Satellites show major groundwater loss in California
December 16th, 2009New observations from NASA/German Aerospace Center’s twin Gravity Recovery and Climate Experiment (Grace) satellites reveal that massive amounts of groundwater are being sucked out of California’s Central Valley groundwater aquifers. The unsustainable withdrawals are unreported, unmonitored, and unregulated.
Between October 2003 and March 2009, more than 24 million acre-feet (30 cubic kilometers) of groundwater were pumped out of California’s Central Valley. The withdrawals are more than 4.4 million acre-feet per year, more than three times previous estimates by California’s Department of Water Resources.
Preliminary studies show most of the water loss is coming from the more southerly located San Joaquin basin, which gets less precipitation than the Sacramento River basin farther north. Initial results suggest the Sacramento River basin is losing about 2 cubic kilometers of water a year. Surface water losses account for half of this, while groundwater losses in the northern Central Valley add another 0.6 cubic kilometers annually. The San Joaquin Basin is losing 3.5 cubic kilometers a year. Of this, more than 75 percent is the result of groundwater pumping in the southern Central Valley, primarily to irrigate crops.
Combined, California’s Sacramento and San Joaquin drainage basins have shed more than 30 cubic kilometers of water since late 2003. The overdrafts are leading to declining water tables, water shortages, decreasing crop sizes and continued land subsidence. The findings have major implications for the U.S. economy, as California’s Central Valley is home to one sixth of all U.S. irrigated land, and the state leads the nation in agricultural production and exports.
The California results come just months after a team of hydrologists led by Matt Rodell of NASA’s Goddard Space Flight Center, Greenbelt, Md., found groundwater levels in northwest India have declined by 17.7 cubic kilometers per year over the past decade, a loss due almost entirely to pumping and consumption of groundwater by humans.
The twin Grace satellites monitor tiny month-to-month changes in Earth’s gravity field primarily caused by the movement of water in Earth’s land, ocean, ice and atmosphere reservoirs, thus directly ‘weighing’ changes in water content.