SCIENCE

World’s Aquifers Losing Replenishment Race, Researchers Say

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Gine Celli climbing out of an irrigation canal that is covered in dried salt on a farm near Stockton, Calif. New studies warn about the depletion rates of aquifers in food-producing regions that support up to two billion people.Rich Pedroncelli/Associated Press 
From the Arabian Peninsula to northern India to California’s Central Valley, nearly a third of the world’s 37 largest aquifers are being drained faster than they are being replenished, according to a recent study led by scientists at the University of California, Irvine. The aquifers are concentrated in food-producing regions that support up to two billion people.
A companion study indicates that the total amount of water in the aquifers, and how long it will last at current depletion rates, is still uncertain. “In most cases, we do not know how much groundwater exists in storage” to cover unsustainable pumping, the study said. Historical estimates, it argues, probably have unrealistically overstated total groundwater volume.
“We’re depleting one third or more of the world’s major aquifers at a pretty rapid clip,” said Jay S. Famiglietti, a professor of earth system science at the University of California, Irvine, and a leading researcher for the two studies. “And there’s not as much water there as we think.”

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Dr. Famiglietti and his colleagues found that eight to 11 of 37 major world aquifers are overstressed, meaning they are losing much more water than man or nature returns to them.
The new studies do not come as a surprise to hydrologists like Jerad Bales, chief scientist for water at the United States Geological Survey. But for him and other experts, an open question is whether the governments and individuals who control groundwater can or will work to gain more knowledge about the extent of the resource and how much use is sustainable.
Another question is whether those with responsibility for managing the aquifers will act to limit groundwater use, particularly if groundwater is essential to their livelihoods.
“We still have a ways to go in terms of learning how, and having the willpower, to manage our groundwater systems,” Dr. Bales said. “We need to think about it more. Water — people all over the world think, ‘If it’s under my property, it’s my resource.’ But it affects everybody.”
Pradeep Aggarwal, who leads the isotope hydrology division of the International Atomic Energy Agency in Vienna, said in an interview that there was growing recognition of the extent of groundwater depletion but that the problem remains “an orphan.”
“Unless the government has an alternative to provide for their livelihoods, who is going to stop it?” Dr. Aggarwal said.
A farmer, he added, will figure that “my livelihood depends on pumping that water — if I stop pumping it, my neighbor keeps pumping it.” The problem of groundwater depletion, he said, cannot be solved by individuals. “This requires action on a larger scale,” Dr. Aggarwal said.
The stress on the most-used groundwater, measured over broad geographies by a NASA satellite that has provided 13 years of data, is a matter of real concern because, as the study said, “groundwater is currently the primary source of freshwater for approximately two billion people.”
Another scientist, Marc Bierkens, who holds a chair in earth surface hydrology at the Department of Physical Geography at Utrecht University in the Netherlands, estimated that about 20 percent of the world’s population depended on crops irrigated by groundwater. In 2012, he published a study in the journal Nature that pointed to the same groundwater overuse reflected in the NASA data.
“Humans are overexploiting groundwater in many large aquifers that are critical to agriculture, especially in Asia and North America,” the Bierkens study said.
Details about individual aquifers are hard to come by. The data from NASA’s twin Gravity Recovery and Climate Experiment (Grace) satellites cannot show a level of detail below 150,000 square kilometers.
Dr. Famiglietti, who is also senior water scientist at NASA’s Jet Propulsion Laboratory, said that for the managers who have some control over the use of aquifers, the data from Grace is “too coarse” to provide useful data for local decisions. “They are waiting for us to do the research — we call it downscaling it to a resolution they can use, that makes it actionable for them,” he said.
The volume of water in 11 of the 37 aquifers studied has declined over more than a decade, according to the study, which was just published in the journal Water Resources Research.
The researchers looked at what appeared to be the loss of groundwater in the aquifers — many of the most stressed are in arid or semiarid regions — and examined how the water has been used, whether for irrigation, supplying the daily needs of large populations or for industrial purposes.
“Quantifying our understanding of how we use water in the world is very important, especially when the resource becomes limited,” Dr. Famiglietti said. “It’s important to understand where the big users are because that is key to affecting management in the future.”