As droughts have ravaged the western US for over a decade, much of the water loss has come from underground resources in the Colorado River Basin, a new study has found. The water loss may pose a greater threat to the West than previously thought.
The study by NASA and the University of California, Irvine found that more than 75 percent of the water loss in the drought-stricken Colorado River Basin since late 2004 came from underground resources. It is the first time researchers have quantified the amount that groundwater contributes to the water needs of western states, NASA said.
The research team measured the change in water mass monthly from December 2004 to November 2013, using data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellite mission to track changes in the mass of the Colorado River Basin. Changes in water mass are related to changes in water amount on and below the surface.
In the nine-year study, the basin – which covers Wyoming, Utah, Colorado, New Mexico, Nevada, Arizona and California – lost nearly 53 million acre feet (65 cubic kilometers) of freshwater, almost double the volume of the nation's largest reservoir, Nevada's Lake Mead. More than three-quarters of the total – about 41 million acre feet (50 cubic kilometers) – was from groundwater, according to a statement by NASA on the project.
"We don't know exactly how much groundwater we have left, so we don't know when we're going to run out," Stephanie Castle, a water resources specialist at UC Irvine, and the study's lead author, said in the 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 southwestern United States, and the water source is relied upon by 40 million people. The surface water in the basin is regulated by the US Bureau of Reclamation (USBR), but the groundwater is regulated by the individual states. Some states, like California, have no groundwater management rules. Others, like Arizona, have gone so far as to transfer surface water from the Colorado River into underground aquifers for later use, the Washington Post reported.
The USBR, part of the Department of the Interior, allocates water from the basin proportionally among the seven states. A study completed by the agency in 2012 “confirmed what most experts know: there are likely to be significant shortfalls between projected water supplies and demands in the Colorado River Basin in the coming decades,” the USBR said on its website. Since then, the federal government, state governments, local municipalities, and Native American reservations have worked together to augment water supplies, conserve and reuse existing water supplies, and plan for the future of the basin.
"We have made substantial progress addressing Colorado River water management over the past several years," Reclamation Commissioner Michael L. Connor said in a statement. "From the interim guidelines for shortage and surplus in 2007, the 2012 signing of Minute 319 to the treaty with Mexico and the latest WaterSMART funding announcements supporting new projects and studies, we remain focused on wise use and new technologies to address upcoming gaps in supply and demand."
But last week, USBR announced that Lake Mead – the reservoir created by the Hoover Dam – had reached its lowest water level since the lake’s initial filling in the 1930s. Since 2000, the lake has lost 4 trillion gallons of water, according to CBS News. It now sits 130 feet below the high-water mark last reached at the turn of the century, and at 39 percent of total capacity. Scientists have determined that the dry spell since 2000 in the Colorado River Basin is one of the most severe in more than 1,200 years.
"It's time for us to wake up. If this drought continues, we're going to be in a terrible situation within the next 12-24 months," Jay Famiglietti, senior water scientist at NASA Jet Propulsion Laboratory, told the Desert Sun.
Famiglietti is currently on leave from UC Irvine, and is the senior author of NASA’s groundwater depletion study. He noted that the rapid depletion rate will compound the problem of short supply by leading to further declines in streamflow in the Colorado River, according to the statement.
"The Colorado River Basin is the water lifeline of the western United States," Famiglietti said. "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."
At the current rate of water use by the seven states, the Bureau of Reclamation has estimated that by 2017, there will be a 50-50 chance of lower water levels prompting the declaration of a shortage. Starting in 2018, the estimated likelihood of reaching that threshold – and cutbacks in water deliveries – rises to 60 percent, according to the Desert Sun.