Intense agricultural irrigation induced contrasting precipitation changes in Saudi Arabia

Groundwater extraction has grown tremendously in Saudi Arabia to meet the irrigation water demand since the 1980s, and irrigation is one of the major anthropogenic factors modulating regional hydroclimate. However, the link between irrigation and hydroclimate is not well understood in a dry region such as Saudi Arabia. In this study, we utilize three different regional climate models to explore the physical mechanisms behind the irrigation impacts in this region. The results are robust across models and show that when irrigation is applied, wetter soil results in higher evapotranspiration and cools the lower atmosphere, leading to an anomalous pressure field and alters vapor transportation. Precipitation decreases locally because of the local cooling effect, whereas additional water vapor convergence enhances precipitation west to the irrigated region. This west-east contrast of precipitation change indicates a possible link between irrigation expansion in the 1980s and subsequent decadal precipitation variations in central Saudi Arabia. We further find from observations a decadal west-east contrast of precipitation changes in Saudi Arabia to support the similar finding in the models. This study implies the importance of including anthropogenic water management in climate models and provides a better understanding of how irrigation impacts local-to-regional climate.