Long-term dynamics of crop water consumption in the irrigated lands of the Amu Darya basin 

The most water-stressed basins accommodate almost one third of the global irrigated agriculture. Future food production in these basins is threatened not only by excessive water consumption but also by climate change impacts that endanger irrigation water availability and increase water requirements of crops through increasing evapotranspiration (ET). Endorheic river basins in Central Asia are particularly susceptible to climate change. Large-scale irrigation projects during the Soviet period, mainly for water- intensive cotton cultivation, already contributed to the rapid desiccation and salinization of the Aral Sea, formerly the world’s fourth-largest inland water body. Changes in cropping practices after the collapse of the Soviet Union in 1991 included planning less water intensive winter wheat along with an increase in cropping frequency, however the impacts of these changes in land use and of climate change on water consumption remain unknown. Here, we estimated the spatial and temporal dynamics of crop ET and its driving factors across the Amu Darya basin, from 1987 to 2019 using hydrometeorological data, Landsat imagery, yearly maps of cropping practices, and ET estimations derived from the Operational Simplified Surface Energy Balance (SSEBop) model. The results show an overall increase of 20% in crop water consumption despite the decrease in water intensive cropping. Downstream countries Turkmenistan and Uzbekistan have the highest contribution to water consumption. Although changes in cropping practices contributed positively to water demand, annual ET increased in the last 30 years in accordance with the exacerbating temperature rise. Our study provides the first long-term and high-resolution analysis of crop water consumption in the Amu Darya Basin which can support water managers and policy makers towards improved water management decision and planning in a changing climate.