Satellites weigh California water
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Nasa satellites have weighed the water lost by the US State of California’s heartland since 2003.
The Sacramento and San Joaquin River Basins which support the highly productive Central Valley have shed over 30 cubic km of water in that time.
The data comes from the Grace mission which detects changes in gravity caused by water as it cycles between the sea, the atmosphere and the land.
It illustrates the impact of a drought but also excessive irrigation use.
“The numbers we’re getting out of this analysis point to groundwater use at unsustainable rates,” said Professor Jay Famiglietti of the University of California, Irvine.
“It’s leading to declining water tables, decreased crop sizes, and continued land subsidence – something that has been going on in the Central Valley for decades.”
Professor Famiglietti has been describing the California situation here at the American Geophysical Union’s (AGU) Fall Meeting, the world’s largest annual gathering of Earth scientists.
It is big issue because of California’s importance to food production in the US.
Its Central Valley is one of the major agricultural regions in the world.
It grows more than 250 different crops, accounting for a little under a tenth of all the food produced in the US by value. But the Central Valley also accounts for about a sixth of all the irrigated land in the US, making the region the second most pumped aquifer in America.
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