By John Upton
California’s Central Valley is one of the world’s most productive crop-growing regions. But growing crops in the vast rich soils requires a lot of water. Some of that water comes from melting Sierra mountain range snow, with a pinch of rainfall mixed into the rivers that are tapped for irrigation. But farmers also pump a lot of their water out of the ground.
Since the early 1960s, about 60 million acre-feet more water has been pumped out of the valley’s aquifers than has seeped back into them. That’s enough water to supply every resident of California for eight years.
Where has that water gone?
A lot of water that is pumped out of the ground evaporates. In some places, that contributes to rising seas, with water being shifted from the land into the oceans.
But in California, scientists have discovered that evaporating Central Valley water turns into clouds that deposit their consignments east of the Sierra, fueling the monsoons of the Southwestern United States and increasing flows in the Colorado River by more than one quarter. The findings were published online Tuesday in Geophysical Research Letters.
California ends up getting some of the water back. Some Colorado River water is diverted and sent west through what the study’s lead researcher, Jay Famiglietti of the University of California at Irvine, dubs an “anthropogenic loop.”
Famiglietti told me that the study illustrates that large-scale water management practices, such as irrigation, can have “profound regional, and even global” impacts.
“We need to understand, much better, what those impacts are,” Famiglietti said.