Impacts of irrigation on regional water resources in the coupled climate system

Abstract:

Widespread irrigation alters regional climate through changes to the energy and water budgets of the land surface. Within general circulation models (GCMs), simulation studies have revealed regionally significant changes in temperature, precipitation, and other climate variables. These irrigation impacts are especially notable in key water stressed regions of Asia, western North America, the Mediterranean, and the Middle East. Here we investigate the feedbacks of irrigation with a focus on regional water availability in model simulations. We use two GCM configurations, with and without irrigation, to understand irrigation-induced changes in regional water balances. Importantly, while most other GCM irrigation analyses have focused on monthly changes, we explore changes in daily climate variables. Our simulations reveal shifts in runoff that vary dramatically by region. For example, California’s Central Valley experiences substantial shifts in daily runoff, while runoff is relatively insensitive to irrigation in the Ganges-Brahmaputra basin. It is important to understand such feedbacks, as we face a future with great uncertainty in water-resource availability.