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Water securityAs climate warms, Colorado River flows will keep shrinking

Published 24 February 2017

Warming in the twenty-first century reduced Colorado River flows by at least 0.5 million acre-feet, about the amount of water used by two million people for one year. From 2000 to 2014, the river’s flows declined to only 81 percent of the twentieth-century average, a reduction of about 2.9 million acre-feet of water per year. One acre-foot of water will serve a family of four for one year, according to the U.S. Bureau of Reclamation. From one-sixth to one-half of the twenty-first-century reduction in flow can be attributed to the higher temperatures since 2000. As temperature continues to increase with climate change, Colorado River flows will continue to decline.

Warming in the twenty-first century reduced Colorado River flows by at least 0.5 million acre-feet, about the amount of water used by two million people for one year, according to new research from the University of Arizona and Colorado State University.

The research is the first to quantify the different effects of temperature and precipitation on recent Colorado River flow, said authors Bradley Udall of CSU and Jonathan Overpeck of the UA.  

This paper is the first to show the large role that warming temperatures are playing in reducing the flows of the Colorado River,” said Overpeck, UA Regents’ Professor of Geosciences and of Hydrology and Atmospheric Sciences and director of the UA Institute of the Environment.

From 2000 to 2014, the river’s flows declined to only 81 percent of the twentieth-century average, a reduction of about 2.9 million acre-feet of water per year. One acre-foot of water will serve a family of four for one year, according to the U.S. Bureau of Reclamation.

From one-sixth to one-half of the twenty-first-century reduction in flow can be attributed to the higher temperatures since 2000, Udall and Overpeck report. Their analysis shows as temperature continues to increase with climate change, Colorado River flows will continue to decline.

Arizona notes that current climate change models indicate temperatures will increase as long as humans continue to emit greenhouse gases into the atmosphere, but the projections of future precipitation are far less certain.

Supplier to seven states
Forty million people rely on the Colorado River for water, according to the U.S. Bureau of Reclamation. The river supplies water to seven U.S. Western states plus the Mexican states of Sonora and Baja California.  

Udall, a senior water and climate scientist/scholar at CSU’s Colorado Water Institute, said, “The future of Colorado River is far less rosy than other recent assessments have portrayed. A clear message to water managers is that they need to plan for significantly lower river flows.”

The study’s findings, he said, “provide a sobering look at future Colorado River flows.”

The Colorado River Basin has been in a drought since 2000. Previous research has shown the region’s risk of a megadrought — one lasting more than 20 years — rises as temperatures increase.