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