Reconciling Divergent Estimates of the Sensitivity of Colorado River Discharge to Atmospheric Warming

Recent drought and atmospheric warming have heightened concerns about the sustainability of the water resource provided by runoff from the Upper Colorado river basin (UCRB). Despite the major economic importance of this resource and the threat of its diminution by climate change, research has not yet resulted in a consensus on the magnitude of reduction in runoff that can be attributed to warming: recently published estimates span the range from -2% to -15% change in discharge of the river per degree Celsius of warming. We use a monthly water-balance model driven by precipitation and radiation to understand and reconcile past estimates. We explain how the highest estimates are statistical artifacts, while the lowest estimates arise because critical physical processes in the basin are not considered. Our model produces an estimate of -9%/degree for the sensitivity and demonstrates that this value will decline as warming progresses through the 21^st century.