air, essential ingredients for precipitation. The mountains of California, Oregon, Washington, Idaho, Nevada, Arizona and Utah get the first pickings for Pacific moisture. But Colorado’s high elevation require air to rise, squeezing out more of the available moisture.

The prevailing westerly winds during winter mean Colorado’s eastern plains and Front Range urban corridor are often shielded from Pacific storms.

Winter sunshine is common east of the mountains and helps make the cold temperatures seem comfortable. December through February are typically the driest months of the year east of the mountains at the very time that Colorado’s highest mountains are having their wettest weather. On average, only about 1 inch of precipitation (the melted water content of snow) falls during midwinter east of the mountains.

Fifty to 80 percent of the average annual precipitation in Colorado’s mountains falls as snow. This decreases to less than 25 percent on the Western Slope near Grand Junction and to less than 20 percent on the eastern plains near the Kansas border.

Historically, most mid winter precipitation is snow, even at lower elevations.

Snowfall totals above 9,000 feet typically range between 200 and 400 inches per year, depending on location.

Valleys receive considerably less.

Aspen, for example, annually averages about 175 inches of fresh snow; nearby mountains get more than 300.

Winter snowfall exceeds 400 inches in some of Colorado’s snowiest ranges, such as the Park Range, east of Steamboat Springs; the Elk Range in central Colorado; and the San Juans in the southwest. There are significant differences, though, in how often and how much snow falls. Occasional storms with warmer Pacific air bring rain to the lower elevations of southwest and west central Colorado.

Colorado’s northern mountains receive frequent small to moderate snows from late October into May. Much of it is fluffy, low density snow—skiers’ favorite. Colorado’s southern mountains have fewer but larger storms that often bring higher density snows.

Snow typically begins to accumulate in the mountains in October and continues until spring. This bright white coating visually assures Coloradans there will be water for the coming growing season.

Mountain temperatures stay below freezing throughout the mid winter months, allowing each new storm to deposit a new layer. This developing snow pack is the frozen reservoir that provides water for the spring and summer.

The depth and extent of snowpack varies with location, elevation and year. Melting snow provides upwards of 80 percent of Colorado’s surface water supplies. Spring and summer rains bring beneficial moisture for Colorado’s forests and grasslands, but contribute relatively little to the state’s rivers and streams.

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COLORADO PRISM 1971 - 2000 Mean Annual Precipitation 109°W

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Map prepared with the PRISM climate modeling system by the Spatial Climate Analysis Service. Oregon State University. http://www.ocs.orst.edu/prism Copyright (c)2004, OSU SCAS

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Map Created: April 2004

Transitions Large and dramatic weather changes often accompany the transition to spring.

The winds begin to slow and become more erratic. Storm systems with counter-clockwise surface winds form and sometimes stall over the Rockies, allowing moist air from the Gulf of Mexico to move northward to Colorado.

For a few hours or a few days easterly upslope flow brings moisture to eastern Colorado. These storms can be sudden and intense. Colorado still holds the U.S. record for most snow in 24 hours, from an April 1921 storm that dropped 76 inches of snow in 24 hours in the mountains immediately west of Boulder.

In March 2003, 3-7 feet of snow fell in 60 hours over the Front Range and urban corridor. These storms pose dangers for travelers and ranchers, but the role in Front Range water supply and eastern plains agriculture is large. In 2003, that one storm produced as much as 33 percent of the entire annual precipitation along the Front Range.

In the spring, snowpack begins to melt and retreat—first at lower elevations and on south facing slopes, then moving upward in elevation. Depend8

ing on temperatures and elevation, the peak streamflows from snow melt have historically occurred in May and June. Snow accumulation east of the mountains is episodic and snow cover is intermittent.

As spring progresses, the sun climbs steadily higher. As it does, the strong temperature gradients that powered the winter jet stream relax. Temperatures climb and winds weaken. Convective processes—buoyant bubbles of rising warm air—become a significant part of cloud formation and precipitation. Severe thunderstorms with hail and tornadoes are most common in spring and early summer.

May and early June can be wet and stormy over northeastern Colorado.

Eastern Colorado’s agriculture industries count on this moisture, but it is not always reliable. At the same time sunny, dry weather becomes dominant over southwestern Colorado.

June is reliably the driest month of the year for most of Colorado’s high country. This conveniently coincides with the end of the annual snowmelt cycle, and helps reduce the potential for large floods associated with rain and melting snow.

Another significant change in

winds and air masses takes place in mid summer. Tropical and subtropical moisture from the warm Gulf of Mexico and tropical Pacific drift northward over Mexico. This is a North American equivalent, albeit much weaker, to the Asian monsoon circulation.

For a few weeks in mid and late summer, this wind pattern brings moisture northward into Colorado and fuels periods of daily thunderstorm development. The mountains and valleys of southern and southwestern Colorado experience this most regularly, but the entire state is influenced. Based on long-term measurements of precipitation across the state, July and August are the wettest months of the year at places like Durango, Alamosa, Salida, and Colorado Springs.

Farther north, summer rains associated with the North American monsoon are less reliable. Locations such as Meeker, Craig and Steamboat Springs typically experience only light and infrequent afternoon thundershowers. East of the mountains along the Front Range occasionally a summer cold front from Canada coincides with a northward push of moist tropical air. The result has been extreme but localized summer rains. The Big

Colorado Foundation for Water Education

Colorado’s latitude, elevation and topography, plus its location far inland, work together to produce low humidity and more than 300 days of sunshine each year.

Water Year Average Precipitation for Selected Stations in the I-70 Transect 5.0 4.5

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Colorado Statewide Precipitation History: 1895 - 2007 23 22 21 20 19 18

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Thompson Flood on July 31, 1976, and the Fort Collins flood of July 28, 1997, are examples of this summertime situation.

As summer ends, the atmosphere becomes more stable. Dry air masses from the interior West often replace the more humid summer air from the east and south. Fewer and weaker thunderstorms form. Prolonged episodes of clear, dry weather with deep, blue skies become common, especially near the end of September and in early October. It is not always dry in autumn, however. In fact, near the Utah border, this is often the wettest time of year. Remnants of Pacific hurricanes sometimes move northward and combine with autumn midlatitude storm systems to produce significant rains. The largest floods in the history of southwestern Colorado have nearly all occurred during this time of year.

The complex variety of seasonal precipitation patterns experienced across the state makes Colorado unique. Unlike California with its single wet season (winter) and its consistent dry season (summer), Colorado can tap moisture from several sources at different times of year. If winter snows are light, spring storms can make up some of the difference. When spring storms fail, the summer thunderstorms can still help out. If summer storms are few, there is still the chance that hurricane remnants may help.

Precipitation, on average, increases with elevation as the map of Colorado average precipitation clearly shows.

Elevation gradients are most evident in winter when the strong winds lift air masses up and over the Rockies, squeezing out moisture as they go.

At other times of year, the effects of elevation are quite different. During summer, the high elevations help trigger thunderstorms.

One thing is very obvious about Colorado. Because of its inland location, moisture doesn’t always get here.

Low-pressure troughs may cross the Rockies, but they don’t guarantee precipitation. Over a year, a few major storms that deliver the bulk of the rain and snow, especially over eastern and southern Colorado. If those storms materialize, adequate precipitation falls and life is good. If not, drought and its many impacts appear.

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Citizen’s Guide to Colorado Climate Change

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least variability occurs with summer minimum temperatures. If a warming trend is occurring, it will be easiest to detect where natural variability is lowest—summer nighttime temperatures.

Historic data provide a background for understanding common frequencies and magnitude of variations. Colorado shows cool temperatures over much of the state in the 1910s and 20s, especially over eastern Colorado. This was followed by distinctly warmer temperatures throughout the 1930s. Even then there was talk of global warming.

Not only was Colorado warm, but so was much of North American and portions of Europe and Asia. As quickly as it started, temperatures dropped again in the 1940s. Except for a few warm years during the 1950s, the cooler pattern continued into the 1970s. Since that time, cold episodes have been fewer and shorter. Beginning in the late 1990s an upward trend has been evident in weather station data in most parts of the state.

Precipitation behaves much differently than temperature and is more variable. Temperature is a continuous variable while precipitation comes in episodes that only occur 2-5 percent of the time in Colorado. Even in the wettest parts of the state, most of the time it is not raining or snowing.

The year-to-year variability in precipitation in Colorado is huge. When summed over 12 consecutive months,

Colorado Statewide Mean Annual Temperature: 1895 - 2007 50

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it is the battle between subtropical, Pacific, and polar continental air that determines which years are warmer or colder than average. Also, springs and summers with generous rainfall tend to be cool while periods of drought are usually hot. The phase of the El Nino Southern Oscillation correlates with these anomalies but does not dominate the correlation.

Winter temperatures are more variable than summer temperature, and daytime temperatures are more variable than nighttime readings. The

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Rocky Ford Temperature Means and Extremes

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Temperature (°F)

Climate Variability No one lives in Colorado without realizing no two years are the same. The annual cycle, driven by energy from the sun, is a dominant control. January or an adjacent month is almost always the coldest month of the year and July, or sometimes August, is the warmest. But other than that, all bets are off. Temperatures vary widely from day to day and week to week, especially from mid autumn to late spring. But by the time you average daily temperatures over a complete annual cycle, much of these variations begin to smooth out. In most years, the mean annual temperature—average of all daily high and low temperatures—will end up within about 2 degrees of the long-term average. An extreme year may deviate from the average by 3 degrees.

Different climate drivers influence the variability in temperatures. Western Colorado and the interior mountain valley temperatures are affected by the presence or absence of winter snow cover. In a year with deep and early snows, winter temperatures can easily dip to 6-10 degrees below average for several consecutive months. The opposite occurs during open winters with limited snow cover. For the high mountains, the presence and persistence of upper level ridges (high pressure) and troughs (low pressure) dominate temperature anomalies. East of the mountains

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Colorado Foundation for Water Education

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the range in annual precipitation at individual weather stations ranges from roughly half the average in a dry year to double the average in a wet year. That is a 400 percent swing.

The 120-year series of precipitation data from Rocky Ford in the Arkansas Valley shows this clearly. Annual precipitation peaked in 1999. Three years later, it dipped to a record low.

This is the challenge of managing water resources and administering water rights in Colorado. It is the challenge of survival.

Cycles Two-year cycles, 7-year cycles, 11-year cycles and even 20-22 year cycles (called the double sunspot cycle) are apparent. At first glance the cycles look systematic and predictable. But using the records of the past to extrapolate to the future it is not clear cut.

Across Colorado, correlations with ENSO (El Nino Southern Oscillation) exist that vary regionally. El Nino conditions may correlate to wetter weather in parts of the state and drier in others. But ENSO only explains a fraction of the variability. There were periods

of time when precipitation patterns in Colorado showed a strong correlation with the sunspot cycle. At other times, those relationships did not hold.

The nature and magnitude of precipitation also varies geographically, making trend detection and interpretation difficult. Historic data show greater variability in seasonal and annual precipitation over southern Colorado compared to northern parts of the state. East-west differences are less apparent. Despite dramatic ups and downs in precipitation, there are no clear signs of either an upward or downward trend in precipitation.

All wet periods since record keeping started in the 1880s have been preceded or followed by drought.

Colorado is fortunate to have multiple and nearly independent precipitation mechanisms. 2002, an extreme drought year, proved it was possible for them all to produce limited precipitation in the same year. Historically this is rare.

Conclusion Experience shows Colorado’s climate is variable and dishes out ex-

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tremes— heat, cold, high winds, blizzards, drought and floods. Colorado’s mountains and its high elevation interest residents, visitors and climate scientists. Everybody loves following the weather, but many confuse the weather for the climate.

Climate can only be viewed as a big picture over the long haul. We know what happened through empirical data from monitoring done in the past century. That data is correlated with tree ring and ice core information that demonstrate cycles of flood and drought.

Now climate change scientists use computer models to project future scenarios. Although the models are the best tools available, they are not refined enough yet to take Colorado’s topography into account. With them, we can peer into the future and take the needed next steps: continue monitoring; compare model results to identify areas of agreement and disagreement; refine the models and the modeling assumptions; develop Colorado-focused models; and press forward with the scientific and public policy dialogue. q

Citizen’s Guide to Colorado Climate Change

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Drought

Drought

Floods

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Drought

Precipitation

1130-1180—Prolonged drought in the San Juan Basin; ancestral Puebloans in Mesa Verde abandon mesa top homes for cliff dwellings by 1200, then in a subsequent drought, abandon Mesa Verde between 1280 and 1300.

1900-1904—In southwest Colorado, the Animas River nearly goes dry.

1911—Heavy rains on Oct. 5 near Durango caused the Animas River to rise to 8 feet above flood stage.

The mid latitude, low pressure center and associated cold and warm fronts produced rainfall and floods in southwest Colorado’s Animas Valley, Durango and Pagosa Springs.

1921—June cloudbursts between Cañon City and Pueblo caused flooding which kills at least 78 people.

More than $20 million in damage reported.

1930s—A decade-long drought, worst in 1934 and then again in 1939, delivers the infamous Dust Bowl. The disaster thins the homesteader population to a more sustainable level.

1941-1949— Widespread wet weather, especially 1941-42, 1947 and 1949.

Wet period interrupted with dry mountain winters—1944-45 and 1945-46 with very low snowpack accumulation.

1500s—Tree ring reconstruction shows a megadrought, stretched over a large part of North America; lasts decades.

Floods

1864—Heavy rain on May 19-20 over the upper basin of Cherry Creek caused flooding that kills 19 people along Cherry Creek and the South Platte River in Denver.

1896—A July 24 cloudburst centered on Cub Creek near Morrison kills 27 people.

Floods

1904—Heavy rain on Aug. 7 causes a train wreck near Pueblo. One hundred people died.

Precipitation

1905-1929—Longest recorded wet period in Colorado history.

Significant but brief droughts did occur during this period, most notably 1910-11, and 1924-25.

Snow

1913—The worst Front Range snowstorm in recorded history (Dec. 1-5) strands hundreds of train passengers on dozens of trains. The storm sprawls from Cheyenne, Wyo., south to Raton, N.M.

Tornadoes

1901—Small tornado in June injures dozens at Overland Park Race Track.

1927—Snowmelt and heavy rains in June flood the Rio Grande River from Rio Grande Reservoir to past Alamosa. Five bridges were destroyed and train serviced halted.

Three persons die.

Snow

1921—An April 14-15 storm drops 76 inches of snow—the most in 24 hours in U.S. history—at Silver Lake in the Boulder watershed.

Snow

1848—On his fourth expedition, John C. Fremont and his party are trapped by snow in southwestern Colorado’s La Garita mountains while looking for a railroad route through the Rockies; 10 men die.

1888—January 11-13 Eastern Colorado is hit by windblown snow and frigid cold during Great Plains blizzard.

Denver snowstorm, 1913

Trinidad flood, 1904

1899—Near Crested Butte, a mining camp weather station measures record 249 inches (20 feet, 9 inches) of snow for the month of March.

Tornadoes

1915—A July tornado, accompanied by hail, storms through homesteads along Little Cat and Mud creeks, southwest of Lamar.

Two children die and 22 people are injured.

1922—A November tornado hits a Lincoln County farmhouse, 20 miles north of Sugar City. Four people die.

1916—Eighteen people are injured when a tornado razes buildings in Yuma

Tornadoes

1869—A tornado in November destroys lower Georgetown.

Tornadoes

Mesa Verde, 1891

1924—Nine children and a woman die in August when a tornado hits a farmhouse near Thurman in Washington County.

1928—A June tornado near the ColoradoOklahoma border devastates seven farms and kills two people in Baca County.

Dust storm, circa 1934 Floods

Snow

1933—Three to nine inches of rain in 9 hours on August 2-3 caused Castlewood Dam on Cherry Creek to fail.

Seven people die in Denver. Damage was estimated at $1 million.

1946—An estimated 50 inches fell during an early blizzard, isolating eastern Colorado until warm weather melted the snow.

1935—Up to 10 inches of rain fell in the Republican River Basin in Eastern Colorado on May 30-31, causing six deaths and more than a million dollars in damage.

Snow

1930—A brief but wicked November blizzard precludes a decade of drought.

1931—In Kiowa County, five children and a bus driver freeze to death when their school bus gets stuck during a March blizzard. It takes rescuers 36 hours to reach them.

Sources: NOAA, Colorado Climate Center, State of Colorado, USGS, Ancestry.com, Denver Museum of Nature and Science

12

1949—A combination of cold temperatures, heavy snow and days of howling winds bury houses and barns from Fort Collins and Greeley northeast across Nebraska.

Colorado Foundation Foundation for for Water Water Education Education Colorado

Snowstorm, Douglas County, 1946

Drought

Floods

Drought

Floods

Precipitation

Drought

1952-1956—Another statewide drought visits. It’s worst for Front Range cities and, accompanied by extreme heat, especially intense in 1954 and 1956. It ends abruptly in 1957 with one of Colorado’s wettest years in history.

1965—Localized, torrential rainfall in June bombards the South Platte River Basin, causing the granddaddy of floods, notably in Plum Creek and the South Platte through Denver, and Bijou Creek to Fort Morgan. The Arkansas and South Platte river basins are declared major disaster area. Two people die when a Prowers County dam fails, damaging Holly, Granada and Lamar. Overall damage estimated at $600 million; 24 people die.

1976-1977—Extreme lack of snow causes a drought in Colorado and most of the western U.S. The driest winter on record sends a shock through the recreation industry and sets the stage for rapid development of snowmaking at major resorts and the water rights to support that.

1981—Intense rains of up to 10 inches near Trinidad on July 2-3 caused the failure of a railway bridge and derailment of a train.

1990-1999—the wettest decade in recorded history over much of southeastern Colorado.

Floods

Drought

1973—Prolonged rains of up to 6 inches on May 5-6 in the South Platte Basin, along with melting of a large snowpack, produces major flooding for two weeks along the South Platte River. Damages estimated at around $120 million.

1981— Drought prompts Colorado to develop its first statewide drought plan.

2002—-An intense drought lingers for a water year and the entire state experiences a rapid drawdown of reservoirs and the lowest streamflows on record for many rivers.

The drought affects portions of 30 states and does more than $10 billion in damages.

The water shortages are the impetus for many new laws, water conservation education and a spectrum of water storage plans, projects, exchanges and leases.

Floods

1951—More than 4 inches of rain fell Aug. 3-4 at Waterdale and caused a dam failure on Buckhorn Creek. Four people die and many were homeless.

1957—Four inches of rain in 5 hours in the Toll Gate Creek Basin causes flooding in Aurora.

Cold Snaps

1962—Extreme damage to Colorado fruit industry.

Flood damage, Denver, 1965

1976—July 31 cloudbursts produce up to 12 inches of rain near Glen Haven, mostly between 6 and 11 p.m., causing a record flood on the Big Thompson River. Approximately 150 people died.

1982—On July 15 Lawn Lake Dam in Rocky Mountain National Park fails, killing two people and causing around $30 million in damage near Estes Park.

1982—Christmas Eve blizzard pulverizes the Front Range and other parts of Colorado, stranding holiday travelers.

1983—Record snowstorms kick off winter in mountains.

1985—Four feet of deep and drifting snow sock Colorado’s eastern plains on October 24-26.

1981—A June tornado in the heart of Thornton damages nearly 800 homes and injures 42.

1951—Heavy, wet snow and high winds on Dec. 29-31 blitz western Colorado. Mountain passes close for days.

1988—June storm spawns five tornadoes in metro Denver and causes $15 million in damages.

1957—Southeastern Colorado blizzard on April 1-2 drops more than 17 inches of snow.

Precipitation

1957— The wettest year in recorded Colorado history (statewide average).

Cold Snaps

Rain, Lake County, 1942

Snow

1977—After months of drought, a March blizzard with 70 mph winds assaults east central and northeastern Colorado. Snowdrifts combine with layers of blown topsoil.

1999—A Dec. 3rd storm leaves Lots of snow and some records fall, Cuchara receives a record-breaking 61.25 inches of snow, 32.4 inches at Rye, 10 inches of snow in the Black Forest and Woodland Park, 16 inches at Beulah as winds gust to 45 mph and higher in some areas.

Snow

Tornadoes Snow

Snow

1983—Week of subzero temps in December.

Tornado, Weld County, 2001 Tornadoes

1990—A June tornado destroys 80 percent of Limon’s business district, along with 228 of the town’s 750 homes.

Hail

1990—Softball-sized hail destroyed roofs and cars in July, causing $625 million in total damage.

1993—222 severe hailstorms reported for the year.

Hailstones, 1978

1985—Maybell records a low of -61F on Feb. 1.

1989—”Alaska Blaster” posts frigid temps and snow blankets the state in February.

Citizen’s Guide Guide to to Colorado Colorado Climate Climate Change Change Citizen’s

Snow

2003—A monster March storm on the Front Range drops 7 feet of snow in some foothills locations.

2005—An April 10 snowstorm strands travelers, knocks out power, closes highways and dumps up to 30 inches of snow in some places.

2006-2007—A series of December-January blizzards wallops Colorado, downing power lines, stranding cattle and closing schools.

Tornadoes

2007—The first killer tornado in 47 years strikes Holly.

2008—An F3 (136-165 mph winds) May tornado sweeps north, from Platteville to Windsor, leaving a swath of wreckage in its wake.

13

Brad Udall of the research faculty at the University of Colorado and director of the Western Water Assessment, a joint venture of the university and the National Oceanographic and Atmospheric Administration, poses with global weather patterns projected onto a sphere at the NOAA’s Science on a Sphere theater in Boulder.

14

Colorado Foundation for Water Education

Global Climate Models:

What They Do And Do Not Show

By Brad Udall Director CU-NOAA Western Water Assessment

Computer-based climate models allow scientists to investigate how changes in sunlight, concentrations of greenhouse gases, tiny atmospheric particles called aerosols, and even volcanoes, might affect the Earth’s climate.

The models are critical because scientists have no way to otherwise experiment on the Earth. Today’s sophisticated global climate models, or GCMs, are derived from the first ones created in the 1960s and from weather prediction models dating to the 1950s. Projecting climate is easier than predicting weather because scientists are not interested in the forecasts for a given day in the future. Instead, they are concerned about long-term averages, extremes and patterns that determine climate.

At their heart, GCMs are mathematical representations of the Earth’s natural systems including the atmosphere, oceans, icecovered areas, land and vegetation. The models are some of the most complex computer codes written by humans and run on the largest supercomputers in the world. Approximately 25 climate models have been developed in about 12 modeling centers around the world. The U.S. has three major modeling centers: NOAA’s Geophysical Fluid Dynamics Laboratory in Princeton, N.J.; NASA’s Goddard Institute for Space Studies in New York City; and Boulder’s National Center for Atmospheric Research.

Citizen’s Guide to Colorado Climate Change

15

Computer models depict the Earth Climate model projections are deas a series of 3D gridboxes (Figure A) pendent on the amount and timing approximately 120 miles on a side with of future greenhouse gas emissions, multiple layers for the atmosphere and and these are provided as an indepenoceans. The models can produce so- dently derived input. Because no one lutions for past climates over the last can know how technology will evolve, several hundred years, as well as for population will grow, or how the Earth’s several hundred years into the future. economies will fare in the 21st century, Air temperaeconomists cretures, precipita- Model Gridboxes ated numerous tion, winds, sea standardized fusurface temperature greenhouse Horizontal Grid tures, snowpack gas emissions (Latitude-Longitude) and many other scenarios known types of data are by their IPCC acVertical Grid (Height or Pressure) calculated in each ronym SRES, gridbox for about for Special RePhysical Processes in a Model every 20-minute port on Emission modeled period Scenarios. They and are stored range from very in large datasets “green“ futures later analyzed with a rapid tranfor trends. Many sition to nonfosSource: NOAA aspects of the sil fuel energy Earth’s climate, and slow populaFigure A: An example showing how climate models represent the Earth as a series of gridboxes. Many including large tion growth, to variables such as temperature, wind and precipitation storm systems, fossil fuel intenare calculated for each gridbox during each modeled trade winds, jet sive futures with timestep. Source: NOAA streams and large population year-to-year variability like El Nino, are growth. Humans currently emit about accurately simulated. Climate model 8 billion tons, or 8 gigatons, of carbon projections are typically shown for the annually. The standard scenarios range year 2100 but results for intermediate in future emissions from 5 to 30 billion years are also available. tons of carbon by 2100. The scenarios The current generation of com- are used by all the major modeling puter models—when initialized with groups so that climate model outputs known conditions on the Earth and can be easily compared.

Different climate models show driven by everything known to affect climate —faithfully reproduces the cli- different temperature responses to mate of the past 100 years when the the same greenhouse gases. This warming effects of greenhouse gases is called ‘climate sensitivity’ and it are considered (Figure B). Along with varies between models because the observations and known atmospheric Earth contains many self-reinforcing physics, this is one of the main rea- cycles1 which amplify temperature sons the Intergovernmental Panel on increases, are poorly understood Climate Change, or IPCC, 4th Assess- and are handled in different ways ment report concluded “most of the by different models. One important observed increase in globally aver- self-reinforcing cycle is the relationaged temperatures since the mid- ship between snow cover and tem20th century is very likely due to the perature—when snow covered areas observed increase in anthropogenic melt due to warming, the newly exposed and much darker land surface greenhouse gas concentrations.”

Besides complex GCMs, many can then absorb more heat which other, simpler computer climate leads to yet more warming. This is a models are available. All point to key reason why the arctic is warming warming as greenhouse gases are much more than other parts of the planet. Similarly, the atmosphere can added to the atmosphere.

Solar Terrestrial Radiation Radiation

ATMOSPHERE

Advection

Snow

Momentum Heat Water

CONTINENT

Sea Ice

Mixed Layer Ocean

Advection

OCEAN

hold substantially more water vapor (a greenhouse gas much more powerful than CO2) as it warms, resulting in yet more warming. The water normally in the top layers of the soil can keep the land surface cool but with warming evaporation increases and soil moisture can be reduced which causes more warming.

Current climate models suggest that for a doubling of CO2 climate sensitivity likely ranges from 4 to 8 degrees Fahrenheit with a mean of 6 F, but higher outcomes are possible.2 By comparison, the last ice age was approximately 9 F colder than present. Without any self-reinforcing cycles, a doubling of CO2 would lead to a temperature increase of approximately 2 F. Hence, the self-reinforcing cycles are believed to be quite large and are critical to understanding climate change.

Recent research suggests the next generation of models will not be able to significantly reduce the uncertainties around future temperatures, even with known greenhouse gas emissions. The reason: the possibility that arctic warming might result in the release of billions of tons of CO2 and methane currently stored in arctic soils, leading to considerable additional warming.

Most scientists believe that at global and continental scales the models project future temperatures with reasonable accuracy, but only roughly project precipitation.

At regional scales the model results are coarse largely because of the gridboxes’ substantial size. Current models can only approximate the results of atmospheric processes that operate at spatial scales smaller than their gridboxes, or at time scales shorter than their timesteps.

Clouds, and rainfall within clouds, are two critical examples. In Colorado, projections of precipitation suffer because the large gridboxes blur the mountains’ sharpness, and much of our precipitation is the result of the Rockies’ steep terrain.

Gridbox and timestep sizes will decline as computer power increases, and many of these problems are ex-

Climate scientists call these ‘positive feedbacks’. The term ‘positive’ is used not because they are good, but because the feedbacks are additive to warming caused by the initial rise in CO2.

2 Prior to the industrial age, atmospheric concentrations of CO2 were 280 parts per million by volume (ppm). Concentrations are now almost 40 percent higher, approximately 385 ppm, and rising at 2 ppm per year. Most scientists think that CO2 will at least double to 550 ppm before human actions stabilize it.

1

16

Colorado Foundation for Water Education

pected to diminish over time.

To overcome the gridbox limitations, statistical methods—and even high resolution regional climate models—are sometimes used to downscale the GCM data to a regional level.

Such methods can provide a glimpse into our possible future climate, but all climate model data, especially precipi-

tation, should be used with caution.

Scientists believe that averaging the results of all models provides a better answer than using the results from any one model. Hence, many of the results from GCMs are presented as multimodel averages. This phenomenon is also true of current weather models, partially because the models tend to

generate results that scatter randomly around the correct answer. When averaged, the random errors cancel out, leaving a multi-model result closer to the correct answer. Paradoxically, even inaccurate models can provide useful information in this situation. Most climate scientists believe that there will never be one best model.

Global Mean Surface Temperature Anomalies

a) 1.0

Anthropogenic and Natural Forcings

Figure B: Modeled vs. measured historic temperatures with (top) and without (bottom) the effects of greenhouse gases. In upper figure, the yellow band represents all models and the mulit-model average is the red line. All climate forcings, such as greenhouse gases, are included in the projections. Actual temperatures are in black. In the lower figure, which uses no greenhouse gas warming, the blue band represents all models and the blue line is the mulit-model average. Actual temperatures are in black. Note that the models project 20th century temperature correctly only when greenhouse gases are considered. Source: IPCC Working Group 1, Technical Summary, 2007.

0.5

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©IPCC 2007: WG1-AR4

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Citizen’s Guide to Colorado Climate Change

17

Global Climate Trends during the 20th Century The 2007 IPCC 4th Assessment Report found climate system warming is unequivocal with observed increases in air temperatures, widespread melting of snow and ice, and rising global average sea level. Eleven of the last dozen years rank among the 12 warmest years since 1850. Warming over the last 100 years has been 1.3 F over the last 50 years, 1.2 F. Temperature increases have been widespread, with high northern latitudes warming more than the average. Ocean temperatures increased notably. Decreases in snow and sea ice are evident. Average Northern Hemisphere temperatures are very likely higher than during any other 50-year period in the last 500 years and are likely higher than the highest in the past 1,300 years. In both hemispheres, mountain glaciers and snow cover declined on average. Precipitation increased significantly in eastern North America. Globally, the area affected by drought has likely increased since the 1970s. Extreme weather events have changed in intensity and frequency during the last 50 years. It is very likely that cold days, cold nights and frosts have become less frequent over land, and hot days and nights have become more frequent. It is likely that heat waves have become more frequent over most land areas. The frequency of heavy precipitation events likely increased over most areas.

Annual Mean Temperatures, 2000-2006 Departures from 1895-2000 Mean.

Composite Temperature Anomalies (°F) Jan to Dec 2000-2006 Versus 1895-2000 Longterm Average

NOAA/ESRL PSD and CIRES-CDC

-3.00

-1.00

-2.00

0.00

2.00

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3.00

Non-standardized. Units: Degrees F. Figure 1: Temperature changes 2000-2006 compared to 1895-2000 mean. Source: NOAA Climate Diagnostics Center

Upper Colorado Basin Mean Annual Temperature 48

Data from PRISM: 1895-2006.

Annual Mean Temp (°F)

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Degrees F. Annual 11-year running mean

41 1890

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Figure 2: Upper Colorado Basin Mean Annual Temperatures by year and with 11-year running mean. Note that the temperatures have increased by approximately 2 F since 1970.

Source: Kelly Redmond, Desert Research Institute

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2010

Western U.S. Climate Trends during the 20th Century Across the West, large temperature increases occurred, the highest in the Southwest (Figures 1 and 2). Outside of Alaska, these are the largest increases in the U.S. Large areas of the West have experienced reductions in April 1 snowpack over the last 50 years (Figure 3). These are most noticeable in the low-lying mountains of the West, including the Pacific Northwest and the northern mountains of California.

Much of the reductions have been attributed to increasing temperatures.

It is unclear is whether snowpack reductions occurred in Colorado during this period—different studies produced conflicting results. Colorado

Colorado Foundation for Water Education

has the highest average elevation in the nation. Winter temperatures substantially below freezing at higher elevations might protect the state’s snowpack. Still, across the West, including Colorado, the proportion of total annual precipitation falling as rain rather than snow has been increasing over the last 50 years.

No clear trend in precipitation emerges over the last 100 years. There is evidence of increasing drought severity and length in the American Southwest (Figure 4). Streamflow runoff timing has advanced by up to 20 days in large areas of the West, in many cases mirroring the same locations with reductions in snowpack (Figure 5). Advances in timing are not yet evident in Colorado.

Global Climate Projections for the 21st Century The IPCC projects global warming of about 0.7 F over the next 20 years, regardless of greenhouse gas emissions during the period. About half of the anticipated warming is ‘committed warming,’ reflecting the fact that the climate in general and the oceans in particular are slow to respond to the warming caused by existing greenhouse gasses.

Beyond 2030, temperatures will increasingly depend on actual greenhouse gas emissions. The mid-range estimate for global temperature increases at 2100 range from 3.25 F to 7.2 F relative to the 20th century average.

Warming is expected to be greatest over land and most at high northern latitudes. Snow-covered areas are expected to contract and sea ice to shrink. Heat waves and heavy precipitation events are likely to become more frequent.

Tropical cyclones probably will become more intense, but it is unknown if they will become more or less frequent.

Mid latitude storm tracks are projected to move poleward with associated changes in wind, precipitation and temperatures, continuing the broad pattern of observed trends over the past 50 years. At higher latitudes, increased precipitation is very likely. In most semi-arid subtropical land areas (Figure 6) precipitation decreases are projected. Additional climate change would continue well into the 22nd century, even if greenhouse gas concentrations were stabilized at 2100.

Linear Trends in April Snowpack (1957-1997) 80% 60% 40% 20%

Observed CT Trends (1948-2000)

60° >20d Earlier 15-20d Earlier 10-15d Earlier 5-10d Earlier <5d Earlier 5-10d Later 10-15d Later 15-20d Later >20d Later

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Figure 3: Linear Trends in April 1 snowpack for the period 1950-97. Source: Mote et al., 2005.

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Figure 5: Observed trends in streamflow runoff timing, 1948-2000, in days runoff occurs earlier. Source: Stewart et al., 2004

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Figure 4: Trends in Drought Severity 1915 to 2003. Upward trends are in red triangles, downward in blue.

Note the increasing trend in the American Southwest. Source: Andreadis and Lettenmaier, 2006.

multi-model

A1B

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©IPCC 2007: WG1-AR4

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Figure 6: Projected multi-model mean patterns of precipitation changes at 2100 under mid-range greenhouse gas emissions with December, January and February on left, and June, July and August on right. Colors are shown where at least 66 percent of the models agree and stippling where 90 percent of the models agree on the sign of the change. Note that many already dry areas such as the American Southwest and the Mediterranean are projected to dry further, and many wet areas in the tropics and high northern latitudes are expected to get wetter. Source: IPCC Working Group 1 Summary for Policy Makers, 2007.

Citizen’s Guide to Colorado Climate Change

19

North American Climate Projections for the 21st Century Warming in North America is likely to exceed the global average by 2100, with summer warming to exceed winter warming in the lower 48 states (Figure 7). Less precipitation is likely in the Southwest, while the northern states can expect more (Figure 8).

Multi-Model Range and Mean of Very Likely Annual Temperature Increases (F) in U.S. Southwest GHG Emissions

2010-2029

2040-2059

2080-2089

Low (“B1”)

1.0-3.7 (mean=2.3) 1.6 - 5.6 (mean = 3.6)

2.5-7.8 (mean = 5.2)

High (“A2”)

1.3 - 3.5 (mean = 2.4)

5.6 - 11.8 (mean=8.7)

2.6 - 6.4 (mean=4.5)

Table 1: Multi-model range and mean of projected future temperatures in the American Southwest (Nevada, California, Arizona, New Mexico, Utah and Colorado) for two different emissions scenarios at three different 20-year future periods. Source: Michael Wehner, Lawrence Livermore National Laboratory.

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Figure 7: Projected North American multi-model mean temperature increase at 2100 under mid-range emissions.

Winter is on left, summer on right. Source: IPCC Working group 1, Chapter 11, Regional Projections, 2007.

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Figure 8: Projected North American multi-model mean precipitation changes at 2100 under mid-range emissions.

Winter is on the left and summer the right. Source: IPCC Working group 1, Chapter 11, Regional Projections, 2007.

Multi-model Mean and Range of Very Likely Annual Precipitation Changes (%) in U.S. Southwest GHG Emissions

2010-2029

2040-2059

2080-2089

Low (“B1”)

-9.8 to +10.4% (mean=-1.2%)

-11.7 to +6.7% -14.6 to +11.3% (mean=-2.2%) (mean=-1.6%)

High (“A2”)

-9.9 to +8.7% (Mean= -0.6%)

-19.9 to +14.7% -27.3 to 19% (Mean= -2.5%) (mean = -4.2%)

Table 2: Multi-model range and mean of projected future annual mean changes in precipitation in the American Southwest for two different emissions scenarios at three different 20-year future periods. Source: Michael Wehner, Lawrence Livermore National Laboratory.

20

Southwestern U.S. Climate Projections for the 21st Century For at least three reasons, current climate models do not provide entirely suitable temperature and precipitation projections for Colorado. Unlike many states where one location is representative of the climate for the entire state, Colorado’s climate varies tremendously from place to place.

Secondly, current models poorly represent our complex topography.

Rather than having sharp 14,000-foot mountains, the models’ large gridboxes represent the Rockies as a broad hump. Finally, most climate models indicate that the deserts of the American Southwest will expand northward and storm tracks will move northward. Unfortunately, the increases are highly variable from model to model and how these changes might affect Colorado are uncertain.

Southwestern U.S. Temperature Projections By 2100 the amount of warming is highly dependent on emissions of greenhouse gases during the 21st century (Table 1, Figures 9 and 10). An important note: The amount of warming in the interior of North America and Colorado will be substantially more than the global average. Summer warming is expected to be greater than winter warming, partially because of increased evaporation and reduced soil moisture.

Southwestern U.S. Precipitation Projections By 2100 the change in mean annual precipitation in the American Southwest using many models and many emission scenarios shows a slight decline (Table 2, Figures 11 and 12). The range of results from individual models is large, however. For example, results in 2100 range from increases of +19 percent to decreases of -27 percent.

Colorado Foundation for Water Education

On average, the models show a slight shift towards more winter and less summer precipitation. One consistent model result is a significant decrease in precipitation in March, April and May,

which may indicate an earlier transition to spring. This agrees with the IPCC finding that snow season length and depth are very likely to decrease for most parts of North America.

SRES A2 16Mod 2080-2099 ANN Temperature

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Figure 9: Multi-model mean annual temperature increase at end of the century under high emissions. Source: Michael Wehner, Lawrence Livermore National Laboratory.

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Figure 10: Multi-model mean annual temperature increase at the end of century under low emissions. Source: Michael Wehner, Lawrence Livermore National Laboratory.

SRES B2 16Mod 2080-2099 ANN Precipitation

SRES A2 16Mod 2080-2099 ANN Precipitation

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Figure 11: Multi-model mean change in annual precipitation at end of century under high emissions. Blue indicates increasing precipitation while tans and reds indicate decreasing precipitation. Source: Michael Wehner, Lawrence Livermore National Laboratory.

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Figure 12: Multi-model mean change in annual precipitation at end of century under low emissions. Source: Michael Wehner, Lawrence Livermore National Laboratory.

Citizen’s Guide to Colorado Climate Change

21

Projected Advances (2040-2059)

60°

40°

>35d Earlier 25-35d Earlier 15-25d Earlier 5-15d Earlier <5d Earlier 5-15d Later 15-25d Later 25-35d Later >35d Later

200° 220° 240° 260° Figure 13: Projected advances in 2040-2059 in the day of year with peak streamflow relative to average timing from 1951 to 1980. Peak streamflow in Colorado advances from 5 to 25 days earlier. From Stewart et al., 2004.

Southwestern U.S. Snowpack and Runoff Projections Like most Western states, Colorado relies heavily on a large natural reservoir of winter snowpack. It stores copious winter precipitation until spring when the state’s large network of reservoirs can capture and store runoff for later use.

Climate models consistently indicate that warmer temperatures will lead to a shorter winter with earlier spring runoff (Figure 13) and reductions in late summer flow. These same models indicate that if future precipitation stays the same, runoff will decrease because of increased evaporation.

The potential impacts of climate change on the Colorado River’s runoff were first studied in 1979 and more than 20 different climate change studies have been published in the intervening 30 years. Ten were released in the last four years. All the studies projected future runoff declines, and depending on the method used, reductions in average streamflow at 2050 range from 5 percent to almost 50 percent.

One 2006 study (Christensen and

Lettenmaier) used 11 climate models and two different greenhouse gas emissions scenarios. It showed that by 2100 little change in total annual precipitation—approximately less than 1 percent. But substantial warming resulted in significant declines in April 1 snowpack. Slight shifts towards more winter precipitation apparently held declines in runoff to approximately 10 percent (Table 3).

Most of the other river basins in Colorado remain unstudied, with the exception of a paper by the USGS’s Chris Milly, on future runoff changes for the entire U.S. by river basin.

Milly used multiple GCMs to investigate future changes in flow. The Upper Colorado showed 10 to 25 percent reductions, the Rio Grande 5 to 10 percent reductions, and the Arkansas 2 to 5 percent reductions by 2050. Changes in the South Platte and North Platte showed very small changes ranging from -2 to +2 percent. The agreement across models on the direction of the change was in general quite high, especially for the Colorado River (Figure 14).

2010-2029

2040-2059

Adaptation to Climate Change Much of the recent focus on climate change has been on projected impacts and ways to reduce greenhouse gas emissions so the effects are avoided, rather than on how to adapt to the anticipated changes. However, already committed warming means adaptation will be necessary regardless of mitigation. Adaptation will occur in many forms, from installing air conditioners and evaporative coolers, to protecting water supplies, to establishing better drought plans, to improving water conservation practices, to building flood control infrastructure, to reducing the possibility of catastrophic forest fires. In many places, society is just beginning to consider how to reduce its vulnerability to climate change through adaptation.

Water adaptation will be critical. Water planning in the past has been based on the assumption that the range of 20th century streamflows and water demands will adequately bracket the range of future climate. Climate change will fundamentally alter the hydrologic cycle, invalidating the assumption. As the planet warms, changes in atmospheric physics mean the atmosphere will be able to hold substantially more moisture. This implies, paradoxically, both more evaporation and drought, and also more intense storms. Hence, many of the assumptions about the reliability of our water supplies will need to be revisited. Colorado’s Climate Action Plan explicitly considers water. It identifies the need for continued scientific investigation on impacts such as changes in snowpack; development of regional hydrologic models to project future water supplies; analysis of changes to water rights; and the impacts on interstate compacts. q

2080-2089

Emissions ->

Low

High

Low

High

Low

High

Temperatures in F

2.3

2.2

3.7

4.6

4.9

7.8

In F

Annual Precipitation Change

-1%

-1%

-1%

-2%

-1%

-2%

Relative to Historic Run

April 1 Snowpack Change (Snow Water Equivalent)

-15%

-13%

-25%

-21%

-29%

-28%

Relative to Historic Run

Runoff Change

0%

0%

-7%

-6%

-8%

-11%

Relative to Historic Run

Table 3: Future Colorado River Temperature, Precipitation, Snowpack, and Runoff Results from Christensen and Lettenmaier, 2006, for three future periods using a low (B1) and high (A2) emissions scenario.

22

Colorado Foundation for Water Education

Comments

Milly, 2005

58%

87% 71%

+5%

62% 96%

97%

62%

58%

+2%

62% 75%

67%

100%

-2% 67% -5%

67%

-10%

Decrease

67%

+10%

Increase

+25%

-25% Figure 14: Projected median reductions in streamflow by 2050 across the U.S. as determined by multiple GCMs are shown in colors. Percents refer to the numbers of models that agree on the direction of the change. Source: CCSP SAP 4.3

References Web Sites Intergovernmental Panel on Climate Change: www.ipcc.ch Environmental Protection Agency: www.epa.gov/climatechange National Oceanic and Atmospheric Administration: www.noaa.gov/ climate.html U.S. Climate Change Science Program: www.climatescience.gov National Center for Atmospheric Research: www.ncar.ucar.edu/ research/climate Western Governors: www.westgov. org/wga/initiatives/climate/index. htm Western Climate Initiative: www. westernclimateinitiative.org/

U.S. Climate Action Partnership: www.us-cap.org Colorado Climate Center: ccc.atmos. colostate.edu/

Global Climate Models: http:// en.wikipedia.org/wiki/Global_ climate_model

Greenprint Denver: http://www. greenprintdenver.org/ Documents National Academy of Sciences Understanding and Responding to Climate Change: http://dels. nas.edu/dels/rpt_briefs/climatechange-final.pdf Statement from 11 National Academies on Climate Change: http://www.nationalacademies. org/onpi/06072005.pdf IPCC Synthesis Report : www.ipcc. ch/pdf/assessment-report/ar4/syr/ ar4_syr.pdf IPCC Summary for Policy Makers— Science: www.ipcc.ch/pdf/ assessment-report/ar4/wg1/ar4wg1-spm.pdf

Pew Center on Climate Change: www.pewclimate.org

National Integrated Drought Information System: www. drought.gov

Rocky Mountain Climate Organization: www. rockymountainclimate.org

IPCC Summary for Policy Makers Adaptation: www.ipcc.ch/pdf/ assessment-report/ar4/wg2/ar4wg2-spm.pdf IPCC Summary for Policy Makers— Mitigation: www.ipcc.ch/pdf/ assessment-report/ar4/wg3/ar4wg3-spm.pdf

American Association for the Advancement of Science Climate Change Policy Statement: www. aaas.org/news/press_room/ climate_change/mtg_200702/aaas_ climate_statement.pdf American Geophysical Union Climate Change Policy Statement: www.agu.org/sci_soc/policy/positions/ climate_change2008.shtml American Meteorological Society Climate Change Policy Statement: www.ametsoc.org/ policy/2007climatechange.pdf Colorado Climate Action Plan: www.cdphe.state.co.us/ic/ ColoradoClimateActionPlan.pdf U.S. Climate Change Science Program: www.climatescience.gov (See especially the ‘Synthesis and Assessment,’ or SAP, products.

3.3 deals with climate extremes and 4.3 deals with water and natural systems.)

Books Spencer Weart—“Discovery of Global Warming” http://www.aip.org/history/climate/ index.html Richard Alley—“Two Mile Time Machine”

Citizen’s Guide to Colorado Climate Change

23

Mitigation And Adaptation Measures A Prudent Response

By Brad Udall

Adaptation, or adapting to the impacts of climate change, and reducing greenhouse gas emissions to avoid the impacts in the first place—mitigation in the climate change vernacular—are being discussed vigorously around the globe, at all levels from cities to states, regions and nations. For many years adaptation and mitigation were presented as dueling alternatives. Today, it is accepted that society will have to both adapt to the effects of climate change and mitigate, or reduce, greenhouse gas emissions. Adaptation will be required because the climate system is already committed to at least another 1 F of warming due to current greenhouse gas concentrations, and mitigation will be necessary to ultimately stabilize the climate. In fact, the two approaches are complementary: The more mitigation we do, the less adaptation, and vice-versa.

Greenhouse Gas Mitigation Scientists believe that a primary cause of the warming we are now experiencing is the carbon dioxide released when we burn fossil fuels. These fuels are critical for modern life and are the energy source for approximately 90 percent of our electricity and nearly 100 percent of our transportation.

Reducing greenhouse gasses will be a substantial challenge and no single technological breakthrough is likely to provide a one-stop solution.

All plans for mitigating greenhouse gases involve short- and long-term strategies. In general, short-term solutions involve energy efficiency measures, such as using compact fluorescent light bulbs: manufacturing more fuel-efficient cars; and constructing buildings that incorporate natural

24

light, water conservation and more efficient hearing and cooling. In addition, we need to deploy cost-effective renewable energy sources such as windpower whenever possible. In the long run, many energy experts believe large-scale research and development efforts are required to find the new renewable energy technologies to supplant existing fossil fuel based technologies.

Colorado and some of her cities already have begun to mitigate greenhouse gases. Gov. Bill Ritter established the Colorado Climate Action Plan in November of 2007 with a goal of reducing greenhouse gas emissions by 20 percent in 2020 from a 2005 baseline and an 80 percent reduction by 2050. More than 20 other states also have climate action plans to reduce greenhouse gasses. Ritter’s plan has three parts: Implement bridge strategies to slow and halt greenhouse gas emissions; provide leadership to ensure that long term solutions such as renewable energy and clean coal are fully developed; and prepare the state to adapt to unavoidable climate changes.

Much of the plan is devoted to identifying suitable bridge strategies.

These include reducing:

Colorado Foundation for Water Education

• Agricultural emissions of powerful greenhouse gases such as methane and nitrous oxide; • Transportation-related emissions by adopting standards, promoting teleworking and teleconferencing; and • Energy-related emissions by promoting efficiency initiatives, renewable energy supplies and clean coal technologies.

Colorado already has made substantial gains in using renewable energy since standards were established by Amendment 37 in 2004 and later strengthened by House Bill 1281 in 2007. The amendment and legislation require 10 percent of all electric power to be from renewable sources by 2015, and 20 percent by 2020. The plan calls for the federal government to enact a nationwide climate strategy so that regional initiatives such as the seven-state Western Climate Initiative can be subsumed into a more coherent and effective national program.

Currently, 839 mayors who represent more than 80 million people have approved the U.S. Conference of Mayors Climate Protection Agreement. Under it, cities strive to reduce greenhouse gas emissions by 7 percent from 1990 levels by 2012; urge state and federal governments to meet the same target; and urge Congress to enact bipartisan greenhouse gas legislation.

At least three major blocks of states are working to reduce greenhouse gasses. In 2005 seven northeastern states agreed on a plan to reduce power plant greenhouse emissions by 10 percent in 2019.

Six states and one Canadian province associated with the Midwestern Governors’ Association signed an accord in November 2007 to establish greenhouse gas reduction program by 2009. And in the West, the Western Climate Initiative involves a similar program with seven participating states and two Canadian provinces. Colorado is an official observer of the WCI process.

On the congressional level, leg-

islators have introduced numerous bills to reduce greenhouse gas emissions. Many observers believe a federal program is inevitable, although the exact timing is unknown. Reduction of greenhouse gasses on a large scale will involve putting a price on carbon emissions. Most approaches involve a “cap and trade” program modeled after an effective federal effort to reduce power plants’ sulfur dioxide emissions. Cap and trade programs provide permits to emit a certain amount of pollutants. Other approaches being considered involve carbon taxes.

In Colorado, Aspen, Basalt, Boulder, Carbondale, Denver, Dillon, Durango, Frisco, Glenwood Springs, Gunnison, Nederland, New Castle, Pagosa Springs, Telluride, Crested Butte and Westminster signed the Mayors Climate Protection Agreement. Many of them have established or are working on climate action plans; Denver’s plan set a target of reducing emissions by 25 percent in 2020.

Aspen and Boulder enacted municipal taxes to support local mitigation efforts. Boulder’s tax, passed by 58 percent of the voters in 2006, was the first citywide mitigation tax in the nation and costs an average of $1.33 per month for each residence and $3.80 per month per business. The tax will pay for residential and commercial energy audits to advise owners how to save energy. Aspen’s tax was established in 2000 and is levied at the time of construction if homeowners exceed a certain projected energy budget. It has generated more than $8 million, applied to improving energy efficiency and increasing renewable electricity use in the Roaring Fork Valley. q

Citizen’s Guide to Colorado Climate Change

25

HOW CLIMATE CHANGE COULD AFFECT COLORADO’S WATER RESOURCES

By Brad Udall Concurrent with the publication of the Citizen’s Guide to Climate Change, the Colorado Water Conservation Board will release “Climate Change in Colorado: A Synthesis to Support Water Resources Management and Adaptation,” prepared by the University of Colorado—NOAA Western Water Assessment. The latter is a technical look at how climate change will affect Colorado’s water resources.

In addition to an executive summary, the report contains a detailed look at the observed record of Colorado’s climate, a primer on climate models, Colorado-specific projections from climate models, and implications of climate variability and change for Colorado’s water resources. Key points from the report: • Statewide temperatures have increased about 2 degrees Fahrenheit over the last 30 years. All regions, except for the southeast corner, experienced warming. Climate models show a 1 F warming in the West over the last 30 years in response to greenhouse gas emissions.

• Climate models project Colorado will warm by 2.5 F by 2025, and 4 F by 2050. Summers warm more (+5 F) than winters (+3 F) and suggest that typical summers in 2050 will be as warm or warmer than the hottest 10 percent of summers that occurred between 1950 and 1999.

• Winter projections show fewer extreme cold months, more extreme warm months, and more strings of consecutive warm winters. Between today and 2050 the January climate of the eastern plains of Colorado is expected to shift northward by approximately 150 miles. In all seasons, the climate of the mountains will migrate upward in elevation, and the climate of the desert Southwest will move up into the valleys of the Western Slope.

• No consistent trends in annual precipitation have been detected over the last 100 years. Climate models do not agree whether annual mean precipitation will increase or decrease in Colorado by 2050, but there is a seasonal shift to slightly more winter and less summer precipitation.

• The widespread reduction in snowpack found in the lower elevation mountains of the West has not been detected in Colorado. Between 1978 and 2004, the onset of spring streamflows is approximately 14 days earlier. Projections indicate that this spring pulse will continue to advance as the climate warms.

• Recent studies paint a consistent picture of declining runoff for most of Colorado’s river basins in the 21st century. Depending on the study, Colorado River runoff in 2050 drops anywhere from 5 to 45 percent.

• During the last century, tree rings indicate the West experienced less frequent and less severe droughts than during earlier periods in last 1,000 years.

• The tree ring record, standard of the last 100 years, and model projections have widespread implications for the management of Colorado’s water resources. q

Challenges Already Faced by Water Managers, and Projected Changes Issues

Observed and/or Projected Change

Water demands for agriculture and outdoor watering

Increasing temperatures raise evapotranspiration by plants, lower soil moisture, alter growing seasons and increase water demand.

Water storage and reservoirs

Changes in snowpack, streamflow timing and hydrograph evolution may affect operations including flood control and filling.

Legal water systems

Earlier runoff may confound prior appropriation systems and interstate water compacts, affecting which rights holders receive water and operations plans for reservoirs.

Water quality

Water quality is sensitive both to increased temperature and changes in patterns of precipitation, although other factors have a large impact on water quality (CCSP SAP 4.3). For example, changes in the timing and hydrograph may affect sediment load and pollution, influencing human health.

Energy demand and operating costs

Hotter air temperatures may place higher demands on hydropower reservoirs for peaking power. Warmer lake and stream temperatures may affect water use by cooling power plants and in other industries.

Mountain and riparian habitats

Increasing temperature and soil moisture changes may shift mountain habitats toward higher elevations.

Interplay among forests, hydrology, wildfires, and pests

Changes in air, water and soil temperatures may affect the relationships between forests, surface and groundwater, wildfire and insect pests. Water-stressed trees, for example, may be more vulnerable to pests.

Riparian habitats and fisheries

Stream temperatures are expected to increase as the climate warms, which could have direct and indirect affects on aquatic ecosystems (CCSP SAP 4.3). Changes in streamflow intensity and timing may also affect riparian ecosystems.

Water- and snow-based recreation

Changes in reservoir storage affect lake and river recreation activities; changes in streamflow intensity and timing will continue to affect rafting directly and trout fishing indirectly. Changes in the character and timing of snowpack and the ratio of snowfall to rainfall will continue to influence winter recreational activities and tourism.

26

Colorado Foundation for Water Education

http://www.coloradoclimate.org/ewebeditpro/items/O14F13864.pdf Public officials should exercise leadership in addressing climate change effects on water supplies.

There should be an assessment of data and data systems for understanding climate change.

Water managers should consider climate change in all water supply decisions.

There should be cooperative development of information on climate change effects in each major river basin.

Climate change effects should be considered in the new Colorado Water Conservation Board study of Colorado River water availability.

State government should develop mechanisms for compact calls for each major river basin.

There should be an assessment of knowledge about climate change effects on Colorado’s water resources.

Municipal water providers should evaluate water conservation savings, best demand management practices, and the best uses of conserved water in their systems.

Effects of water-rights transfers on agricultural economies should be minimized.

Relationships between energy and water use should be considered.

There should be information exchanges on effects of climate change on water resources.

State government should consider ways to reduce climate change effects on waterrelated recreation and tourism.

State government should consider ways to reduce climate change effects on the environment.

Use of groundwater for irrigation should be reduced until recharges match discharges.

http://www.westgov.org/wga/publicat/water08.pdf Congress should appropriate sufficient funds to conduct a portfolio assessment of federal projects to evaluate the performance of such projects given current conditions and to determine the vulnerability of projects to changing conditions.

trends, and allow for better early warning systems that (a) focus on critical or vulnerable systems; (b) deliver real-time data; (c) improve data access, storage and retrieval; (d) allow for real-time smart analysis; and (e) provide feedback and evaluation.

Federal agencies should begin a systematic updating of their respective reservoir operating plans and drought contingency plans to assure that operating plans are adaptable to a changing climate.

The federal government, in cooperation with states, should take the lead in putting together a web site to provide more useful and scaled output from climate models for the water management community.

The National Oceanic and Atmospheric Administration should take the lead in improving forecasts on multiple geographic and temporal scales and conduct additional research in collaboration with water management agencies so that forecasts can be incorporated into reservoir operations.

Water managers should take the initiative to clearly communicate their needs for applied science to the climate research community, and must seek opportunities to guide hydroclimate research in directions that will support real-world problem solving.

The United States Geological Survey, in cooperation with states, should improve monitoring and data collection to identify and respond to changing regional and local

Planning for climate change should be undertaken at all levels, from the federal government to private and public water utilities, with participation from non-governmental organizations.

More water storage should be considered, accompanied by an extensive risk and costbenefit analysis of the potential for reducing demand and increasing water use efficiency.

States that share river basin or groundwater resources should consider jointly addressing potential future supply reductions resulting from climate change.

States should examine their existing water laws and institutions to determine if they are adequate to provide sufficient flexibility to address potential climate change impacts, with a particular focus on water initiatives and programs associated with demand management, efforts to “stretch” existing supplies, water banking, and water transfers.

States should anticipate an increased need to address the forecasted effects of climate change in administrative, regulatory, and legal agreements involving water resources.

In lieu payment of taxes in connection with agricultural water transfers to cities

Funding for a statewide future water supply and demand study

Water quality protection in connection with agricultural water transfers to cities

Funding for a statewide system of real-time stream gauging and reporting

Protection for the water rights of those who make their water available for the state’s instream flow protection program

Funding for an analysis of Colorado’s share of Colorado River-apportioned water under various climate change scenarios

Land and water conservation covenants

Requirement for local land use decision makers to account for a reliable water supply in connection with future growth

Low interest loans for approved water conservation measures and storage projects

Rotational crop fallowing plans to make agricultural water available for other uses while keeping the ownership of water rights in rural agricultural communities

Establishment of a water roundtable process in every hydrological region of the state, coordinated by a statewide committee, to plan for the state’s water future

As a result of the 2002-2003 drought, the Colorado General Assembly set into place a large number of legal tools for adapting to variable and changing water supply conditions. They include, but are not limited to: Water banks for annual transfer of stored water Leases from agriculture to municipal and environmental uses

Citizen’s Guide to Colorado Climate Change

27

By Roger Pielke, Sr. Senior Research Scientist (CIRES) and Senior Research Associate (ATOC)

Natural Landscape Change

Natural Management Practices

Long-Term Weather Variability & Change

Water Resource Vulnerability

Industrial & Vehicular Emissions

Animal & Insect Dynamics

Local Human Population

Figure 2 — Water Resource Vulnerability 28

Colorado Foundation for Water Education

Many Contributing Influences The historical climate of Colorado illustrates major floods and extended periods of drought. Extreme cold and warmth have also always been a part of Colorado weather. In terms of water resources, the state has faced extended periods of drought, as well as years of generous water supply.

On the longer time period, as illustrated in Figure 1, periods of extreme drought and wet periods have been even more pronounced than in the historical record of the last century and the late 1800s.

This figure, from a study led by researchers at the University of Arizona, uses tree rings to extend precipitation data back to well before humans directly measured rain and snow. In this data set, for Lee Ferry along the Colorado River, severe droughts lasting decades, such as one in the 12th century, are clearly evident. In the period of around 800 AD to 2004 AD, 120

Flow (% of mean)

115 110

in which the effect on the climate system from forcings is often episodic and abrupt, rather than slow and gradual. Large, long-term variations in regional climate are the norm, as illustrated in Figure 1. The human effect on the climate system through such forcings as added CO2, land use change, and the input of pollution particles from fires, vehicles and industrial activity, only add to the complexity of the climate system response.

Moreover, water resources are affected by a variety of human and natural effects beyond long-term climate variability and change, as illustrated in Figure 2. These effects also interact with each other in complex nonlinear ways.

We therefore need a new approach. A way forward with respect to more effective water resource policies is to focus on the assessment of adaptation and mitigation

resources focuses on the water required for the state’s economic, social and environmental activities. This is in contrast to the GCM-focus of multidecadal global model predictions downscaled to Colorado. A top-down approach from a global perspective, in which the skill is dependent on the forecast accuracy of these global models offers a much smaller set of future scenarios for Colorado than are actually possible.

The vulnerability focus permits a much more comprehensive framework to assess threats to Colorado’s water resources. Variability and changes in the climate are just one threat to water resources. The current climate models present only a subset of the possible risk, even from climate variability and change.

The vulnerability approach uses water resource specific models and observations to determine the thresh-

Observed

80% Confidence Interval Reconstructed

105 100 95 90 85

Lowest Observed = 87% of 1906−2004 mean

80 75

800 1000 1200 Figure 1– Ending Year of 25−yr Running Mean

for example, there was a period of 25 years with 87 percent less precipitation than in the 1906 to 2004 mean.

Excessively dry periods occurred without any significant interference of humans in the climate system. Multidecadal global model predictions of the climate in Colorado actually present a less serious threat to the state’s water supply than if one of the extended past droughts reoccurred.

An assumption that projecting climate is easier than predicting weather is not correct, in my view. No global model has been able to replicate and explain the large natural variations in climate that are evident in Figure 1. In reality, the climate is highly nonlinear,

1400

strategies that reduce the vulnerability of Colorado water resources to both natural and human caused climate variability and change, as well as all other threats. Effective adaptation strategies include developing environmentally sensitive ways to accumulate water during wetterthan-average periods and building the infrastructure to transport water across large distances. They reduce the state’s vulnerability to periods of drought, regardless of how climate changes naturally and in response to human climate forcings in the coming decades.

This framework for a vulnerability assessment of Colorado water

1600

1800

2000

David Meko, Connie Woodhouse, et. al.

olds at which negative effects occur with the state’s water supplies. Using mitigation and adaptation, we need to prevent crossing the thresholds.

A vulnerability perspective, focused on regional and local societal and environmental resources, is a more inclusive, useful and scientifically robust framework to use with policymakers. In contrast to the limited range of possible future risks by current climate models, the vulnerability framework permits the evaluation of the entire spectrum of risks to the water resources associated with all social and environmental threats, including climate variability and change. q

Citizen’s Guide to Colorado Climate Change

29

Divining the Future, Dividing the River

By Doug Kenney University of Colorado Natural Resources Law Center

Interstate Obligations As the primary headwaters state for the Arkansas, Colorado, Platte and Rio Grande rivers, the impact of climate change in Colorado has the potential to affect 18 downstream states and the Republic of Mexico. Despite a lack of regional climate change studies for basins other than the Upper Colorado and the ongoing challenge of identifying clear trends regarding precipitation in the state, the majority of recent hydrologic studies suggest future declines in runoff for most of Colorado’s river basins. By the terms of nine interstate water compacts and two United States Supreme Court equitable apportionment decrees, Colorado is limited to consuming approximately one-third of the water produced by its stream systems in an average year.

The extent to which the influence of climate change on interstate apportionments is problematic for Colorado water users depends greatly on site specific circumstances, such as the seniority of rights; the availability of reservoir storage capacity; growth pressures; and the amount of water, if any, legally available for new developments. Current levels of water use in the Arkansas, Platte, and Rio Grande basins are already at or very near the state’s full apportionment, while in the Colorado River basin, some additional water may be left for Colorado.

The Colorado River and its tributaries—including the Yampa, Gunnison, and San Juan rivers—are of particular concern to the water management community on both sides of the 30

Continental Divide, as this is the only water supply source for West Slope users, and is a significant source of water exports to the South Platte, Arkansas, and to a lesser extent, the Rio Grande basins. Front Range projects importing Colorado River water include Denver Water’s Moffat Tunnel and Roberts Tunnel systems, the Northern Colorado Water Conservancy District’s Colorado-Big Thompson Project, the Homestake Project that serves Aurora and Colorado Springs, and the Frying Pan-Arkansas Project that supplies southeastern Colorado.

These and other transmountain diversions, some in operation for more than 100 years, are crucial to present and future Front Range agricultural, municipal, commercial, recreational and environmental uses.

These flows are equally valued by growing mountain communities, many of which already find it difficult to secure legal rights to waters flowing through local streams. Finding water for West Slope recreational and environmental purposes, including for endangered fish protected by the Upper Colorado Recovery Implementation Program, is also an ongoing challenge magnified by changes in streamflow amounts, timing and character. With the water needs of potential energy development factored in, climate change on the Colorado River resonates through every region and sector of the state. It is also an issue of particular concern to the six additional basin states—Wyoming, Utah, New Mexico, Nevada, Arizona and California—and Mexico that share a

hydrologic, cultural and legal connection to the river.

Climate Change on the Colorado River Determining how much Colorado River water remains for increased use and how best to use it are questions central to—and greatly complicated by—an era of climate change. Over the past century of record keeping, flows on the Colorado River have averaged almost 15 million acre feet, or MAF, per year at Lee Ferry, the official measuring point.

Flows range from a high of 24.5 MAF in 1983 to a low of 5.6 MAF in 1934.

Interstate apportionment provided by the 1922 Colorado River Compact and the 1944 U.S.-Mexico Treaty are based on the assumption of average flows of at least 16.5 MAF each year, divided among the states of the Upper Basin and Lower Basin, 7.5 MAF each, and Mexico, 1.5 MAF. In fact, a total of 17.5 MAF is actually apportioned, with the extra 1 MAF reserved for the Lower Basin if available. The error derives, in part, to unusually wet conditions before the Colorado River Compact negotiations in the 1920s, which provided negotiators with an unrealistic expectation of future flow levels.

The Colorado River Compact calls on the Upper Basin states—Colorado, Wyoming, New Mexico and Utah—to prevent flow depletions at Lee Ferry below an aggregate of 75 MAF in 10 consecutive years. Under certain circumstances, the Upper Basin states bear the burden of one-half the deficiency of the Mexican obligation.

If the river yields an average annual flow of 15 MAF, rather than 16.5 MAF,

Colorado Foundation for Water Education

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Animas-La Plata Compact Arkansas River Compact Colorado River Compact Costilla Creek Compact (Rev. 1963) La Plata River Compact Laramie River Equitable Apportionment Decree North Platte River Equitable Apportionment Decree South Platte River Compact Republican River Compact Rio Grande Compact Upper Colorado River Compact

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NEW MEXICO then the Upper Basin share may be no more than 6 MAF once downstream obligations are satisfied. Accepting this figure, Colorado’s 51.75 percent entitlement of the Upper Basin share translates to 3.1 MAF annually, rather than 3.9 MAF. The difference between these two figures, 800,000 acre feet, is significant. It roughly equals total current municipal and industrial demand in the South Platte basin.

This problematic feature of the Colorado River Compact has the potential to get considerably worse due to climate change. Colorado already uses about 2.3 MAF a year of its entitlement, which theoretically make roughly 0.8 MAF, or 800,000 acre feet per year, legally available for new development, ignoring other constraints and considerations, or slightly more than the total projected state increase in new demands by 2030. But depending on which of several, highly debatable hydrologic and legal assumptions are used, just a 10 percent decline in average stream flow might be sufficient not only to completely erode this growth cushion, but also to threaten the reliability of existing water uses.

Not surprisingly, several efforts to better estimate Colorado River flows and available supplies are ongoing, but are unlikely to provide certain answers.

Possible declines in average Colorado River flows are not the only hydrologic challenge confronting Colorado water managers. Climate variability, i.e., drought, is a long-standing concern, especially given climate studies projecting increased droughts in the future, and the current drought

crisis that has gripped the region.

River flows have been approximately 62 percent of the 30-year average in 2000, 59 percent in 2001, 25 percent in 2002, 51 percent in 2003, 49 percent in 2004, 105 percent in 2005, 7 percent in 2006, and 68 percent in 2007; 2008 is expected to be an average or aboveaverage year. So far, the major storage reservoirs in the Upper and Lower Basins have provided the needed cushion to prevent widespread shortages, and have provided the stimulus for the states to enact new basin-wide reservoir management rules that should reduce the possibility of curtailments being needed in Colorado to meet interstate obligations.

The twin challenges of declining average flows and the enhanced probability of larger and more frequent droughts are being addressed by a variety of adaptation mechanisms. Of these two concerns, drought is the more familiar challenge, as is the solution: storage. However, while storage reservoirs can provide the buffer needed to smooth out flow variability across seasons and years, they are unlikely to boost system yields if longterm average streamflows decline, especially on a river like the Colorado that already can store roughly four full years of flow. This aspect of the climate change challenge calls for a much more diversified suite of adaptation strategies based on a combination of augmenting supplies and reducing demands, perhaps through mechanisms as diverse as transbasin imports; desalinization; weather modification, such as cloud seeding; efficiency im-

provements; pricing mechanisms; and shifting water among uses and users. Many examples of these mechanisms can now be found in the Colorado basin, at both the interstate scale and within particular states, including Colorado. Current drought conditions and the growing understanding of climate change dramatically accelerated these processes.

The Special Issue of Water Rights Timing Another issue with an interstate component is the shift in timing of water flows in response to climate change.

Colorado is a signatory to five interstate compacts—on the Arkansas, La Plata, Rio Grande, and South Platte rivers, and Costilla Creek—that feature apportionment formulas using specific calendar dates. These dates are usually in the spring and fall, and are used to distinguish between key water management seasons (such as the irrigation and storage seasons) and between periods of restricted versus unrestricted use.

With every passing year, the formulas may become more out of step with the natural hydrograph and with patterns of water demand. A similar situation exists with many important intra-state water rights, including water rights purchased by cities from farmers. While this aspect of the climate change/water nexus has not been highly problematic yet, it is a reminder that climate change affects water systems in multiple ways, and solutions must address both the institutional and physical infrastructure of water management. q

Citizen’s Guide to Colorado Climate Change

31

No one knows for sure what will happen to Colorado’s water supply as climate changes.

By Lori Ozzello

32

Daily headlines declare the latest discoveries and observations about global warming’s effects, from melting glaciers to changes in upland bird hunting to proposals of how to manage forests, fires and energy production in new ways.

Since the 2002 drought, water managers are acutely aware that the past is no certain indicator of the future.

Amid climate models, data and theories, many scientists say climate is changing and the effects may dramatically alter Colorado’s water outlook.

The models present “a thousand realizations,” says Joel Smith, vice president of Stratus Consulting and

a modeling grid.

Why not make the grids smaller?

“If we have a grid and cut it in half, the computation goes up by a factor of eight,” Yates explained. For example, say calculations that take a day.

Grids half the size would tie up a computer for eight days. To get the grids down to a better representative size, scientists would need 20 times the computing power now possible.

“The models are getting better, but we still don’t know the (answers) around precipitation,” said John Roach, a Trout Unlimited aquatics specialist. “We’re pretty confident about air temperature.”

former deputy director for the EPA’s Climate Change Division. Stratus analyzes potential climate change issues.

David Yates, project scientist at the National Center for Atmospheric Research in Boulder, echoes Smith’s sentiment.

“No one really knows for sure,” said Yates. He consults with Colorado Springs Utilities, Denver and Aurora about their contingencies for managing their water supplies. “We don’t know. Honestly.

“I’ve heard people say Lake Mead will be dry by 2025. It’s absurd.”

While some data can be plugged into models, some others elude analysts.

“Water vapor is very difficult to represent in the model,” says Yates. Add that to Colorado’s Rocky Mountains, wind and the limitations of computers and models, and the results are less than definitive.

For instance, computer modeling study areas are divided into 150 square kilometer parcels. That’s slightly more than 37,000 acres or nearly 58 square miles. By comparison, Denver International Airport sits on 53 square miles, making it slightly smaller than one square on

The models indicate a temperature increase in the state, along with changes in precipitation.

“I recognize there is something changing,” said Marc Catlin, Uncompahgre Valley Water Users’ general manager.

“There’s more wind and it’s longer and harder. We’re getting a dusty wind from the desert. When it’s on the mountain, snowmelt starts two weeks early.”

In the winter of ’08, Catlin said the area received more snow than it had in 15 years. As spring approached, many in the Uncompahgre Valley, including Catlin, expected flooding. Instead, the weather was hot for a week, then cooled off. The pattern repeated itself “bringing the runoff off in steps.”

By June, water users were getting their full allotments, but with humidity below 10 percent and a 10 mph wind, “the wind was sucking the moisture out.” Low humidity plus heat stressed feed corn crops.

More people pay attention to weather forecasts since climate change hit the mainstream media, Catlin said.

More irrigators are “putting their

Colorado Foundation for Water Education

ditches in pipe” to cut evaporation and farmers who flood irrigated for years are now trying sprinklers and drip irrigation.

What Catlin observed parallels what Stratus’ Smith and others have already discovered.

“The availability of water is shifting,” said Smith.

Anecdotal evidence is abundant on the state’s river systems, but except for the Colorado River, extensive scientific information about climate change effects is slim. As a state, Colorado does have a couple advantages: a well-established water appropriation system and experienced

researchers say the West is warming at twice as fast as the global rate.

What does that mean for Colorado’s other rivers?

So far, climate researchers are not investigating Colorado’s other major rivers—the South Platte, Arkansas and Rio Grande.

Denver Water has conducted some “crude” modeling on its water supply.

With a 2 degree Fahrenheit increase the model showed a 7 percent decline in supply. With 5 degrees, the decline doubled to 14 percent.

“We know we’re vulnerable to temperature changes,” said Marc Waage, Denver Water’s manager of water re-

The group plans to develop two hydrological models, Waage said, so researchers can compare variations.

The project, conducted by consultants in collaboration with the ninemember group, is expected to take about a year.

“As far as I know this is the first region in the U.S. to do this,” Waage said.

One component of the project is to standardize scenarios through the models so water managers are all “on the same page.”

The CWCB, he said, wants to learn whether hydrology models can be developed regionally, which would be more economical. The models un-

water managers.

“Prior appropriation has kept the rivers alive,” Catlin said.

And the knowledge water managers have about how to respond to supply fluctuations puts them in a position to deal with changes on the short and long term.

But eventually, they’re going to need more.

The Colorado River, on which an estimated 30 million people depend, is under intense study to forecast hydrologic and climate change effects.

In 2006, the U.S. Bureau of Reclamation brought together a group of scientists. The results, “The Climate Technical Group Report,“ found detailed information is necessary to improve Reclamation’s “decision support framework,” which includes climate modeling and applying the data. The report is an appendix to the final Environmental Impact Statement for operating guidelines in the Colorado River’s Lower Basin. Other

source planners. “We need new models. We have a range of projections to look at, but no real agreement.

Denver Water initiated a Front Range hydrology project to collect climate change information and adapt it to determine what the effects on water supply might be.

Denver Water; the Northern Colorado Water Conservancy District; Colorado Water Conservation Board; the Water Research Foundation, formerly the American Water Works Association Research Foundation; the Western Water Assessment; and the cities of Aurora, Boulder, Colorado Springs and Fort Collins are collaborators on a Front Range hydrology project intended to determine the possible effects of climate change projections on streamflow.

First, though, there’s one big hurdle: The models illustrate climate change scenarios, but “they don’t have a model to convert (that) data to projected streamflow changes,” said Waage.

der development will “have a range of projects to look at.”

When the results are in, said Waage, the participants can plug the data into their own allocation models.

“Once we have a model, we can plug information into a water allocation model and then into water rights.”

Then water managers will face the task of incorporating “deep uncertainty into water planning.”

Denver Water and others have taken pages from the oil and financial companies to learn how to weave a water resource plan from multiple sources of information and possibilities. That means revamping the way water planning has been done in the past.

Still, climate change research competes for money with water managers’ day-to-day concerns, such as water quality and how to balance growth and resources.

The key, Waage said, is to “keep options open and build in flexibility. Hydrology models are the key step.” q

Citizen’s Guide to Colorado Climate Change

33

P

redictions about how climate change will affect precipitation patterns are uncertain, but we can reasonably anticipate the results of warmer temperatures and longer growing seasons on agriculture.

Earlier snowmelt will significantly alter irrigated agriculture since Colorado farmers usually need the bulk of irrigation water in mid to late summer to finish crops. If we only consider the impact of higher temperatures and a greater number of frost-free days during the growing season, we can anticipate threats and benefits to crops and livestock and a drop in irrigation water supply.

Cool temperatures and lack of precipitation are most limiting to agriculture in Colorado. Warmer weather can be offset by adapting management, among other things. And cow-calf and feedlot operators in Colorado may realize a net gain by climate warming, at least in the short term. A cold winter hampers calves’ weight gain and increases calving mortality. A warmer climate means longer growing/grazing seasons and a shorter hay feeding season.

Ag’s Impact on Climate Early Anglo explorers such as Maj. Stephen Long dubbed eastern Colorado’s plains “The Great American Desert”. When the transcontinental railroads bisected the state in the mid-1800s, gold fever, settlement and the Homestead Act of 1862 spawned a new popular view that “rain follows the plow.” Corporate interests and other promoters told would-be settlers that if enough of the prairie was broken out of sod and planted to crops, the climate would change.

And it did, with wetter than average decades in the 1870s and ’80s. Influen-

34

Potential Ag

Impacts

from Climate

Change

By Reagan Waskom Director, Colorado Water Institute Colorado State University

tial scientists of the time—for example, University of Nebraska-Lincoln professor Samuel Aughey—theorized that turning over the soil would keep rain out of rivers and leave more for plants to transpire, where it could fall from the atmosphere again as rain. In 1886, the Omaha Daily Bee reported that increased rainfall generally followed railroad and telegraph line construction.

It was just a matter of time before drought returned to the Great Plains in 1887 and continued to bankrupt sodbusters through the Dry ’90s. The popular idea that human settlement brought beneficial climate change was abandoned.

Meanwhile, irrigated crop production expanded rapidly across Colorado as transmountain diversions, then reservoirs, then groundwater pumping, steadily increased water supply dependability. Today, approximately 5 percent of the land area of Colorado is irrigated, creating microclimates that favor crop production.

Some atmospheric scientists have observed that widespread adoption of irrigation has altered climate on a local to regional scale. [e\

A warmer climate could be good news and bad news for agriculture. The benefits: longer growing and grazing seasons, and less stress on calves during the winter. The drawbacks: crops at risk for heat stress, increased invasive species, earlier nectar flows that could affect pollination.

The Great Plains of the central United States currently represent 25 percent of the total U.S. irrigated lands and produce much of our food, feed and fiber. The Ogallala Aquifer lies beneath it and provides a great case study for climate adaptation. A clear temperature gradient exists from north to south and a precipitation gradient occurs from west to east across this region. Crops and livestock are successfully produced across these gradients by adapting management practices, crop and livestock species,

Colorado Foundation for Water Education

genetics, and other factors.

Irrigation helps offsets higher temperatures and lower precipitation. Smaller scale precipitation and temperature gradients are apparent across Colorado. Lack of precipitation and cool temperatures—not the presence of high temperatures— most often limit productivity. From Walsh to Holyoke, a 4.5 F summertime high temperature gradient can be seen now, with a corresponding growing degree unit increase. Interestingly, average grass evapotranspiration over the same gradient changes by less than 5 percent, or about 1 percent per degree F increase.

altered growing conditions harm the competitive advantage currently enjoyed by specialty crop growers. Irrigation may get hit from two sides: Earlier runoff would hinder irrigated agriculture if additional in-channel storage isn’t available and municipalowned irrigation supplies leased to farmers may not be available.

More evaporation from reservoirs, increased snow sublimation, earlier runoff, reduced groundwater recharge and greater irrigation water demand indicate water supplies will be more

[e\ Based on mesoscale modeling studies—and confirmed in some cases by surface observations—the expansion of irrigation in areas with extensive irrigation has increased local midsummer humidity; decreased local daytime temperatures; and, possibly increased nighttime mid summer temperatures.

Irrigated agriculture also created daytime “sea-breeze” type wind patterns, where winds blow outward from cooler irrigated cropland areas towards adjacent hotter dryland areas. This only happens when regional winds are very light. Some believe the crop breezes could create convergence areas that might favor cloud and possibly thunderstorm development over the adjacent dryland areas, but this is unproven. Forecasters assume the combined effect of higher humidity and local convergence zones will lead towards greater midsummer precipitation near areas of extensive irrigation.

Some other possibilities: Increased crop and non crop evapotranspiration will alter the basin scale water balance. Localized markets and processing industries may be affected if

limited and demand will be greater as temperatures rise. If precipitation patterns also change unfavorably for Colorado, the impacts will multiply.

Climate Change and Crops Crop producers face the triple threat of increased evaporation of snowpack and surface water, decreased runoff and recharge, coupled with increased crop evapotranspiration and consumptive use. Crops may also be at risk for heat stress during pollination and maturation, which can affect both yield and quality.

The up side: Scientists find elevated CO2 levels increased plant growth in labs and greenhouses. And, the warmer temperatures mean more frost free days, an advantage for growers in areas subject to early frost or short growing seasons.

In the midst of warmer temperatures, weeds, invasive species, insects

and diseases may spread. And pollinators—mainly honeybees—may be affected. Climate change, say NASA scientists and ecologists, could disrupt the relationship between plants and bees. A network of beekeepers and scientists found that in Maryland the peak nectar flow occurs four weeks earlier in the spring than it did in the 1970s. They hope to expand the network nationally.

Pollinators in general have a cascading effect on the food industry. A Cornell University study found that bees annually pollinate an estimated $14 billion worth of crops.

Livestock On the other end of the spectrum, weedy and invasive species likely will increase range and pasture competition, creating management headaches for livestock producers. Native range forage quantity and quality will change. Low value crop acreage— hay and grain for example—may be lost either because of water shortage or the transfer of crops to ethanol or biodiesel, reducing feeding industry competitiveness.

Shade and water may mitigate the possibility of increased summer heat stress on livestock during prolonged 90-degree plus temperatures.

Warmer temperatures and milder winters carry one advantage for livestock: the possible benefit of improved weight gain during the winter and better calf and lamb survival rates.

Adaptation by growers and improved genetics will sustain Colorado’s ag productivity. Agriculture can adapt, at least in the short term, to increasing temperatures and may even benefit by expanded growing areas, longer cropping seasons and easier winters on livestock. Commodities not currently viable in Colorado may become feasible with milder winters. The most serious crop concerns are related to higher evaporative demands coupled with reduced precipitation. q

Citizen’s Guide to Colorado Climate Change

35

Climate affects all terrestrial and aquatic ecosystems in Colorado, and over the long term, plants and animals adapt. In the short term, fires, increased attacks by insects and invasive plant species, and higher temperatures are changing familiar landscapes.

Annual and seasonal changes in climate will alter the mountain snowpack, plant flowering, animal breeding, seasonal migrations, plant and animal species’ ranges, and ecosystem productivity and processes. Further, the changes in the atmospheric chemistry, such as the increases in carbon dioxide concentrations, also influence plant growth and plant species composition.

Recently observed changes in plants and animals are apparent in the timing of plant phenology; animal breeding, nesting behaviors and hibernation; as well as geographic distribution. Whether these changes are successful adaptations to climate change depends on many connections within plants, animals and ecosystems, the human influences on the landscapes, and the rate at which climate changes.

The changes in climate and the ecological effects will probably be gradual and abrupt. Gradual changes in temperature will likely influence annual events, such as when flowers bloom. Birds may begin to nest earlier. Abrupt changes could include the coincidence of drought, water stress on trees and insect outbreaks. For instance, in northern New Mexico over a recent two-year period, large areas of mixed conifers died.

By Linda Joyce Quantitative Ecologist and RPA Climate Change Specialist, Rocky Mountain Research Station, USFS

Phenology—the recurrence of annual events that correlate with climate.

Ecosystem—a community of plants, animals and microorganisms that constantly interact.

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Ecosystems The state’s ecosystems vary from the grasslands on the eastern plains to the forests and alpine tundra that cover the Rocky Mountains in central Colorado to shrublands, woodlands and forests that cover the western landscapes.

In the mountains, vegetation gradually changes in species from the montane forests, to the subalpine forests, and finally to tundra as elevation rises.

Grassland ecosystems are dry. Precipitation comes mainly in the months of March through May and June. The grasslands will see increased temperatures throughout the year. The growing season will lengthen, with severe frosts occurring earlier in the fall and later in the spring.

Precipitation projections are uncertain. With temperature increases, there is likely to be more stress on the plants even if precipitation remains at historical levels. Colorado grasslands adapt for drought, shifting species composition to plants better suited to warmer temperatures and less precipitation. For example, under drought, the vegetation adapts by shifting to the shortgrasses of blue grama and buffalo grass. But precipitation pattern changes may influence species composition in new ways.

Ongoing experiments in grassland ecosystems explore the impact of nearly double the atmospheric concentration of carbon dioxide on the grassland. After four years, the plant response is evident and varies greatly by species.

Woody shrubs, such as fringed sage, appear to increase in productivity more than the native grasses. The native grasses appear to decline in palatability and digestibility, suggesting a decline in the future quality of forage for wild and domestic grazers, such as pronghorn and cattle.

Colorado Foundation for Water Education

Montane and subalpine forest ecosystems cover the lower to higher slopes of the Rocky Mountains. Ponderosa pine is predominant in the montane forest. Subalpine forests can include lodgepole pine, subalpine fir, Engelmann spruce and limber pine.

Climate change is likely to result in warmer and earlier springtimes, and warmer autumns and later frost. Most of the precipitation comes in the form of snow; but under a changing climate, some of this precipitation will come as rain in the fall and spring.

Colorado and its ecosystems depend on the snowpack to store water and gradually release moisture throughout the spring. Earlier melts and runoffs may mean a longer growing season with less moisture and greater moisture stress in summer and fall. Stress in trees opens the possibility for greater impacts from insects and disease. If the climate is drier, then the possibility exists for grassland and shrubland ecosystems to move into the montane forest and for the montane species to move into the elevation previously occupied by the subalpine forests.

Alpine tundra, the Rocky Mountains’ highest ecosystem, is covered by snow for long periods of time; but snow distribution is highly influenced by topography and wind. Warming temperatures and changes in the snow to rain occurrence will likely alter this distribution of snow on the landscape. Experiments manipulating the snow distribution show that plant species composition is very sensitive to snow distribution changes.

Under a changing climate, snowmelt would occur earlier, exposing the vegetation to sunlight and warming temperatures, which also portend the possibility of trees moving into the alpine. Such projections for the areas around Aspen suggest that the ski season will start later and end earlier, the possible need for increased snow-making and potential conflicts with agriculture for water.

Disturbances Many of Colorado’s ecosystems are sensitive to climate. Warm and dry conditions mean more fires. An analysis of the recent precipitation

and temperature records in western United States suggests warmer, drier conditions have already resulted in longer fire seasons and fire at higher elevations, in the subalpine forests.

Similarly, studies on bark beetles, such as the mountain pine beetle, show the beetles’ population increases with warmer temperatures. The extreme winter cold that kills bark beetles hasn’t happened. Instead, beetles have thrived, suggesting that under a warming climate, bark beetles and greater epidemic attacks will increase.

Weather and climate strongly influence insects and fire, but so does human activity. The current bark beetle epidemic in Colorado is in large areas of trees of similar age; and the legacy of fire suppression in the western United States left landscapes with dense stands. Future climate change impacts will interact with the human effects on the landscape.

Invasive Species A species is considered invasive if it is non-native to the ecosystem under consideration; and if its introduction causes, or is likely to cause, economic or environmental damage, or to harm human health.

Colorado has identified a number of noxious plant species. The Colorado Commissioner of Agriculture— in consultation with the state noxious weed advisory committee, local governments, and other interested parties—develops and implements state noxious weed management plans designed to stop the spread of invaders, such as the yellow starthistle (centaurea solstitialis) Canada thistle (cirsium arvense), leafy spurge (euphorbia esula), and spotted knapweed (centaurea maculosa). These species could benefit from climate change.

Researchers explored the response of six invasive weeds—Canada thistle, yellow starthistle, leafy spurge, spotted knapweed, field bindweed, and perennial sowthistle—to concentrations of carbon dioxide from the beginning of the 20th century to the end of the 21st century. Increases in atmospheric carbon dioxide from the early 20th century to the present stimulated invasive plant biomass by an average of 110 percent, raising the possibility that more atmo-

spheric carbon might be partly responsible for the spread of invasive weeds during the 20th century.

The trend is expected to continue: Likely future concentrations of carbon dioxide in the atmosphere will stimulate invasive plant biomass in the six species studied by Ziska (2003) by an average of 46 percent, with the largest response for Canada thistle. While studies like this one are important to increase our understanding of invasive plants’ response to increased carbon dioxide concentration, little is known about many invasive species’ life history, growth or response to climate change.

Wildlife Colorado wildlife includes many species of birds, mammals, reptiles and amphibians. The State Wildlife Action Plan includes 205 Species of Greatest Conservation Need. The gravest threats to Colorado wildlife include habitat conversion; infrastructure and other resource demands from a growing Colorado population; recreation; invasive and/or exotic species; and coordination, funding and information gaps.

Climate change is likely to affect wildlife, too, through habitat changes, such as interaction with invasive species and changes in the availability of cover and protection from temperature extremes. Already, the yellow-bellied marmot comes out of hibernation nearly three weeks early, a response to the warmer air temperatures.

Climate change could alter the habitat for Colorado’s cool- and coldwater fish, including the endangered greenback cutthroat trout. Competition with non-native fish species already reduced their territory.

Future vegetation pattern changes will fragment habitat and open the possibility of novel combinations of plant species co-existing. Such landscape changes will affect the wildlife habitat suitability as well as the potential to migrate across a different landscape to seek habitat.

Snow Dependent Species Asynchrony is defined as the relation that exists when things occur at unrelated times. Plants, animals and ecosys-

Citizen’s Guide to Colorado Climate Change

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Asynchrony is more than snowmelt. It’s a pattern. tems have evolved over time to have dependent relationships, such as the birth of young to coincide with the availability of food. Climate change could unravel these close relationships.

Asynchrony is more than snowmelt. It’s a pattern.

An example: At the Rocky Mountain Biological Laboratory near Crested Butte, the timing of snowmelt has not changed in the two decades it’s been studied. Vegetative growth does not occur until the snow has melted, so the resulting appearance of green vegetative material has not changed much.

Temperatures have risen over the last several decades. Consequently, hibernating animals, such as marmots, come out earlier, when there is still snow. Vegetation is sparse and little food is available. This type of asynchrony could increase stress on marmots. Other types of asynchrony include migrants arriving earlier and their food source, insects, having already hatched and flown. Asynchrony is likely to cause surprises.

Adaptation Options Plants and animals will seek to adapt to climate changes as they have in the past. The challenge may be the speed of climate change and the rate plants and animals can adjust. Human activity confounds landscape features and that may affect plants and animals’ ability to migrate to new habitat. Minimizing the stress may improve ecosystem health and resilience in the face of a changing climate.

Colorado landscapes are subjected to a variety of current stressors, such as air and water pollution, habitat fragmentation and invasive species, as well as the legacy of past land management. A focus on minimizing stresses may improve the ecosystem’s resilience and improve its health. q Asynchrony—a lack of synchronism or coincidence; the relation that exists when things occur at unrelated times

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Additional Reading

Aspen Global Change Institute. 2006.

“Climate Change and Aspen: an assessment of impacts and potential responses.” Aspen Global Change Institute, Aspen, CO. Baron, Jill S. 2002. “Rocky Mountain futures: an ecological perspective.”

Washington, D.C.: Island Press Bentz, Barbara. (in press). “Bark Beetle Outbreaks in Western North America, Causes and Consequences.” Utah State University, Utah.

Bosworth, D., Birdsey, R., Joyce, L., Millar, C. In press. “Climate change and the nation’s forests: Challenges and opportunities.” Journal of Forestry.

Colorado Division of Wildlife. 2006.

“Colorado’s Comprehensive Wildlife Conservation Strategy.” Colorado Division of Wildlife.

EPA. 5/21/2007. “Climate Change and Colorado.” EPA. http://yosemite. epa.gov/oar/globalwarming.nsf/ UniqueKeyLookup/SHSU5BPPNK/$File/ co_impct.pdf Inouye, D.W., Barr, B., Armitage, K.B., Inouye, B.D. 2007. “Climate change is affecting altitudinal migrants and hibernating species.” PNAS 97:1630-1633 Joyce, L.A, Blate, G., Littell, J., McNulty S., Millar, C., Moser S., Neilson R., O’Halloran, K., Peterson D.L. In press.

“Adaptation options for climatesensitive ecosystems and resources: National Forests.” Synthesis and Assessment Product 4.4, U.S. Climate Change Science Program. 151 pgs.

Kruger, F.A., Fielder, J., Meaney, C.A. 1995. “Explore Colorado: A naturalist’s Notebook, Denver Museum of Natural History.” Westcliffe Publishers Logan, J., Powell, J. 2001. “Ghost forests, global warming, and the mountain pine beetle.” American Entomologist 47: 161-172 Morgan, J.A., Derner, J.D., Milchunas, D., Pendall, E. 2008. Management implications of global change for Great Plains rangelands. Rangelands 30(3):18-22.

National Assessment Synthesis Team.

2000. “Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change.” Overview. Report for the U.S. Global Change Research Program. Cambridge University Press, Cambridge UK. 154 p.

National Assessment Synthesis Team.

2001. “Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change.” Foundation Report.

Report for the U.S. Global Change Research Program. Cambridge University Press, Cambridge UK Ojima, D. S., J. M. Lackett, and the Central Great Plains Steering Committee and Assessment Team. 2002. “Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change—Central Great Plains.”

Report for the U.S. Global Change Research Program. Colorado State University. 103 pp.

Joyce, L.A, Blate, G., Littell, J., McNulty S., Millar, C., Moser S., Neilson R., O’Halloran, K., Peterson D.L. 2008.

National Forests. IN: Julius, S.H., J.M. West, J.S. Baron, B Griffith, L.A. Joyce, P. Kareiva, B,D. Keller, M.A. Palmer, C.H. Peterson, and J.M. Scott.

Preliminary review of adaptation options for climate-sensitive ecosystems and resources. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. U.S. Environmental Protection Agency, Washington, D.C.

Colorado Foundation for Water Education

Increased carbon dioxide levels affect native range plants (background), including blue gramma (above), and encourage the spread of noxious weeds.

Health concerns part of climate change discussion

By Gregg Thomas and Carrie Atiyeh Department of Environmental Health, City & County of Denver

Overview During the 2002 drought, Colorado got a preview of what some climate change effects might be: Less oxygen in streams, stressed aquatic life and lower flows that lead to a host of other problems.

Climate change forecasts may have serious impacts to the environ-

ment as a whole and air and water quality, specifically. Public health will feel the direct impacts.1,2,3 As the Centers for Disease Control and Prevention detail in the chart below, the potential public health impacts related to climate change are diverse and significant, affecting various populations.4

160% 140%

Percent Increase Over Non-Drought Years

120% 100% 80% 60% 40% 20% 0%

Temperature

TDS

Ammonia

Nitrate

Phosphorous

E. coli

Source: City and County of Denver, Environmental Quality Division

Weather Event

Health Effects

Populations Most Affected

Heat waves

Heat stress

Extremes of age, athletes, people with respiratory disease

Droughts, floods, increased mean temperature

Vector-, food- and water-borne diseases

Multiple populations at risk

Increases in ground-level ozone, airborne allergens, and other pollutants

Respiratory disease exacerbations (COPD*, asthma, allergic rhinitis, bronchitis)

Elderly, children, those with respiratory disease

Extreme weather events, (rain, hurricane, tornado, flooding)

Injuries, drowning

Coastal, low-lying land dwellers, low SES*

* COPD: Chronic Obstructive Pulmonary Disease; SES: Socioeconomic Status Source: Centers for Disease Control and Prevention, Policy on Climate Change and Public Health

Impacts of Climate Change on Water Quality In Colorado and the western United States, climate change is projected to have serious effects on water quality and quantity, including decreases in snowpack, snow melt earlier in the spring, and reduced stream and river flows in the summer.5,6,7 Subsequent water quality impacts in streams and rivers could include increased temperatures, less oxygen, lower water levels and additional stress to aquatic life.

Droughts are forecast to be longer and more numerous.

We have already seen signs of such impacts. Between March 2002 and January 2003 poor precipitation in Colorado’s mountains resulted in significantly lower than normal water flows in the South Platte River. Mean monthly flows in the South Platte River during the drought ranged between 18 and 56 percent of the mean monthly flows observed between 1998 and 2007, a startling drop in water quantity. Lower stream flows in an urban area translates to less dilution capacity for and higher instream levels of pollutants.

South Platte River data, collected during the drought, can be used to help determine the potential influences of climate change on local water quality. Denver Department of Environmental Health analysts examined factors including temperature, total dissolved solids, ammonia, nitrate, phosphorous, and E. coli data to determine if there was any difference in measurements collected during drought and nondrought years. Levels of E. coli are monitored because some strains Total Dissolved Solids—a measure of a range of pollutants, including salt, selenium and heavy metals, dissolved in water.

Citizen’s Guide to Colorado Climate Change

39

can sicken people. As shown in the graph below, all of the levels except E. coli were significantly higher during the drought then at other times.

The results of the analysis of E. coli data were inconclusive Increased water temperature promotes algae production, leading to decreasing oxygen levels and serious consequences for fish. The analysis suggests some weather extremes caused by climate change, such as drought, may have negative effects on water quality in the South Platte River. Levels of all of the measured factors were significantly higher during the drought than at other times.

Impacts of Climate Change on Air Quality Ground level ozone pollution, or smog, is one of the most harmful public health effects climate change will have on air quality. As of November 2007, Denver is in violation of the EPA national ambient air quality standard, or NAAQS, for ozone, 80 parts per billion.8 Other areas of Colorado – such as Colorado Springs, Aspen and the San Juan basin—may violate the recently revised EPA standard, 75 ppb, within the next few years. Boulder, Greeley and Fort Collins are already included in Denver’s non-attainment area. Grand Junction lacks long-term monitoring, but if or when data is available, the West Slope city may also be in violation.

Sensitive populations with respiratory illnesses, such as asthma, are most susceptible to smog. A recent study by the National Academy of Sciences’ National Research Council found “short-term exposure to current levels of ozone in many areas is likely to contribute to premature deaths.”9 The EPA’s risk assessment document provides documentation of substantial reductions in premature total, respiratory and cardiorespiratory deaths, hospital admissions for respiratory admissions, asthmatic symptoms in moderate/severe asthmatic children, and lung function decrements in children at an ozone NAAQS level as low as 64 ppb.10 The forecast for hotter and drier summers is expected to increase urban ozone pollution since sunlight and heat are key components to ozone formation. Reducing harmful air emissions that cause ozone pol40

lution and greenhouse gases will improve local and regional air quality and public health.

Reduce and Improve While climate change is a global problem, we all must contribute to the solution. Individual, local, state, and national actions are necessary to reduce the impacts of climate change.

Personal lifestyle choices have an important effect on climate change as well as public health. By supporting sustainable, climate-protecting policies and actions, and changing consumption habits, individuals acting together can make a difference. The City and County of Denver’s Climate Action Plan11 is a useful framework for local governments attempting to achieve greenhouse gas reductions within their span of control.

Transportation accounts for a significant amount of most individuals’ impact to local air quality and climate.

Choosing alternative transportation, such as mass transit, biking or walking, harmful emissions are kept out of the air and individual health benefits through increased exercise. When personal automobiles are necessary, choosing a car that gets fuel economy as high as possible will help reduce our carbon footprint and smogcausing emissions.

Coloradans also have the option to choose clean, renewable energy generated by wind and solar. Since the majority of Colorado’s energy is supplied by fossil fuels, such as coal and natural gas, switching to emissionfree and climate-friendly renewable energy in residential homes and businesses can significantly reduce the environmental impacts from energy production and protect public health through cleaner air and water. q

References

1. Frumkin, Howard, et al., Climate Change: The Public Health Response, American Journal of Public Health, March 2008, Vol 98, No. 3.

2. Patz, Jonathan, et al., Impact of Regional Climate Change on Human Health, Nature, Vol 438, November 17, 2005.

3. Patz, Jonathan, Testimony Before the Select Committee on Energy Independence and Global Warming, April 9, 2008.

4. Centers for Disease Control and Prevention, Policy on Climate Change and Public Health. Available at: http://www. cdc.gov/ClimateChange/policy.htm.

5. US EPA, Climate Change—Health and Environmental Effects; Possible Water Resource Impacts in North America, 2007. Available at: http://www.epa. gov/climatechange/effects/water/ northamerica.html.

6. IPCC, Climate Change 2007: Impacts, Adaptation, and Vulnerability, 2007.

Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Parry, Martin L., Canziani, Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson, Clair E. (eds.)]. Cambridge University Press, Cambridge, United Kingdom, 1000 pp.

Available at: http://www.ipcc-wg2.org/ index.html.

7. CU-NOAA, Climate Change, Water Quality and the Future: Lessons from the Western Water Assessment, Presentation at Western Coalition of Arid States, February 23, 2006. http://wwa. colorado.edu/about/homepages/udall/ udall%20westcas%20v2.pdf.

8. US EPA, Denver’s Ozone Designation.

Available at: http://www.epa.gov/region8/air/denverozone.html.

9. National Academies of Science, Link Between Ozone Air Pollution and Premature Death Confirmed, April 22, 2008. Available at: http://www8. nationalacademies.org/onpinews/ newsitem.aspx?RecordID=12198.

10. US EPA, Ozone health risk assessment for selected urban areas. EPA 452/R-07-001. 2007.

11. City and County of Denver, City of Denver Climate Action Plan, October 2007. Available at: http://www.greenprintdenver.org

Colorado Foundation for Water Education

Colorado Committed to Energy Conversion

By Tom Plant

Director, Governor’s Energy Office

Ritter announced a climate change year—at that rate we would double Renewable Energy Bill goal to considerably reduce carbon our 2005 levels of consumption by

is definitely a part of Colorado’s future.

Fossil fuels are currently critical to our economy and lifestyle. For example, coal provides a large portion of our electricity; petroleum primarily powers our vehicles; and natural gas often heats our homes.

But, fossil fuel CO2 emissions contribute to climate change. One way to reduce the impacts of climate change without affecting our economy and lifestyle is to convert to renewable energy whenever it makes economic sense.

Thanks to Colorado voters, our state has already committed itself to substantial renewable energy production, the most important action needed to control climate change.

A 2004 citizen initiative requires electric utilities to use the sun, wind, geothermal, biomass and flowing water to produce power. Lawmakers responded in 2007 with measures designed to make Colorado a renewable energy leader. Renewable energy and conservation to reduce electricity consumption help the state economy while reducing carbon emissions that contribute to global warming.

In November 2007, Colorado Gov.

emissions over the next four decades. In the midst of the policy shift, technology and sustainable resource advances in wind, solar and geothermal energy continue to expand.

Consider the challenge: The governor called for a 20 percent reduction in carbon emissions in Colorado below 2005 levels by 2020, and by 2050, the goal is 80 percent below 2005 levels. The announcement marked a profound shift in policy for the state of Colorado.

We don’t know what technologies will develop in 15 years, never mind 45. A changing energy paradigm requires successful industries to reevaluate the services they provide, and this is already beginning to occur in Colorado.

Today we have the ability to drive the decisions, the technologies and the outcomes of the future with a bold but practical approach. The Climate Action Plan provides a blueprint to base policy and business decisions.

While the plan presents a challenging goal within the current climactic experience, projections under a business-as-usual scenario suggest energy use will increase by 2 percent each

2040, only 10 years before our goal of an 80 percent reduction from those same 2005 levels.

A very real possibility exists that our assumptions, based on our current climate experience, is intrinsically flawed. Imagine the changing energy paradigm in an era of climate change:

The Cedar Creek wind farm east of Grover is expected to generate 300 megawatts of electricity annually—enough to power 90,000 average-sized homes for a year.

Insolation—solar energy striking the earth or any other planet.

• If warmer summers continue, will peak loads increase?

• Will the heating requirements in the winter be reduced?

• Will reductions in water availability reduce hydropower production potential?

• Will insolation ratings change perceptibly to allow for greater solar production potential throughout the state?

• What will be the effect on wind production?

• What will the impacts of a changing economy—from fewer ski days to less water for agriculture—have on electrical and transportation demand?

• Will changes in the economy reflect themselves in a reversal of growth trends?

Citizen’s Guide to Colorado Climate Change

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The answers to these and many other questions are unknown. But, for the purposes of discussion, consider one of the many dynamics of Colorado’s future as it relates to climate change— a reduction in water availability.

Recent estimates suggest that a changing climate may reduce the available water supply by as much as 10%, perhaps more, in the foreseeable future. Existing compacts, which guarantee a volume of water to downstream states, will have a profound effect on Colorado’s energy production systems.

Currently, our baseload resources are heavily dependent on water. Current traditional coal production methods consume approximately 500 gallons of water per mega-watt hour of production. Projections of demand increases by the Colorado Energy Forum reflect an increase in overall demand of 20,000 gigawatt hours between 2005 and 2020. That size of an increase in demand would require an additional 10 billion gallons, or more than 30,000 acre feet, of water per year if the demand were met through coal production.

Many look to nuclear to provide that baseload resource without the attendant CO2 emissions of coal. But when you look at the water impact, a similar load provided by nuclear energy would annually demand an additional 43,000 acre feet of water.

Hydropower resources provide approximately 11 percent of production in Colorado. With prolonged drought and diminishing reservoirs, a dramatic decrease in the capacity available from this baseload resource is possible as well.

Luckily, we have several options to address the concerns. While wind energy operates at a capacity factor—time in which the resource is actually producing electricity—of 35 percent and solar operates at 20 percent or less, the integration of these resources into the same renewable transmission network enables each to support the other and raise the overall available capacity.

Gigawatt—one billion watts Capacity Factor —the ratio of the actual output of a power plant over a period of time and its output if it had operated a full capacity of that time period.

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Colorado is talking with Wyoming and New Mexico to develop a multistate renewable transmission network to combine renewable resources from a diverse geographic area.

Wyoming wind actually produces at a time complementary to Colorado and New Mexico wind power.

Integrating geographically diverse resources into the same network offers the opportunity to maximize the effectiveness of each resource.

With an integrated, multi-state network of transmission, renewable energy generators can increase their potential markets. A network also frees Colorado from specific demands and load profiles.

Aside from wind power and the network possibilities, advancing solar technology may make it more available and less expensive.

Solar generation is in the midst of a transformative period, both from the distribution and utility scale production levels. New thin film technology promises tremendous advances in photovoltaic applications. Ascent Solar in Lakewood produces a thin film photovoltaic product delivered in rolls. It can be applied directly to a variety of surfaces, regardless of the geometry. In fact, Ascent recently signed a contract with a European roofing material manufacturer to provide a solar photovoltaic roofing product.

AA solar in Fort Collins has developed a thin film production process that is less costly. Primestar expanded on utility scale thin film applications with a new proprietary technology that will increase efficiency levels beyond what is currently available. All three announced plans to locate manufacturing facilities in Colorado.

Concentrated solar power, which uses thermal electric generation as opposed to photovoltaic generation, is also developing at a rapid pace.

Recent large scale contracts with western utilities are pushing the scale of these plants as well as leading to advances in thermal energy storage.

This will dramatically change the production profile of the plants, possibly providing as much as 12 hours of energy storage. A solar production process capable of delivering electricity on demand, regardless of the time of day, is very close at hand.

Until there are significant storage

developments, full scale development of our renewable resources will depend on the ability to even out production variabilities with traditional resources such as natural gas.

Fortunately, Colorado has significant resources to contribute to management of this load. In combination with renewable energy, natural gas represents a strong low-carbon bridge fuel alternative.

The nascent geothermal industry is starting to wake up in the United States.

Nevada has been a leader in geothermal production, but today there are a number of potential production sites in Colorado under investigation. An MIT study in 2007 ranked Colorado fourth in the country in potential geothermal production locations. The possibility of delivering a renewable resource at 80-90 percent capacity could transform the energy production portfolio of Colorado and the West.

Finally, Colorado has the opportunity to benefit from a resource that has no water consumption, has baseload capacity factors and is a fraction of the cost of coal or gas: energy efficiency.

Advances in electrical appliances and lighting continue to reduce per capita demand on the electrical grid.

Combined with advances in product technology, utilities will change how they manage loads and resources through evolutions in “smart grid” technology. Boulder was recently tagged as the world’s first “smart grid city” with a pilot project announced

by Xcel. This project will develop next generation utility management infrastructure and fundamentally alter the delivery of electricity. It takes full advantage of the ability to manage load demand and integrate distributed resources, including for the first time, plug-in hybrid electric vehicles capable of storing and delivering electricity to the grid during high demand periods.

Since the industrial age, we have produced and delivered electricity in much the same way. Advances in renewable energy technologies, price signals from traditional sources, changes in demand management, and improvements in building system design combined with attention to the impacts of climate change will fundamentally change the way we produce, consume and deliver electricity. q

Colorado Foundation for Water Education

By Lori Ozzello

Skiing in Colorado attracts natives and visitors by the millions every year.

Under idyllic conditions—azure skies, sunshine, fresh snow—enthusiasts schuss the days away and pump money into the state’s economy. Ski lovers will tolerate long drives, traffic bottlenecks, lift lines and escalating ticket prices for time on the mountain.

As common as the experience is to so many people, the grandchildren of Generation-Y may never know a day on the slopes. Although some scientists and climatologists say the state’s high elevation may protect skiing longer, ski industry officials say at some point, it won’t make economic sense.

Within a century, climate change may put an end to winter sports in Colorado. By the time that happens, though, says one ski official: “There will be more problems than not being able to ski.”

Auden Schendler, Aspen’s executive director of sustainability, first learned of climate change in 1990. Ten years ago, he joined Aspen’s staff to “take ideas that were theoretical and put them into practice.” He’s among a group of ski industry officials who have aggressively pursued green energy options and testified before Congress about the challenges ahead.

“What we’re doing is using the high profile nature of the business to drive policy change,” said Schendler. “That’s what we can do.”

On the mountain, the options are already diminishing. For decades, ski resorts augmented snowpack with artificially made snow. As

the climate changes, Schendler said, it “becomes exponentially more expensive as the nights get warmer. The (climate) models say that and it’s what we’re seeing.”

The ski season is a concern, as well, said Schendler. Historically, the season begins for most resorts in November and lasts through late April.

This, too, is changing.

According to a March 2008 National Resources Defense Council report, the Rockies’ snowpack dropped 16 percent between 1950 and 1999. NRDC documented “decreases in snowpack, less snowfall, earlier snow melt, and more winter rain … and reduced summer flows” throughout the West.

And over the last 40 years, records show runoff occurred earlier by an average of nine days. The shift means fewer ski days and early peak flows, and any loss can be devastating to an industry which relies on only about 180 days each year.

“When you look at skiing as a business to be in,” he explained, “if you shaved a week off in March, eventually it would make the business unfeasible.”

Schendler said his organization knows there are higher priorities.

“We’ve said that by the time you can’t ski at Aspen Mountain, there will be a lot more problems than not being able to ski,” Schendler said.

“The bigger issue: If climate does what we think, there will be some big economic impacts that will prevent (skiing). There will be changes in the national economy and coastal cities” that prevent recreation as it’s developed over the 20th and early 21st century.

Trends in snowpack loss—and the accepted climate change models—signal an array of obvious and subtle effects of a climate shift. From downhill skiing and snowboarding to hunting, fishing, rafting and bird watching, to traditional summer and fall games, climate changes are expected to affect them all.

Citizen’s Guide to Colorado Climate Change

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Mountain snowpack provides a crucial supply of water for millions of people in Western states. Farms, hydroelectric plants, energy extraction industries, aquatic life and an estimated one-fifth of the U.S. population depend on it.

The Colorado ski industry alone generates an estimated $1.7 billion in revenues, more than 100,000 jobs and a $1.5 billion payroll, states a recent report by the U.S. National Assessment of the Potential Consequences of Climate Variability and Change. Support industries—retailers and equipment renters, hotels, restaurants and travel agencies, among others—weren’t factored into the report.

“Even if you don’t like to ski, it’s an easy connection to make how many businesses will be affected by climate change,” said Geraldine Link, spokeswoman for the National Ski Area Association. “There’s only so much the 300-plus ski resorts across the country can do. It takes millions of people who ski and ride to make the difference.”

Link points to the industry’s investments in renewable energy—68 of the resorts nationwide buy offsets. Half of those depend entirely on green power.

No matter what the resorts’ power sources are and regardless of the sport, the beginning of the equation is snow.

The snowpack becomes the spring runoff that literally floats the rafting, kayaking, boating and fishing in the state, whether adventurers are in rivers or water parks or on a reservoir.

Irrigation greens the fairways, outfields and city parks, whether they are in Vail, Grand Junction or Lamar.

Hunting, fishing and wildlife watching generate more than $1 billion an-

nually. Pheasants Forever, Trout Unlimited, the American Sportfishing Association and others collaborated to publish a report, “Seasons End: Global Warming’s Threat to Hunting and Fishing” in April 2008.

The prairie pothole region, part of the Northern Great Plains and grasslands, contains shallow depressions left by receding glaciers. The potholes filled with water, forming wetlands for migratory birds. Many have been converted to agricultural use. According to the report, “The prairie pothole region could lose up to 90 percent of its wetlands, reducing the number of the continent’s breeding ducks by as much as 69 percent.”

By the end of the century, the group predicts as much as 42 percent of the current trout and salmon habitat will be lost, and half their populations may be gone, too. In the Rockies, the report said, “Bull trout will suffer reductions of up to 90 percent.”

Trout Unlimited stream ecologist John Roach admits it’s not a pretty picture.

For example, Roach said native razorback suckers, which are listed as an endangered species, are a warm water fish found in the Colorado River from Glenwood Springs to Grand Junction.

“If average water temperature increases, their range is likely to be extended,” he said. “At the lower end of their range, it may get so hot they can’t use it. The ideal thermal habitat shifts upslope.”

The possible effects on spawning are more complex.

“Some spawning is cued by temperature, some by hydrograph,” said Roach. What’s really going to matter

is whether the eggs and fry have a “good chance to survive. Part of the answer depends on habitat changes after spawning. If the conditions don’t change that much or the fry can (cope), it won’t be as much of a problem.

“Fish have evolved over a long time to match the current conditions.

The further you get from (the conditions) the greater the chance the fish won’t be able to deal with it. … Late seasons are going to become harder and harder on fish. The question is, how bad?”

Big game will feel the squeeze, too.

Pronghorn, elk and deer stand to lose habitat as the climate warms and trees and shrubs invade sagebrush ecosystems. At the same time, forests are likely to “climb to higher elevations, severely limiting the alpine habitats that support bighorn and other mountain sheep.” As fragmentation and winter range losses stack up, mule deer and elk populations in the West may drop.

The changes will affect birds of all sorts. Droughts caused by global warming could “devastate food sources for upland birds,” such as prairie chickens, grouse and pheasants. Hot dry temperatures are expected to disrupt breeding cycles, food supplies, such as insects, and “stunt the growth of vegetative cover, leaving broods vulnerable to predators.”

Turn in any direction, and an organization or group can list the predicted consequences of climate change on a Colorado sport.

Said Aspen’s Schendler: “This is a large problem. The solutions have to be to scale.” q

This is a large problem.

The solutions have to be to scale.

—Auden Schendler

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Colorado Foundation for Water Education

Colorado Foundation for Water Education 1580 Logan St., Suite 410 • Denver, CO 80203 303-377-4433 • www.cfwe.org

Mission Statement The mission of the Colorado Foundation for Water Education is to promote better understanding of water resources through education and information. The Foundation does not take an advocacy position on any water issue.

Board Members Matt Cook President

Justice Gregory J. Hobbs, Jr. 1st Vice President

Rita Crumpton

2nd Vice President

Wendy Hanophy Secretary

Taylor Hawes

Assistant Secretary

Chris Rowe Treasurer

Dale Mitchell

Assistant Treasurer

Becky Brooks Rep. Kathleen Curry Alexandra Davis Veva Deheza Jennifer Gimbel Alan Hamel Callie Hendrickson Lynn Herkenhoff Sen. Jim Isgar Chris Piper John Porter Rick Sackbauer Robert Sakata Steve Vandiver Reagan Waskom

This Citizen’s Guide to Colorado Climate Change (2008) is the eighth in a series of educational booklets designed to provide Colorado citizens with balanced and accurate information on a variety of subjects related to water resources. Copyright 2008 by the Colorado Foundation for Water Education. ISBN 978-0-9754075-8-5 Acknowledgements The Colorado Foundation for Water Education extends its gratitude to the team of reviewers who participated in evaluating the Citizen’s Guide on Climate Change. The authors and the Foundation are solely responsible for the contents of this Guide.

Authors Nolan Doesken, Colorado State Climatologist and Senior Research Associate, Colorado State University Dept. of Atmospheric Sciences Brad Udall, Director, CU-NOAA Western Water Assessment Roger Pielke, Sr., Senior Research Scientist (CIRES) and Senior Research Associate (ATOC) Lori Ozzello, Editor, Headwaters magazine Doug Kenney, University of Colorado, Natural Resources Law Center Reagan Waskom, Director, Colorado Water Institute, Colorado State University Linda Joyce, Quantitative Ecologist and RPA Climate Change Specialist, Rocky Mountain Research Station, USFS Gregg Thomas, Denver Environmental Health Carrie Atiyeh, Denver Environmental Health Tom Plant, Director, Governor’s Energy Office Editor Lori Ozzello Design R. Emmett Jordan All photographs are used with permission and remain the property of the respective photographers (©2008). All rights reserved.

Kevin Moloney—p.4, p.14, p.28, p.39. iStockPhoto.com—cover (4), inside cover (9), p.3 (top), p.7, p.9 (4), p.30, p.36 (2), p.40, p.43, back cover (top). William Green—inside cover. André Karwath—inside cover. NASA—inside cover, p.2. National Oceanic and Atmospheric Administration—inside front cover, p.13. R. Emmett Jordan—inside cover, cover overleaf, p.3, p.32 (2), p.34 (4), p.36, p.38 (2), p.41. ‘Tornado’ Tim Baker— p.12 (2). Denver Public Library, Western History Collection—p.12 (4), p.13 (2). Gustaf Nordenskiöld—p.12. Ed Kosmicki—p.44.

Staff Nicole Seltzer

Executive Director

MWH and the Colorado Water Conservation Board funded production of this Citizen’s Guide to Colorado Climate Change.

Kristin Mahrag

Educational Programs Associate

David Harper Office Manager

Citizen’s Guide to Colorado Climate Change

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CFWE Citizen’s Guide to Colorado Climate Change

A Few Predictions on How Coloradans Will Adapt Coloradans will adapt to climate change. We’ve always had to. We will expect our water managers to conserve well, plan well, and price water for what it’s really worth. We will expect our land use decision makers to shape communities that look and live great and water frugally. We will find our way to restore waterways we’ve wrecked in the past.

We will foster farmers who feed us on less water and homeowners who sprout native grasses and day lilies instead of turf. We will find a way to buy, lease, trade and share water through interlinked water systems that serve our greater Colorado community with our pooled financial resources.

We will enlarge existing reservoirs, build strategically placed new ones, and employ underground storage.

We will insist on being rate payers of energy utilities that mind a strict water budget and harness the bounty of our strong winds and many sunny days. We will develop equitable water sharing criteria for humans and the environment in our drought plans.

We will put our climate scientists to the task of translating the global, regional, and watershed signs, signals, and trends into predicative tools that lend themselves to prudent risk taking.

And we will welcome many more Coloradans and visitors to this land we love.

Colorado Foundation for Water Education 1580 Logan St., Suite 410 | Denver, Colorado 80203 303-377-4433 | cfwe.org

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Colorado Foundation for Water Education

Rafters (top) navigate the Arkansas River. A crowd gathered in 1947 (bottom) to watch the first water flow from the Adams Tunnel, a key component of the Colorado-Big Thompson Project.