Driven by Groundwater Depletion, Colorado River Basin Has Lost Equivalent of Underground Lake Mead

The authors of a new study on water loss in the Colorado River Basin say "large-scale industrial farming" is closely tied to a major depletion of groundwater in the Southwest, where the pumping of groundwater is largely unregulated.

Researchers at Arizona State University used satellite data to measure groundwater supplies across the basin, which runs through seven states including Arizona, California, and Utah.

Measuring the Earth's gravity field to estimate the mass of underground water in the region, they found that the area has lost 27.8 million acre-feet of groundwater since 2003—roughly the same volume as the capacity of the nation's largest reservoir, Lake Mead.

The loss of groundwater has especially accelerated in the past decade, and the basin lost more than twice as much groundwater since 2003 as the amount of water taken out of reservoirs.

"Groundwater is disappearing 2.4 times faster than the surface water," Jay Famiglietti, the senior author of the study and a hydrologist at Arizona State University, told The Guardian.

Groundwater pumping is unregulated in much of the region, and the researchers noted that parts of the basin that have experienced the greatest losses are in areas with industrial alfalfa farming operations.

"Groundwater is disappearing 2.4 times faster than the surface water."

"Overpumping" is the main driver of groundwater loss in the past two decades, Famigletti said. "There's nothing illegal about it, it's just unprotected."

The Colorado River provides water to about 40 million people and millions of acres of farmland.

"Everyone in the U.S. should be worried about it, because we grow a lot of food in the Colorado River Basin, and that's food that's used all over the entire country," Famigletti told The Guardian.

While groundwater has been depleted, hotter temperatures fueled by the burning of fossil fuels have also contributed to especially arid conditions in the region over the past two decades. Since the beginning of the century the Colorado River's natural flow has been 13% lower than it was in the middle of the 20th century.

"We need to recognize where all this is happening and work with the state to put the brakes on," Famigletti told The Washington Post. "We used to say the Colorado River is the lifeblood of the western United States, but now it's becoming groundwater is the lifeblood."

States in the region were forced to reach a federal agreement in 2023 to limit water usage and try to protect the river's supply.

The more water that is lost from the river, Famigletti told the Post, "the more pressure there's going to be on the groundwater" in the basin.

"And then," he said, "it becomes a ticking time bomb."