Science News: As farmers irrigate California’s Central Valley, water that evaporates from the fields travels east to Utah, Colorado, New Mexico, and Arizona, where it increases summer rainfall and runoff into the Colorado River, according to a study published in Geophysical Research Letters. An earlier study had noted that watering crops in the Central Valley cools local temperatures and increases humidity. But to see how irrigation affects the climate outside the region, Jay Famiglietti of the University of California, Irvine, and Min-Hui Lo of the National Taiwan University in Taipei designed computer simulations of global climate over a 90-year period and increased water to the Central Valley during the months of May through October. They found that irrigation in California not only sends more water circulating in the atmosphere of the US Southwest but also alters circulation over the entire region, which, in turn, draws in even more water vapor from the Gulf of Mexico. Although the study sheds light on the consequences of people’s use of water and how it can affect climate, many more variables need to be taken into account to gain a more complete understanding of that complex process.