California’s drought has reached epic proportions. Nearly 60 percent of the state is in exceptional drought—the most severe category—and farmers are depleting groundwater reserves at record rates as wildfires break out north and south.
Now there’s something else to worry about: drought-triggered earthquakes.
If you want to sink a well in California and pump out as much water as you can, there historically hasn’t been a lot to stop you. Unlike other Western states, California has never regulated groundwater withdrawals. As a result, over the last 150 years, Californians have pumped nearly 160 cubic kilometers of groundwater from the Central Valley, the state’s agricultural heartland. That’s enough water to fill Lake Powell, Lake Mead, and all the Colorado River reservoirs downstream—twice, with some left over.
Groundwater withdrawal in the Central Valley was accelerating even before the current drought began in 2011. As much as 20 cubic kilometers of Central Valley groundwater may have been pumped out in just the last three years, according to one estimate. That’s about 12 percent of the last 150 years’ total depletion.
With less water in the aquifer beneath it to hold it up, the soil throughout the Central Valley is sinking. In some places, the land is dropping as much as a foot a year, damaging roads and other infrastructure and exposing communities to increased flood risk.
But the missing water wasn’t just holding up the soil; it may have been holding the earth down as well. A study published earlier this year in the journal Nature suggested that the more water gets pumped out of the ground in the Central Valley, the greater the chance of earthquakes on the nearby San Andreas Fault.
It’s no surprise that groundwater pumping can set off earthquakes. A May 2011 quake in Lorca, Spain, which killed nine people and caused extensive damage to historic buildings, is thought to have been sparked by over drafting of the local aquifer.
It would seem the same physical processes operate in California.
