The scientists at the University of California-Santa Cruz found the magnitude of the simulated effect strongly varies with the season, evidenced by large dry-season decreases in monthly mean and maximum temperatures, but little change in rainy-season temperatures.

In their case study of California, which has intense irrigation, Lara Kueppers and colleagues also show irrigation-induced cooling may produce changes in regional air circulation. The researchers hypothesize that past expansion of irrigation may have masked regional warming signals due to greenhouse gas increases since many climate recording stations are in areas with irrigated agriculture. Moreover, they note greenhouse gas emissions and irrigated agricultural area have both increased during the last century.

The research appears in the journal Geophysical Research Letters.