Simulation of Climate effect of large-scale Irrigation in Haihe River Basin

To ensure food security, the annual irrigation water volume in the Haihe River Basin is over 20 billion m³, and large-scale irrigation has a significant impact on the regional climate. In this study, a new irrigation scheme was developed in the land surface module of Weather Research and Forecasting (WRF) model to simulate and analyze the climatic effects of large-scale irrigation in Haihe River Basin. The results showed that irrigation increased the latent heat flux and decreased the sensible heat flux in the Haihe River Basin, with the largest variation in the irrigation period from April to June. Irrigation led to a decrease in temperature in the basin from March to November, with a maximum temperature drop from April to June. The overall spatial performance was that the area with more irrigation had a greater temperature drop caused by irrigation. During the irrigation period, the average temperature drop caused by irrigation in the plain area was 0.64 ℃, with a temperature drop of over 1.0 ℃ in the Shijiazhuang plain area. Irrigation played a leading role in the impact of convective precipitation, leading to an increase of 6.07mm in annual precipitation in Haihe River Basin, mainly concentrated from May to June, and spatially mainly in the Daqing River Basin and the Ziya River Basin, with an increase of 15-30 mm in precipitation during the irrigation period in the Ziya River Mountain area. Irrigation changed near-surface meteorological factors, and reduced the reference crop evapotranspiration in the basin, resulting in a decrease in crop water demand per unit area. Therefore, the climate effect of large-scale irrigation supports and ensures water security in the basin on both supply and demand sides, and to some extent alleviates the contradiction between supply and demand of water resources in the basin.