The western United States has lost 63 trillion gallons of water over the past 18 months of severe drought, causing the surface of the earth to rise, according to a new study by Scripps Institution of Oceanography in La Jolla and U.S. Geological Survey.
The amount of water lost is the equivalent of flooding the entire West, from the Rockies to the Pacific, with four inches of water, said researcher Duncan Agnew, professor of geophysics at Scripps Institution of Oceanography.
In a normal water year, rain and snow replenish water supplies that naturally evaporate, cycle through plants into the atmosphere and runoff into the ocean. But the gripping drought has taken a toll, said Agnew, and the water depletion is causing the earth to lift — up to a half-inch in some regions, such as the Sierra Nevada.
“You can think of the earth as like a rubber ball, and if you push down on the rubber ball it goes in.” Agnew explained. “And if you stop pushing down it comes out.”
In the same way, if water is added to the earth, it pushes the surface down, he said. When the weight of the water is removed, the crust springs upward.
Agnew, who specializes in studying earthquakes and their impact on shaping the earth’s crust, looked at data from hundreds of GPS monitors that are used primarily for seismic research.
“The secondary goal was to look for other things that would cause the earth to deform and so this is a slightly unexpected benefit of having this network,” Agnew said.
Agnew hopes the data will help guide future water management and legislation.
“Because it will give us a better understanding of what’s actually happening with the water system in California and throughout the west,” Agnew said.
