Colorado River Loses 1.5 Billion Tonnes of Water

A vanishing snowpack—courtesy of climate change—is shrinking the Colorado River, and with 40 million Americans and $1 trillion in economic activity in the balance, researchers are urging policy-makers to draft new usage agreements that take a vastly lower flow into account.

A recent report in Science magazine has firmly connected the dots between climate change, lost snowpack, and changes in the Colorado River, writes the Washington Post. The research, conducted by Chris Milly and Krista Dunne, both scientists with the U.S. Geological Survey, found the snowpack feeding the river is “shrinking and melting earlier,” resulting in a reduction of 1.5 billion tonnes of water since 2000. The situation is compounded by the “albedo affect,” in which the loss of reflective snow cover results in even more warming, and more water lost to evaporation.

Drawing on measurements taken from 960 sites throughout the Upper Colorado River Basin—which has seen its average annual temperature increase by 1.4°C since the 1920s—Milly and Dunne “determined that the flow has dipped 9.3% for each temperature rise of 1.0°C.” This puts the river’s average annual flow at “nearly 20% below its historic average,” adds the Post.

The region is projected to warm even further, Milly added, resulting in further reductions in flow. Andrew Mueller, general manager for the Colorado River District, told the Post a further 1.0°C of warming would lead to the evaporation of “nearly five times” the amount of water used by Las Vegas every year.

And yet, as the river dries, the relentless demands of thirsty people and downstream industry are protected by law. “Under a 1922 compact, Upper Basin states—Colorado, Utah, Wyoming, and New Mexico—must deliver an average of 8.25 million acre-feet of water in 10 consecutive years to the Lower Basin states—California, Arizona, and Nevada—and Mexico,” reports the Post. (An acre-foot is roughly equivalent to 325,000 gallons, or 1.23 million litres.) The compact is set to expire in 2026.

While Mueller finds the USGS findings “significantly grim”, report co-author Brad Udall, a senior scientist at Colorado State University, says it could be worse. So far, at least, “we’re looking at a glass that’s 70% full, not half full,” he said.