And they’ve already begun, according to The 21st century Colorado River hot drought and implications for the future [open access]. a new report from Scientists at the Colorado Water Institute and the university of Arizona, just published in Water Resources Research.
From the American Geophysical Union:
Warming in the 21st century reduced Colorado River flows by at least 0.5 million acre-feet, about the amount of water used by 2 million people for one year, according to new research.
The research is the first to quantify the different effects of temperature and precipitation on recent Colorado River flow, said authors Bradley Udall of Colorado State University and Jonathan Overpeck of the University of Arizona.
“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. The new paper has been accepted for publication in Water Resources Research, a journal of the American Geophysical Union.
From 2000-2014, the river’s flows declined to only 81 percent of the 20th-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 21st-century reduction in flow can be attributed to the higher temperatures since 2000, report Udall and Overpeck. Their analysis shows as temperature continues to increase with climate change, Colorado River flows will continue to decline.
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.
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.