Seven Western states that rely on the Colorado River Basin for valuable water are drawing more heavily from groundwater supplies than previously believed, a new study finds, the latest indication that an historic drought is threatening the region’s future access to water.
In the past nine years, the basin — which covers Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona and California — has lost about 65 cubic kilometers of fresh water, nearly double the volume of the country’s largest reservoir, Lake Mead. That figure surprised the study’s authors, who used data from a NASA weather satellite to investigate groundwater supplies.
About two-thirds of the water lost over the past nine years came from underground water supplies, rather than surface water.
“We were shocked to see how much water was actually depleted underground,” Stephanie Castle, a water specialist at the University of California at Irvine and lead author of the report, said in an interview.
While surface water in the Colorado River Basin is closely regulated by the U.S. Bureau of Reclamation, states are left to regulate groundwater on their own. Some states, like California, have no groundwater management rules; others, like Arizona, have gone so far as to transfer surface water from the Colorado River into underground aquifers for later use.
The Bureau of Reclamation allocates water in strict proportions to each of the seven states within the basin, where 40 million people rely on the Colorado River.