Aquifers are be­ing de­pleted

8 of the world’s largest basins have al­most no re­plen­ish­ment, stud­ies find

Los Angeles Times - - THE STATE - By Rosanna Xia rosanna.xia@latimes.com

More than a third of the largest ground­wa­ter basins in the world are be­ing de­pleted faster than they are get­ting re­plen­ished, and there are lit­tle to no ac­cu­rate data show­ing just how much wa­ter is left in them, ac­cord­ing to two new stud­ies pub­lished Tues­day.

Re­searchers used data from NASA satel­lites to ex­am­ine the 37 largest aquifers in the world. They found that eight were be­ing de­pleted with al­most no nat­u­ral re­plen­ish­ment and five, in­clud­ing the Cen­tral Val­ley, were “ex­tremely” or “highly stressed,” with not enough wa­ter f low­ing back to off­set how much is sucked up. Saudi Ara­bia, In­dia, Pak­istan and north­ern Africa have the most stressed aquifers, ac­cord­ing to the re­search.

The stud­ies spotlight in­creas­ing sus­tain­abil­ity con­cerns as re­gions like Cal­i­for­nia rely more and more on ground­wa­ter dur­ing times of se­vere drought.

“We know we’re tak­ing more than we’re putting back in — how long do we have be­fore we can’t do that any­more?” said Alexan­dra Richey, who con­ducted the stud­ies as a grad­u­ate stu­dent at UC Irvine. “We don’t know, but we keep pump­ing. Which to me is ter­ri­fy­ing.”

Many pre­vi­ous stud­ies of ground­wa­ter stor­age re­lied on sta­tis­ti­cal cal­cu­la­tions and looked mostly at how much wa­ter was be­ing pumped from the ground. These lim­ited es­ti­mates were too un­cer­tain to im­prove ground­wa­ter man­age­ment, re­searchers said. For ex­am­ple, past stor­age es­ti­mates for the North­west Sa­hara Aquifer Sys­tem ranged from 10 to 21,000 years.

“This work clearly demon­strates that it is no longer ad­e­quate to con­tinue cit­ing decades-old … es­ti­mates of to­tal ground­wa­ter stor­age,” ac­cord­ing to the new stud­ies, which were pub­lished in the jour­nal Wa­ter Re­sources Re­search.

Richey’s stud­ies use 11 years of data from NASA satel­lites and in­clude a num­ber of other fac­tors, such as pop­u­la­tion, cli­mate and how peo­ple use wa­ter.

The twin satel­lites — known as Grav­ity Re­cover and Cli­mate Experiment, or GRACE, satel­lites — or­bit the Earth and mea­sure the grav­i­ta­tional pull of wa­ter over time. The dif­fer­ence in mea­sure­ments over time shows how much wa­ter the aquifers are gain­ing or los­ing.

The re­searchers said the world’s ground­wa­ter re­serves are prob­a­bly far smaller than pre­vi­ously thought.

The satel­lite data are just a start, Richey said. Only ex­ten­sive, on-the-ground re­search and drilling can de­ter­mine just how much ground­wa­ter an aquifer might have.

Jay Famigli­etti, se­nior wa­ter sci­en­tist at NASA’s Jet Propul­sion Lab­o­ra­tory and a UC Irvine pro­fes­sor, said that aquifers should be stud­ied and val­ued the same way as pre­cious oil re­serves. “We need to drill for wa­ter the same way that we drill for other re­sources,” said Famigli­etti, who worked on both of the stud­ies.

Do­ing this isn’t easy, re­searchers ac­knowl­edged. Ground­wa­ter basins usu­ally are lo­cated in deep, thick lay­ers be­neath the earth’s sur­face, mak­ing it costly — and chal­leng­ing — to drill down to bedrock to find out just how deep the wa­ter goes. In drier re­gions, the ground­wa­ter could be as deep as 2,000 feet.

“We have the tech­nol­ogy, but we need the re­sources to do this ex­plo­ration,” Richey said.

“We con­tinue to pump in re­gions like the Cen­tral Val­ley with­out know­ing how much wa­ter is in stor­age,” Richey said. “We need more study. We need bet­ter man­age­ment.”

Richey’s re­search team in­cluded co-au­thors from NASA, the Na­tional Cen­ter for At­mo­spheric Re­search, Na­tional Tai­wan Univer­sity and UC Santa Bar­bara.

Bob Cham­ber­lin Los An­ge­les Times

FARM­ERS ARE

drilling new, deeper wells to tap dwin­dling ground­wa­ter near the Cen­tral Val­ley town of Porter­ville.

Justin Sul­li­van Getty Im­ages

WELL WA­TER is pumped from the ground in Tu­lare, Calif. The Cen­tral Val­ley’s aquifer is highly stressed, new stud­ies on the global wa­ter sup­ply re­veal.

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