Sid Perkins writes for Science News,
SAN FRANCISCO — In the past six years, the irrigation of crops in California’s Central Valley has pulled groundwater from aquifers there at rates that are unsustainable if current trends continue, scientists say.
The Central Valley, which covers about 52,000 square kilometers, is one of the world’s most productive agricultural regions, says Jay Famiglietti, director of the University of California Center for Hydrologic Modeling in Irvine. In 2002, farmers there produced more than 250 different crops worth a total of around $17 billion — an amount that adds up to around one-twelfth of the nation’s agricultural production, he notes.
But the productivity of those fertile fields is increasingly at risk: Satellite data suggest that more than 20 cubic kilometers of groundwater has been pumped from the valley’s aquifers since October 2003, Famiglietti reported December 14 at the fall meeting of the American Geophysical Union. That’s roughly 4 percent the volume of Lake Erie.
Famiglietti and his colleagues analyzed data gathered by the twin satellites of the GRACE mission, which can discern and measure the movements of water both above and below the ground, on a month-to-month basis (SN: 1/4/03, p. 6). Between October 2003 and March 2009, the San Joaquin and Sacramento River basins — the watersheds that include the Central Valley — together lost more than 31 cubic kilometers of water, the data suggest. About one-third of that net loss evaporated from the soil or flowed out to sea after melting from the region’s snowpack or being pulled from surface reservoirs in those watersheds.