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 from the University of Arizona and Colorado State University.
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.
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.
Previous research has shown the region’s risk of a megadrought — one lasting more than 20 years — rises as temperatures increase.
The two researchers wanted to provide water managers with insight into how future projections of temperature and precipitation for the Colorado River Basin would affect the river’s flows.
Udall and Overpeck began by looking at the drought years of 2000-2014.
To see how increased temperatures might contribute to the reductions in the river’s flow that have been observed since 2000, Udall and Overpeck reviewed and synthesized 25 years of research about how climate and climate change have and will affect the region and how temperature and precipitation affect the river’s flows.
Those researchers and others suggest the risk of a multidecadal drought in the Southwest in the 21st century is much higher than climate models indicate and that as temperatures increase, the risk of such a drought increases.
Udall and Overpeck found all current climate models agree that temperatures in the Colorado River Basin will continue rising if the emission of greenhouse gases is not curbed.
"Current planning understates the challenge that climate change poses to the water supplies in the American Southwest," Udall said.