New Findings on the Climate Sensitivity of the Water Balance of the Upper Colorado River Basin
Chris Milly1
1 Integrated Modeling and Prediction Division, U.S. Geological Survey
The structure and function of rivers and riparian environments depend on many factors, and these include both climate and human disturbances. Under a changing climate, river restoration efforts may benefit from information about the future trajectory of climate and its impact on water balance. Because of the central role played by the Colorado River for water supply in the Southwest, many scientific investigations have been undertaken over the years in an effort to define the climate sensitivity of runoff in the Upper Colorado River Basin (UCRB). These investigations have yielded frustratingly inconsistent results. We found that the widely varying estimates of sensitivity of UCRB runoff to climate can be reconciled by recognizing certain shortcomings in the methods that have been used until now. By avoiding these shortcomings, we have considerably narrowed the uncertainty in climate sensitivity of the UCRB. Our analysis shows that (and, importantly, explains why) the amount of reduction in flow that results from atmospheric warming is strongly dependent on the seasonal cycle of snow cover; this finding may be useful in predicting which sub-basins within the UCRB are least/most sensitive to warming.