FILE - In this Jan. 3, 2003, file photo, a dry and cracked area near the Lake Mead Marina shows the effects of the lake’s receding water level in Lake Mead, Nev. Drought in the southwestern U.S. is depleting the vast Lake Mead on the Colorado River to levels not seen since Hoover Dam was completed and the reservoir was filled in the 1930s. (AP Photo/The Las Vegas Sun, Aaron Mayes, File)
For more than a decade, photos of the biggest reservoirs on the Colorado River have shown the dramatic drop in water levels caused by prolonged drought. But a study suggests the greatest water losses have gone sight unseen.
Using satellite data to track freshwater losses in the Colorado River Basin from late 2004 to November 2013, researchers estimate that more than 75 percent of the decline was groundwater. The levels of Lake Mead and Lake Powell have gone up and down during that period, but total storage in the two reservoirs is essentially unchanged. Groundwater, on the other hand, was depleted by the equivalent of more than a full Lake Mead.
“We’re so focused on the surface water. But the groundwater is quietly disappearing from the region,” said co-author and University of California, Irvine, Prof. Jay Famiglietti, who is senior water scientist at NASA’s Jet Propulsion Laboratory. “The Colorado River Basin is the water lifeline of the western United States.”
UC Irvine and NASA scientists analyzed nine years of satellite data to measure changes in land mass in the basin, which reflect surface and groundwater supplies. They then compared the groundwater estimates with well data from the U.S. Geological Survey and the Arizona Department of Water Resources. They found that the basin lost nearly 53 million acre-feet of freshwater during the study period, with the bulk of that drop — about 41 million-acre feet — in groundwater. (An acre-foot is enough to supply two households for a year.)
The loss reflects long-term trends in groundwater overdraft as well as stepped-up reliance on wells during a drought that settled over the Colorado River Basin in 2000. “We don’t know how much groundwater there is” in the basin, said the paper’s lead author, Stephanie Castle, a UC Irvine water resources specialist. “Would you continue to use money if you didn’t know how much was in the bank?”
Los Angeles Times