One-third of Earth's groundwater basins could dry up, but scientists don't know when

Californians were recently warned that they have about a year's worth of water left in the state's reservoirs if they are not replenished by rain or snow soon, a scenario that will require tapping even more into underground aquifers than we already have.

Now, the scientist who sounded that clarion call says humans have been depleting roughly a third of groundwater basins around the globe at a rapid rate with little to no water getting reabsorbed, and that we are doing it without knowing how much is in them.

"Available physical and chemical measurements are simply insufficient," said Jay Famiglietti, UC Irvine professor and senior water scientist at NASA’s Jet Propulsion Laboratory, in a statement on Tuesday. "Given how quickly we are consuming the world’s groundwater reserves, we need a coordinated global effort to determine how much is left."

Famiglietti was principal investigator in a pair of studies led by UCI. In one of those studies, researchers found that 13 of the planet's 37 largest aquifers observed from 2003 to 2013 were being depleted without being replenished. 

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Eight of those aquifers were classified as "overstressed." Not surprisingly, they include aquifers in very dry regions where groundwater is the main source of water, such as the Arabian Basin between the peninsula and India, the Murzuq-Djado Basin in Libya, and the Indus Basin between India and Pakistan — areas regularly entrenched in political and economic turmoil.

(A map from UC Irvine and NASA shows the names and locations of the world's 37 largest groundwater basins. Click for a larger view.)

"What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can't supplement declining water supplies fast enough?" said Alexandra Richey, a UCI grad student who is the lead author of both studies. "We're trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods."

Researchers used data from NASA's Gravity and Climate Experiment (GRACE) satellites. By measuring subtle changes in the Earth's gravity, GRACE can indicate shifts in the amount of water in certain segments of the planet, according to researchers.

Five aquifers were classified as "extremely or highly stressed," among them the California Central Valley Aquifer. About 60 percent of California water now comes from groundwater but little water is reentering the soil.

According to a recent report from the Center for Investigative Reporting, all that "deflating" of earth is causing the state to sink in parts.

The second study released Tuesday concluded that, as this rapid depletion of groundwater basins continues unchecked, scientists simply do not have enough information about how much water these natural water reserves contain.

That lack of information makes it difficult to estimate how much longer we can expect the aquifers to provide water, researchers said.

"Estimates of remaining storage might vary from decades to millennia," Richey said in the statement.

In March, Famiglietti minced no words about the severity of the problem when he spoke to Take Two:

Both studies were published Tuesday in the journal Water Resources Research.