Quantifying the Irrigation Impact with Groundwater Interaction on Regional Climate in China Based on WRF and RegCM4

As a major anthropogenic activity of changing land use and land cover, irrigation is considered to have a notable impact on the interaction between land and the atmosphere, and further alter the hydroclimate. Due to the rapid expansion of irrigated farmland, the North China Plain (NCP) has already become one of the most intensified agricultural regions in the world. The massive application of irrigation fulfills the explosive agricultural demands, but it also rises public concerns about the potential climate changes that it may bring to the NCP and its surrounding area. The scarce water resources in the NCP not only increase the climate sensitivities to hydrological variations, but also enhance the dependence on groundwater irrigation, which may aggravate the interference on the local climate. This study aims to investigate the regional irrigation impact on the NCP and its surrounding area, especially how precipitation reacts during the irrigated season. We conduct 20-year comparable experiments with and without irrigation using two state-of-art regional climate models (RCMs), WRF and RegCM4. According to our results, the most intensive irrigation happens in late spring or early summer, since precipitation supply is trivial while the water demand is expansive. The induced irrigation water facilitates evaporation and decreases the surface temperature. In May, the surface cooling produces anticyclonic wind differences in the low and midlevel atmosphere, which inhibits convection and stabilizes the atmosphere. However, the cooling stabilization is overwhelmed by the moistening effect over the NCP region. Convective available potential energy (CAPE) escalates greater than convective inhibition (CIN) and the increase in latent heat substantially lifts the total moisture static energy (MSE), which frequently triggers convective rainfall and in turn brings significant increases in the NCP precipitation in May. This study proposes a moistening-dominant irrigation impact in the NCP, which is different from the prevalent cooling-dominant mechanism raised in other regions. Notably, the reliability of our results is considerably improved by concluding the comparison of structurally distinct RCM simulations. Furthermore, we will introduce preliminary results based on RCM simulations incorporating a groundwater module to uncover the interactions between irrigation, groundwater, and the atmosphere over the NCP region. This research was supported by project GRF16309719, which was funded by the Research Grants Council (RGC) of Hong Kong.