Irrigation-induced impacts on near-surface climate under future scenarios

Irrigation plays an essential role in the Earth system by changing water, energy, and carbon fluxes, and then affecting the climate. Many previous studies have been conducted to explore its impacts on near-surface climate, highlighting its cooling effects on air temperature, especially during hot extremes. However, most studies do the exploration during the historical period and only focus on temperature. Projected greenhouse gas emissions and land use datasets have made it possible to extend the investigation under future scenarios, but there are no datasets about predicted irrigation techniques shares information. To address this issue, we create a dataset containing spatial distribution of drip, sprinkler, and flood irrigation techniques, based on a simple assumption that richer and drier countries will invest more in irrigation system upgrades. Then, the Community Earth System Model version 2 (CESM2) is developed to be able to represent different irrigation techniques for one crop type in one gridcell. Finally, with the newly created dataset and modified CESM2, we detect irrigation's impacts on heat and moist-heat stress under SSP1-2.6 and SSP3-7.0. Simulation outputs indicate that irrigation will experience various changes among regions and scenarios. In irrigation hot spots, irrigation will continue to reduce the probability of high-temperature extremes under both scenarios but cannot reverse the warming signal caused by other forcings. Moreover, irrigation's impacts on apparent temperature are very small, and even increase the hours exposed to wet bulb temperature extremes in some regions. This study reveals that irrigation's cooling impacts will persist in the future, but will not be an effective solution to the global warming issue. As for moist-heat stress, irrigation's effects are much more complicated due to its enhancing impacts on air humidity.