Groundwater supplies beneath the world's driest regions -- where water is needed most -- are approaching the point of crisis, warns a commentary piece published yesterday in the scientific journal Nature Climate Change.
Penned by James Famiglietti, a top water scientist at the NASA Jet Propulsion Laboratory in Pasadena, Calif., the commentary includes new satellite data confirming that the amount of water stored in seven of the world's major aquifers -- including California's Central Valley -- declined markedly since the early 2000s.
It is not the first time scientists have raised alarm about global overdependence on groundwater, but Famiglietti said in an interview that little is being done to improve the situation, even as climate change appears set to exacerbate water shortages.
"Those aquifers are in the dry parts of the world -- that's why we rely on them," Famiglietti said. "Because of climate change, those dry areas of the world are getting drier, so there will be less replenishment of an already limited resource."
A chart published with Famiglietti's piece documents a steady decline in California's Central Valley aquifer, the southern portion of the High Plains Aquifer in the U.S. Midwest, the North China Plains aquifer, an aquifer in northwestern India, an aquifer in the northern Middle East, Australia's Canning Basin and the Guarani aquifer in central South America.
Many of these areas are grappling with drought. Northern China is in the midst of its worst drought in 60 years (ClimateWire, Sept. 25). Armed bandits are exploiting dry conditions in northern India, instituting an illegal "water tax" on small villages (Greenwire, July 21).
And in California, farmers and municipalities today are facing unprecedented water cutbacks (Greenwire, Aug. 15). In September, California passed legislation that will, for the first time, manage groundwater on a statewide basis (E&ENews PM, Sept. 16).
GRACE satellites spot depletion
Famiglietti called this move a step in the right direction but said far more needs to be done around the world before the problem is solved.
"It's worse than people realize in part because declining groundwater reserves don't normally get included in assessments of drought," he said.
Famiglietti's concern about groundwater use began with a paper published in Nature in 2009, which used data from NASA's GRACE satellite mission to observe groundwater depletion in India.
The GRACE mission, launched in 2002, consists of two satellites in tandem orbit, each "about the size of a flattened minivan," Famiglietti said.
The GRACE satellites don't take pictures of the Earth's surface. Rather, they measure changes in gravitational pull of the landscape beneath them, dipping down toward the Earth when there's a bigger mass below like a mountain range, and rising up again when there's less mass.
When there's a decrease in mass below due to water depletion, the land actually rises up, allowing the GRACE satellites to measure the change over time. Using ground-based data, other scientists have also measured a rise in land mass over the U.S. West due to water shortages (ClimateWire, Aug. 22).
Famiglietti didn't realize at first that the satellites were documenting such wide-scale groundwater depletion over India. He considers that moment of realization a turning point.
A 'holy crap' moment inspires a broader look
"We spent the first five or so years just figuring out what we are looking at," he said. "Once I realized that what we were looking at in India was groundwater depletion, then when I looked over the rest of the data ... I realized, 'Holy crap, I think this is happening all over the world.'"
This was confirmed in data detailed in later studies, including Famiglietti's commentary published yesterday.
Famiglietti isn't shy about asking policymakers and scientists to try to change course on how groundwater is managed.
"While reversing climate change and its impact on groundwater resources is no longer a possibility for humanity, managing our way through the global groundwater crisis is," he wrote in the commentary.
Famiglietti listed a series of steps he thinks are necessary to address the problem, including acceptance that the gap between water supply and demand can no longer be filled using groundwater, that surface water and groundwater must be managed as a single unit and that agriculture must improve its water use efficiency.
The commentary was a "call to action," Famiglietti said, asking scientists to measure the amount of water in aquifers and report this information across political boundaries. GRACE data are limited in that they measure depletion over very large areas, so he thinks scientists should pursue more exact measurements rather than allowing people to pump from a resource of unknown quantity.
"Just like for oil -- we wouldn't do that with an oil reservoir," he said.
Sandra Postel, Freshwater Fellow of the National Geographic Society and director of the Global Water Policy Project, praised Famiglietti's commentary in an email.
"Groundwater monitoring and management has been sorely neglected in most parts of the world where aquifers serve as crucial sources of supply for irrigated agriculture and cities," Postel wrote. "Without better assessment and management of groundwater, we are flying blind into a future of water stress that will certainly impact food production and food prices, which in turn will unleash civil unrest."
Correction: A previous version of this story included an incorrect title for Sandra Postel.
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