Satellites track drought-driven groundwater depletion in the West
Matt York, AP
SALT LAKE CITY — The unrelenting grip of drought on the West is depleting groundwater at a pace that some say underscores the need for better documentation and more coordinated management of the resource before it dries up.
A new study led by NASA and the University of California at Irvine tapped into data compiled by the space agency's Gravity Recovery and Climate Experiment, or GRACE, satellite mission.
What GRACE showed is that from December 2004 to November 2013, the Colorado River Basin — which includes Utah and six other states — lost water that is nearly double the volume of Lake Mead, the nation's largest reservoir.
Of that 53 million acre-feet of water that went away, 43 million acre-feet — or more than 75 percent — was groundwater, according to the study.
"This nine-year study shows that groundwater is in decline, and we were not surprised to see that result," said Stephanie Castle, the study's lead author and a water resources specialist at UC Irvine. "(But) this is a lot of water to lose. We thought the picture could be pretty bad, but this was shocking."
The data was derived from tracking the behavior of dual satellites as they passed over the region and influences posed by the varying changes in mass, which would impact the gravitational pull on the satellites.
Water, like mountains or other solid objects, has its own properties of mass, which impacts gravity. The study was accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
"There's only one way to put together a very large-area study like this, and that is with satellites," said Jay Famiglietti, a senior water cycle scientist with NASA's Jet Propulsion Laboratory in Pasadena, California.
The study's revelation about groundwater depletion in the region is another telling component of what hydrologists have said is the driest 14-year-period in the past 100 years for the basin.
"The Colorado River basin is the water lifeline of the 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."
Utah has had its own problems with groundwater depletions in the Beryl-Enterprise area and Enoch, and concerns over extensive groundwater pumping in the Snake Valley led to massive opposition to a Nevada pipeline proposal.
Alan Matheson, senior environmental adviser to Utah Gov. Gary Herbert, said Utah basin depletions led to the state engineer to place a moratorium on any additional withdrawals because the aquifers are not at "safe yield," meaning depletion has eclipsed how fast the aquifers can refill.
"We need to recognize that our water supplies — both groundwater and surface water — are precious in a desert, and we need to make sure that we are managing those resources wisely," Matheson added.
Cory Angeroth, a hydrologist with the U.S. Geological Survey's Utah Water Science Center, said the state has an extensive monitoring network that measures groundwater levels that goes beyond most of its Western neighbors.
"It's really rare for states in the West to have such a broad groundwater data collection network like we have here in Utah, " he said.
The USGS, in fact, has been working cooperatively with the state Department of Natural Resources for 50 years, gathering the data on groundwater resources to be compiled in an annual report that can help guide policy decisions.
"The state engineer has a tough job," said David Susong, another hydrologist with the USGS in Salt Lake City. "It is tough to balance continual growth and development and yet do that also looking at the long-term sustainability and guaranteeing that water is going to be available for people decades and centuries ahead."
Susong said the study shows the predictable effects of years of drought — that people will turn to groundwater to fill the gap.
"If you go through a drought period, your groundwater volumes are going to drop," he said. "If we got into a mega-drought that lasted tens or hundreds of years, certainly we would be in very significant trouble. If we have another wet period, it will all reverse and likely fill back up again. "
But Castle said the extent of the groundwater depletion illustrates an imbalance in the water resource system.
"If we were regulating our groundwater the same way we are regulating our reservoirs, I don't think we would see this kind of signal," she said, adding that the Bureau of Reclamation manages those resources, while groundwater management is in state hands and the level of management and documentation of the resource varies.
"It is risky business."
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