A new study by NASA and UC Irvine scientists finds more than 75 percent of the water loss in the drought-stricken Colorado River Basin since late 2004 came from underground resources, meaning our parched state and region is even worse off than previously feared.
Jay Famiglietti, a senior writer of the study, explained it this way to me recently as he was packing up his office in UCI's Earth system science wing for the Jet Propulsion Laboratory (JPL) in Pasadena, where he is now researching water while on leave from the university.
When we think of water resources in California, we look at the snow in the mountains that will eventually melt and flow through streams or rivers and places like Lake Mead or Lake Powell. We all "visualize it like a bathtub ring and notice the level of water is up or down," Famiglietti said. "But that's not where most of the water is. Most of the water is groundwater, and groundwater is un-managed. It's the Wild West."
Water above ground in the basin's rivers and lakes is managed by the U.S. Bureau of Reclamation, and its losses are documented. The same cannot be said of water pumped from underground aquifers, which are regulated by individual states.
Quantifying the problem underground sent researchers into space. Well, not literally. Using satellite images from NASA's Gravity Recovery and Climate Experiment (GRACE), Famiglietti and his fellow researchers zeroed in on the Colorado River Basin and determined changes in water mass above and below the surface.
Monthly measurements from December 2004 to November 2013 reveal the basin lost nearly 53 million acre feet (65 cubic kilometers) of freshwater, according to the study. That's almost double the volume of Lake Mead, the nation's largest reservoir. More than three-quarters of the total–about 41 million acre feet (50 cubic kilometers)–was from groundwater, researchers found.
"We don't know exactly how much groundwater we have left, so we don't know when we're going to run out," says Stephanie Castle, a UCI water resources specialist and the study's lead author, in a joint UCI/JPL statement. "This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking."
The Colorado River is the only major river in the southwest part of the U.S. and its basin supplies water to about 40 million people in seven states. The new study has been accepted for publication in the journal Geophysical Research Letters, which posted the manuscript online July 24.