GPS station in California's Inyo Mountains, cropped photo by Shawn Lawrence, UNAVCO
A lot of harrowing news this week on the extent of the rain and snowfall drought that has seized our part of the world. Scientists at the Scripps Institution of Oceanography released findings today showing that so much water vanishing "is causing the entire western U.S. to rise up like an uncoiled spring." The effect was noticed when scientists observed that GPS stations placed across the West for the National Science Foundation’s Plate Boundary Observatory had all moved upward since the drought grew intense and pumping of underground water increased.
A Scripps researcher says "the GPS data can only be explained by rapid uplift of the tectonic plate upon which the western U.S. rests." (He cautions that the uplift has virtually no effect on the San Andreas fault.)
For [Dan] Cayan, a research meteorologist with Scripps and USGS, the results paint a new picture of the dire hydrological state of the west.
“These results quantify the amount of water mass lost in the past few years,” said Cayan. “It also represents a powerful new way to track water resources over a very large landscape. We can home in on the Sierra Nevada mountains and critical California snowpack. These results demonstrate that this technique can be used to study changes in fresh water stocks in other regions around the world, if they have a network of GPS sensors.”
The Scripps team concludes that nearly 240 gigatons of water — that's 62 trillion gallons, most of it groundwater in aquifers — are missing. They say it's "equivalent to a six-inch layer of water spread out over the entire western U.S." This comes the same week that UC Davis researchers said that California has legally allocated five times more surface water than actually exists in good rain and snow years — complicating the painful decisions to be made during droughts like this one about whose water gets cut.
This all comes as we're finding out just how badly farmers and cities have tapped underground water trying to get through the drought. Wells in the Central Valley are dropping. That groundwater is the last resort for much of the state. "If you think the water crisis can't get worse, wait until the aquifers are drained," National Geographic says in a piece this week.
Aquifers provide us freshwater that makes up for surface water lost from drought-depleted lakes, rivers, and reservoirs. We are drawing down these hidden, mostly nonrenewable groundwater supplies at unsustainable rates in the western United States and in several dry regions globally, threatening our future.
Groundwater comes from aquifers—spongelike gravel and sand-filled underground reservoirs—and we see this water only when it flows from springs and wells. In the United States we rely on this hidden—and shrinking—water supply to meet half our needs, and as drought shrinks surface water in lakes, rivers, and reservoirs, we rely on groundwater from aquifers even more. Some shallow aquifers recharge from surface water, but deeper aquifers contain ancient water locked in the earth by changes in geology thousands or millions of years ago. These aquifers typically cannot recharge, and once this "fossil" water is gone, it is gone forever—potentially changing how and where we can live and grow food, among other things.
A severe drought in California—now approaching four years long—has depleted snowpacks, rivers, and lakes, and groundwater use has soared to make up the shortfall. A new report from Stanford University says that nearly 60 percent of the state's water needs are now met by groundwater, up from 40 percent in years when normal amounts of rain and snow fall.
Here's the latest U.S. Drought Monitor map. All that brown covering California denotes "exceptional drought," the highest level of water shortage. You can click the map to see it larger or poke around at the drought monitor website.
Fifty-eight percent of California is considered at the highest drought level.