Climate modelers at Columbia University report a predicted 10 percent drop in the river's flow in the next few decades may signal water shortages for some 40 million people who depend on the Colorado River Basin for water.
"It may not sound like a phenomenally large amount except the water and the river is already over-allocated," Richard Seager, a climate scientist at Columbia's Lamont-Doherty Earth Observatory, said.
The study's findings suggest the American Southwest is becoming more arid as temperatures rise and rainfall patterns shift from human-caused climate change, and follows a major study of the Colorado River Basin by the U.S. Department of Interior that projected longer and more severe droughts by 2060 and a 9 percent decline in the Colorado's flows.
"The projections are spot on," said Bradley Udall, a University of Colorado, Boulder, expert on hydrology and policy of the American West. "Everyone wondered what the next generation of models would say. Now we have a study that suggests we better take seriously the drying projections ahead."
With alternate water sources all but tapped out, he said, the West will likely have to meet the Colorado River decline by cutting back on water use.
"You can't go build another water project," he said. "That's what makes this problem so difficult."