The Colorado River has lost enough water because of climate change since 2000 to supply the Central Arizona Project for a year, researchers for a new federal study found.

In a finding an outside water expert called “eye-popping,” the study concluded that the river loses nearly 10% of its annual flow for every increase in temperature of 1 degree Celsius, or 1.8 degrees Fahrenheit.

The amount of water that didn’t flow down the Colorado due to climate change since 2000 was about 1.5 million acre-feet, or about 2 billion tons, said Christopher Milly, one of the two co-authors.

Besides closely matching the typical annual delivery of CAP water to Tucson, Phoenix and Pinal County, that’s enough to serve all the drinking water Tucson Water’s customers need for more than 15 years.

From 1913 to 2017, the river’s average annual flow dropped about 20%, and about half that decline was due to warmer weather, Milly said.

The river’s water losses will likely continue, if not accelerate, by a range of 14% to 31% over the next 30 years as temperatures keep warming, said the researchers, who are with the U.S. Geological Survey. Their study was published Thursday in the journal Science.