Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation
Evaporating futures
Drought and warming have been shrinking Colorado River flow for many years. Milly and Dunne used a hydrologic model and historical observations to show that this decrease is due mainly to increased evapotranspiration caused by a reduction of albedo from snow loss and the associated rise in the absorption of solar radiation (see the Perspective by Hobbins and Barsugli). This drying will be greater than the projected precipitation increases expected from climate warming, increasing the risk of severe water shortages in an already vulnerable region.
Abstract
The sensitivity of river discharge to climate-system warming is highly uncertain, and the processes that govern river discharge are poorly understood, which impedes climate-change adaptation. A prominent exemplar is the Colorado River, where meteorological drought and warming are shrinking a water resource that supports more than 1 trillion dollars of economic activity per year. A Monte Carlo simulation with a radiation-aware hydrologic model resolves the longstanding, wide disparity in sensitivity estimates and reveals the controlling physical processes. We estimate that annual mean discharge has been decreasing by 9.3% per degree Celsius of warming because of increased evapotranspiration, mainly driven by snow loss and a consequent decrease in reflection of solar radiation. Projected precipitation increases likely will not suffice to fully counter the robust, thermodynamically induced drying. Thus, an increasing risk of severe water shortages is expected.
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Supplementary Material
Summary
Materials and Methods
Supplementary Text
Fig. S1
Tables S1 to S5
Data S1 to S3
Resources
References and Notes
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Science
Volume 367 | Issue 6483
13 March 2020
13 March 2020
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Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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Submission history
Received: 24 August 2019
Accepted: 4 February 2020
Published in print: 13 March 2020
Acknowledgments
This study was facilitated by the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration and by several data providers cited in the supplementary materials. The authors gratefully acknowledge colleague reviews by R. Koster and T. Delworth. Funding: The authors are supported by the U.S. Geological Survey. Author contributions: P.C.D.M. was responsible for the conceptualization and overall direction of the work and wrote the original draft. P.C.D.M. and K.A.D. carried out computations. K.A.D. performed data curation and reviewed the original draft. Competing interests: The authors declare no competing interests. Data and materials availability: No original data collection was performed. The results of this study are reproducible and extensible by use of the cited data sources and other information in the supplementary materials.
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