Extensive agricultural irrigation can significantly affect local climate and may be masking the effects of global warming in some areas, a new study suggests.
In arid and semiarid regions, irrigation enables farmers to grow crops that wouldn't naturally thrive. But adding large volumes of water to normally dry ground changes the climate in many ways, says Lara M. Kueppers, an ecosystem scientist at the University of California, Merced. For example, irrigation typically darkens the soil, which then absorbs more heat. The resulting increase in evaporation cools the air and boosts humidity, she notes.
Kueppers and her colleagues used computer models to estimate the climatic effects of irrigation in California, where farmers provide extra water to around one-twelfth of the state's land. One set of simulations depicted modern land use, and another set simulated only natural vegetation.
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