Climate change impacts on regional agricultural irrigation water use in semi-arid environments

Agricultural irrigation water is essential for global food production. Climate change may significantly increase future atmosphere evaporative demand, which can further intensify local water stress, particularly in arid and semi-arid regions. In this study, we investigate climate change impacts on future irrigation water use (IWU) change, with a focus on a semi-arid (Zhangye) region in Northwest China. Specifically, this approach estimates crop water demand using Penman-Monteith-CO2 equation which is modified to account for atmospheric CO2 concentration impacts. The IWU is then calculated as the difference between crop water demand and effective precipitation. This approach is validated using observed IWU. Combined with climate projections from eight Earth System Models (ESMs), future (up to 2100) IWU changes under different CO2 emission scenarios are evaluated. Results demonstrate that our Penman-Monteith-CO2 approach is robust in IWU estimation, with a relative error of 2.4% during the validation period of 2015–2020. In the medium emission scenario (SSP245), IWU has a significant increasing trend of 1.4×105 m3/yr during 2021–2100, which is mainly attributed to the increased future atmospheric evaporation demand. Interestingly, IWU presents a decreasing trend of − 1.3×105 m3/yr for the high emission scenario (SSP585). This is because strongly elevated CO2 concentration levels can substantially increase crop water use efficiency – leading to reduced IWU, and this impact outweighs the increased atmospheric evaporation demand in the SSP585 scenario. Therefore, our study suggests that future IWU change is determined by both climate change and crop responses to atmospheric CO2 concentration. Finally, we highlight that adjusting crop patterns can reduce both the IWU mean and variation changes, which can potentially alleviate local water stress.