Shifts in the ground may provide scientists with a new way to monitor areas of drought, a study suggests.
It’s relatively easy to measure precipitation and surface water. But aquifers and other underground sources of water are harder to measure because they’re harder to get to. By placing GPS devices under the earth’s surface and measuring how they move, scientists have been able to estimate exactly how depleted the water in California is, according to a study published in Science today.
The Earth’s crust lifts slightly in a drought, since there’s less water weight pressing it down (geologists call this “uplift”). In the southern Sierra Nevada and the Coastal Range, that uplift is 1 to 3 millimeters a year, a previous study found. Today’s study looked at 11 years of daily uplift data in the western U.S.
The loss over the last 11 years is about 240 gigatons of water, as of March 2014—the equivalent of the annual mass loss from the Greenland ice sheet. California residents have resorted to painting their lawns green to save water. And the state’s agricultural sector, including a booming marijuana business, has been tough on the water supply—to say nothing of how fast the water is being consumed by regular citizens.
There’s some good news when it comes to earthquake risk, though. Some experts have expressed concern that drought could create more stress on the San Andreas fault that runs through California; but today’s study found that stress changes from the water were “unlikely to affect” earthquake risk.
The approach used in today’s study may allow scientists a better way to monitor water conditions underground, the scientists wrote. The GPS stations throughout the western US give a precise view of how much water is in the soil; using the method more widely could dramatically expand the reach of water monitoring, if widely adopted, the scientists wrote. And nowadays monitoring water, they say, “has obvious social and economic benefits.”