Feb 20, 2020

Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation

by
P. C. D. Milly, K. A. Dunne
,
Science

The study strongly supports recently published research that says half of the flow loss in the Colorado River during the ongoing drought since 2000 has been due to higher temperatures. The results strongly suggest that future Colorado River flows will trend strongly downward as temperatures warm in the 21st century, potentially catastrophically. These findings apply to almost every area that is dependent on snowpack, which is basically the entire West.

Brad Udall, senior water and climate research scientist at Colorado State University, commenting on the study


  • States that the sensitivity of river discharge to climate-system warming is highly uncertain and governing processes are poorly understood, impeding climate-change adaptation
  • States that meteorological drought and warming in the Colorado River have been shrinking water resources that support more than USD 1 trillion per year of economic activity
  • Resolves the longstanding, wide disparity in sensitivity estimates and reveals the controlling physical processes
  • Examines recorded measurements from 1913-2017 and finds the average temperature across the Upper Colorado River Basin increased by 1.4 C (2.5 F) and the river’s flow decreased by about 20%
  • In previous studies, estimates of potential future declines in the river’s flow — leaving aside any variations in precipitation — ranged from 2% to 15% for each 1 degree C of warming.
  • Estimates that annual-mean discharge in the Colorado River has been decreasing by 9.3% per °C of warming due to increased evapotranspiration, mainly driven by snow loss and consequent decrease of reflection of solar radiation
  • Estimates that warmer temperatures were behind about half of the 16% decline in the river’s flow during the stretch of drought years from 2000-2017 
  • Concludes that projected precipitation increases likely will not suffice to counter fully the robust, thermodynamically induced drying. Increasing risk of severe water shortages is expected