“California’s Central Valley is an agricultural machine. The valley, which accounts for one-sixth of irrigated lands in the United States, produced crops worth $US 21 billion in 2007, according to the most recent U.S. Census of Agriculture, a comprehensive analysis of U.S. agricultural production.
“Irrigation in the Central Valley also generates an important, less visible export: water vapor. Through evaporation, that water vapor, once aloft, is a significant source of summer precipitation and streamflow hundreds of kilometers away in one of the nation’s most water-scarce river basins, adding enough water each year to the Colorado River to cover the daily needs of 3 million people, according to startling and intriguing climate-modeling research from scientists at the University of California, Irvine, and National Taiwan University.
“The study sheds light on a vital but poorly understood component of the water cycle, providing a first estimate for how irrigation in one region can still affect the water balance of a distant, geographically disconnected river system. According to the study, evaporation from Central Valley irrigation increases the summer flow of the Colorado River by 28 percent — or 400 million cubic meters (325,000 acre-feet) — compared to having no irrigation at all. In the Four Corners region, the effect is even more pronounced, increasing summer flows by 56 percent.”
Read more: Circle of Blue