Irrigation-induced land water depletion aggravated by climate change

Agricultural irrigation withdraws water from multiple resources, possibly causing water scarcity issues. Previous studies predominantly relied on observations or land-only simulations, and therefore generally ignored land-atmosphere interactions, or failed to separate the effects of irrigation from other forcings. Here we analyse the effects of historical irrigation expansion on water fluxes and resources using seven Earth system models. Results show that irrigation expansion substantially increases local evapotranspiration and this extra water out-flux is not compensated by changes in local precipitation. Rapidly expanding irrigation therefore reduces the net water influx from the atmosphere to land (-0.61, -0.21, -0.06, -0.16 mmyr ^-2 in South Asia, the Mediterranean, Central North America, and West Central Asia, respectively). Moreover, other forcings, like climate change, also contribute to the decrease in some regions, further aggravating local water loss. Consequently, regional terrestrial water storage depletion is pronounced in most irrigation hot-spot regions (~500 mm from 1901 to 2014 over South Asia and Central North America, and 100-200 mm in the Mediterranean and Central North America). Our results attribute the land water loss to irrigation expansion and climate change, calling for immediate solutions to tackle the negative trends.