Since 2004 the Colorado River basin — which provides water for seven states — has lost enough water to fill Lake Mead twice.
That’s the word from a new study by researchers at NASA and the University of California, who used satellite data to do a first-ever quantifiable measure of how much groundwater people in the American west and southwest have used up in the current spate of droughts. According to the Wall Street Journal, the team determined that from 2004 to 2013 the basin lost 17 trillion gallons of water, which is enough to supply 50 million homes for a year. Three-fourths of that loss was groundwater, and the fastest rates of depletion occurred in 2013 — following one of the driest years on record.
The Colorado River basin supplies the water for about 40 million people and four million acres of farmland across California, Arizona, Colorado, New Mexico, Nevada, Utah and Wyoming.
The study employed a pair of satellites launched by the GRACE mission in 2002, and translated their data on the fluctuations in the Earth’s gravitational pull into changes in total water storage. Separate data sets disaggregated factors like snowpack, soil moisture, surface water, and groundwater. One resulting drawback is that the data can’t get especially granular, nor can it tease apart whether water declines resulted from increased pumping or from lower recharge rates in the basin itself — though the former would go up and the latter would go down during a drought.
The system, described by Jay Famiglietti, one of the study co-authors, as “scales in the sky,” has already been used to measure groundwater depletion in California specifically as well as the Middle East. Just to be sure, the researchers also checked their conclusions against measurements taken from 74 individual wells throughout the surveyed area. The trends in the wells matched the trend in the satellite data.
“That gives us confidence in what GRACE is seeing,” said Stephanie Castle, a researcher at the University of California, Irvine, and the study’s lead author.
“We didn’t think it would be this bad,” Castle continued. “Basin-wide groundwater losses are not well documented. The number was shocking.”
Lake Powell and Lake Mead, both parts of the Colorado River basin, serve as some of the largest reservoirs for that area of the country, and officials are increasingly alarmed by water shortages in both lakes. Between the drought and the demand of rising populations, Lake Mead recently hit its lowest water level ever.
California especially has been punished by droughts in recent years, according to the U.S. Drought Monitor, with every last inch of the state covered by “moderate” or “exceptional” drought in April. More than 80 percent of the state is now in extreme drought, as defined by the U.S. Drought Monitor, and things are anticipated to stay that way at least through October. And work released last week estimated the economic damage from the drought this year at $2.2 billion in losses for the California agricultural industry, along with 17,000 jobs gone.
The New York Times just reported that about 34 percent of the lower 48 states have been in moderate drought (as defined by the Drought Monitor) or worse as of July 22. And while the Drought Monitor data only goes back to 2000, the Palmer Index goes back over a century, revealing the current drought is on par with the epic droughts of the 30s and 50s.
Not surprisingly, residents in the most drought stricken states also tend to be the ones who consume the most water, which often means pulling from groundwater reservoirs. Per capita usage is highest in places like California, Arizona, Nevada and New Mexico, and much of the excess usage goes to watering plants, lawns, and landscapes. As much as half of that water is in turn wasted, as it evaporates or runs off thanks to inefficient irrigation methods.
California is also instituting mandatory water restrictions for the first time. The rules would ban wasteful outdoor watering, hosing down sidewalks and driveways, and will require a shut-off nozzle for hoses. Maximum penalties could reach up to $500, enforceable by any public employee empowered to enforce laws, including local water agencies. Work by the Natural Resources Defense Council has suggested that the right combination of water efficiency and conservation methods could close California’s current gap between its water usage and water supplies with room to spare.
Studies have also linked the droughts to climate change, as warmer temperatures alter weather systems to bring precipitation in wider circles around much of the American west. Climate change also brings precipitation in shorter, bigger bursts, and more heat in turn speeds up evaporation and prevents the accumulation of water resources.