Asian irrigation accounts for about three-quarters of global irrigation water withdrawal. This irrigation plays an important role in reshaping terrestrial water resources. From an Earth-system perspective, irrigation can also be considered an important anthropogenic forcing on climate. However, previous research focused mostly on local or regional impacts of irrigation on hydrological or climatic systems, while the remote effects that may be caused through atmospheric connections are ignored. Here we estimate that large-scale irrigation in Asia could significantly increase the precipitation and runoff in the Sahel region of Africa by 8% and 12%, respectively. Summertime irrigation in Asia causes a large-scale cooling and induces air sinking. The sinking in Asia then causes the air over Europe and northern Africa to move east, and thus a low pressure anomaly forms over Europe and northern Africa. This creates a cyclonic anomaly that transports vapor from the Atlantic Ocean to the Sahel in Africa. As a consequence, water-vapor flux converges in the Sahel, and precipitation and runoff then increase. Moreover, the irrigation-induced water-vapor convergence releases latent heat and expands the ITCZ northward with a magnitude that rivals the impacts of CO2 emissions. Our results demonstrate that irrigation deserves more attention when studying water resources and climate change in some key regions.
GFDL Lunchtime Seminar
Wed, Mar 20, 2019, 12:00 pm to 1:00 pm
Smagorinsky Seminar Room 209