The response of coastal stratocumulus clouds to agricultural irrigation in California

Abstract

Stratocumulus clouds (SC) often exist over the eastern subtropical oceans during the summer and have significant impacts on the surface radiation budget. Both atmospheric subsidence and lower troposphere stability (LTS) have been found to play important roles in maintaining SC. Using global climate model simulations, we find that irrigation in California's Central Valley results in a decrease of land surface temperature, leading to a smaller land-sea heat contrast, and a corresponding reduction in sea breeze, subsidence, and LTS over the near-coastal region. The decrease in LTS directly drives a reduction in modeled SC coverage, and it would arguably do so in reality because of the well-known link between LTS and SC coverage. Consequently, simulated absorbed surface solar radiation over this region increases by 8 W/m 2 (3.7%) due to the reduction in SC cover, resulting in the warming at the Earth's surface. This study has important implications for how SC can change with regard to future climate. In contrast to the general effects of climate change on the formation of SC, our results suggest that irrigation practices in the Central Valley may drive a decrease in nearby SC coverage. Key Points Irrigation causes land temperature decrease and smaller land-sea heat contrast. Absorbed surface solar radiation nearby California increased by 7.8 W/m2. It suggests that SC occurrences may decrease due to California irrigation. © 2013. American Geophysical Union. All Rights Reserved.