California's water house of cards

Groundwater supplies at least a third of the state's water. But it's being depleted at a rapid pace, despite efforts to recharge it.

Gov.Jerry Brown's Office of Planning and Research convened a meeting this month of groundwater experts from the University of California to determine what is currently known about the state's underground water reserves and how they may be changing in the future. This and other recent overtures from the office are strong indications of the governor's growing interest in the state's complete water picture.

That picture is increasingly threatened, in particular where groundwater is concerned. California uses more of it than any other state: Nearly 20% of all groundwater withdrawals in the United States occur in California. The importance of this underground water source to the socioeconomic and environmental health of our state cannot be overemphasized.

We rely on groundwater to provide a third or more of our statewide water supply, and even more in drought years. Most of the water pumped is used for irrigation, although an increasingly large amount is being used to support energy production. Unfortunately, the vast reserve that underlies our state is being depleted at a rapid pace.

Our research, using information fromNASAsatellites, shows that since 2002, the Central Valley has been using groundwater at a rate of 800 billion gallons a year. That is roughly equivalent to one full Lake Mead every 12 years. Our findings are consistent with those of theU.S. Geological Survey, which paint a longer-term picture of California's disappearing groundwater.

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