Lake Mead
July 25, 2014

Dry Conditions Causing Massive Underground Water Losses In Colorado River Basin

redOrbit Staff & Wire Reports - Your Universe Online

NASA and University of California, Irvine researchers have determined that over 75 percent of the water lost in the drought-stricken Colorado River Basin over the past decade has come from underground resources – a discovery which suggests that groundwater loss may pose a larger-than-expected threat to the western US water supply.

According to the US space agency, the new study – which has been published online in the journal Geophysical Research Letters - is the first to quantify the degree to which western states rely on groundwater for their water-related needs.

Federal water management personnel report that the Colorado River Basin has been in the midst of a severe and prolonged drought since 2000, and has experienced the driest 14-year period in the last century. Lead author Stephanie Castle, a water resources specialist at UV Irvine, and her colleagues set out to determine what impact that could have on the future water security of the region.

Using data from the NASA Gravity Recovery and Climate Experiment (GRACE) mission to track changes to the basin’s mass (a measure of changes to the amount of water both above and below the surface), the research team discovered that it lost nearly 53 million acre feet of freshwater from December 2004 through November 2013.

That’s nearly twice the amount lost by the largest reservoir in the US (Lake Mead in Nevada), and more than 75 percent of that total, or approximately 41 million acre feet, was groundwater, the research team explained. The basin provides water to roughly 40 million people in seven states, and also helps irrigate some four million acres of farmland.

“We don’t know exactly how much groundwater we have left, so we don’t know when we’re going to run out,” Castle said in a statement Thursday. “This is a lot of water to lose. We thought that the picture could be pretty bad, but this was shocking.”

“There’s only one way to put together a very large-area study like this, and that is with satellites,” added senior author Jay Famiglietti, a senior water cycle scientist at NASA’s Jet Propulsion Laboratory (JPL) and an Earth system science professor currently on leave from UC Irvine. “There’s just not enough information available from well data to put together a consistent, basin-wide picture.”

“The Colorado River Basin is the water lifeline of the western United States,” he continued. “With Lake Mead at its lowest level ever, we wanted to explore whether the basin, like most other regions around the world, was relying on groundwater to make up for the limited surface-water supply. We found a surprisingly high and long-term reliance on groundwater to bridge the gap between supply and demand.”

The rapid groundwater depletion rate will compound the issue, Famiglietti said, because it will further reduce the streamflow of the Colorado River and reduce the supply even more. When combined with population growth and a declining snowpack, he predicts that the long-term ability of the river basin to provide enough water to the residents of the seven US states, as well as Mexico, could be in serious danger.