Calif. irrigation creates climate effect

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IRVINE, Calif., Jan. 28 (UPI) -- Irrigation in California's Central Valley doubles the amount of water vapor in the atmosphere, increasing rainfall across the U.S. Southwest, researchers say.

Scientists at the University of California, Irving, report when moisture on the vast farm fields evaporates, the vapor is blown over the Sierra Nevada mountains and dumps 15 percent more than average summer rain in numerous other states.

While the additional water falling on adjacent states can be beneficial, they said, it can also increase the strength of storms and other potentially destructive seasonal weather events.

"If we stop irrigating in the Valley, we'll see a decrease in stream flow in the Colorado River basin," which provides water for about 35 million people and the cities of Los Angeles, Las Vegas and Phoenix, climate hydrologist Jay Famiglietti said.

But the extra water vapor also accelerates normal atmospheric circulation, "firing up" the annual storm cycle and drawing in more water vapor from the Gulf of Mexico, the researchers wrote in the journal Geophysical Research Letters.

When the additional amounts of moisture are fed into developing storms, Famiglietti said, "it's like throwing fuel on a fire."

Understanding irrigation's impact on changing climate and water availability could improve emergency planning in parched or flooded areas, the researchers said.