Rainy years can’t make up for California’s groundwater use

Enlarge / When the California aqueducts can't carry enough water, many areas of the state turn to groundwater. (credit: Steve Proehl)

Over a third of American vegetables are grown in California, largely in the state's Central Valley. The region also produces two-thirds of the nation's fruits and nuts. These crops-and the many Americans who produce and consume them-are heavily reliant on California's water supply. But, given recurrent and severe droughts, the state's groundwater supply has been strained.

When surface water supplies run low, most arid regions worldwide turn instead to their groundwater. But past mismanagement of the groundwater in California has caused parts of the state to sink as much as 30 feet and has also increased the frequency of earthquakes along the San Andreas fault.

Just as importantly, the state's groundwater storage may have been depleted to a point where recovery may take many decades. But, given that this supply is-as its name suggests-in the ground, changes to groundwater aren't the easiest to measure; the available approaches each have advantages and disadvantages. A new study uses a combination of four of the leading methods to show that California's aquifers haven't been recovering from overdrafts during the droughts over the last two decades-and they're unlikely to do so unless policymakers put more limits in place soon.

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