Some California reservoirs shriveled by two-thirds, forcing the state in April to issue mandatory water restrictions for the first time in its history. Two months later, state officials suspended water allocations to farms, idling 840 square miles of fields.
The current drought is part of a larger pattern of warmth and dryness gripping the West and central Plains. Texas, New Mexico, Oklahoma, Kansas and Nebraska suffered severe drought between 2011 and 2013. Drought struck California and Nevada beginning in 2012, and in 2015 it spread into Oregon and Washington. By midsummer, low stream flows and warm water had killed half the annual sockeye salmon breeding run in the Columbia River. Large wildfires fed by dry vegetation scorched the West Coast.
The drought may ease this winter, with warm Pacific El Niño waters expected to trigger heavy precipitation in parts of the West. But it’s likely to be a short reprieve. A study published in February suggests that a megadrought lasting at least 35 years is 60 to 80 percent likely to occur in the Southwest or central Plains after 2050.
Groundwater across the West has been depleted from overuse, shrinking aquifers that cities and farms typically relied on during dry times. Forty cubic miles of water — enough to fill 64 million Olympic swimming pools — have disappeared from beneath California’s Central Valley alone. “We basically no longer have a buffer,” says Gleick.