Effects of Irrigation on Global Climate

February 2nd 2021
This study investigated the effect of observed irrigation changes over the 20th century. Using a dataset of irrigation volumes and a climate model, the effects of the irrigation changes were simulated. In the early 20th century, irrigation led to cooling in the summer in southern and eastern Asia. Irrigation rapidly expanded in North America, Europe and Asia over the century. Irrigation also led to winter warming over parts of North America and Asia in the latter part of the century. Precipitation increases occur primarily downwind of the major irrigation areas. Irrigation begins to significantly reduce temperature trends during the summer over the Northern Hemisphere mid-latitudes and tropics beginning around 1950. The simulations show that irrigation causes an increase in cloud cover for many regions, but the increases do not directly map to the most highly irrigated areas. Eastern India warmed from a weakened Indian monsoon, driven by a cooler Asian land surface and reduced landā€sea temperature contrast. The cooling due to irrigation in the northwestern portions of the Indian subcontinent is about 3 °C relative to the control runs without irrigation. The globally averaged change in temperature from irrigation is a cooling over land of about 0.1 °C.

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