How the West will feel groundwater shortages

New research shows stressed water supplies, as demand increases.

 

Drought-stricken water users in California’s Central Valley have compensated for shortages by pumping groundwater at a furious rate. In some parts of the valley, the water table has dropped roughly 60 feet in a single year. Researchers say such practices are moving us toward hydrological bankruptcy.

A new worldwide snapshot of the planet’s largest underground aquifers suggests things are even worse than we thought. Researchers at the University of California, Irvine, released two papers on the topic this week in the journal Water Resources Research. Globally, 13 of the 37 largest groundwater reserves, including the Central Valley, are “overstressed” or “extremely stressed,” meaning they’re being consumed much faster than replenished.

Irrigation canal and fields in California's Central Valley
USGS
“It’s much worse than what we thought, or what we think it is even now,” Jay Famiglietti, senior water scientist with NASA’s Jet Propulsion Laboratory and an Irvine professor, said. Famiglietti notoriously declared this spring that California has only “about one year of water left,” based on his analyses.

Groundwater depletion isn’t a new problem for the West, although it’s literally hidden from view. Arizona’s pumping habits once dried up the Santa Cruz River through Tucson and caused subsidence around other cities. Idaho’s Snake River Plain and Colorado’s Denver Basin have suffered decline, thanks to bustling growth and groundwater pumping. The southern half of the High Plains, or Ogallala, Aquifer, covering parts of Colorado, Kansas, Oklahoma and Texas, is dropping so fast it may not be able to support irrigation three decades from now.

Famiglietti and his colleagues used remote-sensing data from NASA satellites to get a detailed understanding of aquifer groundwater levels and recharge rates. The findings challenge past aquifer storage estimates as too large and depletion estimates as too conservative. In other words, to the extent that we’re managing our groundwater systems at all, we are doing so without accurate information. The studies also highlight that many of the largest, overused groundwater basins are critical food-producing areas. Reduced drinking-water supplies and food production could potentially trigger political or social instability.

Map of trends in global groundwater storage
UC Irvine/ NASA
The Middle East’s Arabian Aquifer and the Indus River Basin of India and Pakistan are the world’s two most stressed systems, based on the research. The Central Valley, considered “extremely stressed,” isn’t far behind and has seen sharp declines in recent years. The Ogallala, also included in the studies, rates better than the Central Valley but still show signs of stress.

As in California, many water-stressed areas around the world are exacerbating shortages, as people rely more on groundwater to meet demands. California became the last Western state to enact groundwater-monitoring laws in 2014.

“It’s almost too much for our water managers to have to cope with the lack of available surface water and the declining groundwater,” Famiglietti said, noting that many managers focus on river flows while overlooking connections and impacts to underground aquifers.

Flow shortages and reservoir declines within the Colorado River Basin have resulted in massive regional groundwater losses during the past decade of drought. A 2014 report by Famiglietti and others found that 75 percent of the basin’s water losses since 2004 have come out of underground aquifers.

Famiglietti and other NASA researchers are now taking the satellite data and building a high-resolution computer model to provide better predictions of water availability across the West. That initiative, called Western States Water Mission, should give scientists, managers and policymakers a more complete picture of connections between snowpack, rivers, groundwater and soil moisture, and identify where shortages are occurring.

“The issue comes down to: We don’t include groundwater in our Colorado Basin system of laws and policies,” Famiglietti said. “Groundwater is basically dealt with on a state-by-state level, but we really need to enter into interstate discussions because we’re clearly relying heavily on groundwater to meet allocation demands.”

Joshua Zaffos is an HCN contributing editor. He tweets at @jzaffos.

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