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Rocky Ford Water Year Precipitation Totals

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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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Citizen's Guide to Colorado Climate Change  

This guide presents a range of contemporary climate change information presented by Colorado experts.