Effects of interbasin water transfer on regional climate: A case study of the Middle Route of the South‐to‐North Water Transfer Project in China

Abstract

In this study, a water transfer mechanism was implemented into the regional climate model, RegCM3, to represent water to be transferred by increasing the precipitation that reached the surface in intake areas. The effects of interbasin water transfer on local and regional climates were then studied based on numerical simulations conducted using the RegCM3 model. The Middle Route of the South‐to‐North Water Transfer Project (MRSNWTP) in China was chosen as a case study to investigate the climatic responses under three different water transfer schemes with three intensities. Four 10‐year simulations were conducted, a control run (MCTL) without water transfer, and three water transfer runs (MWT1, MWT2, and MWT3) related to the three schemes. In the three water transfer runs, spatial and temporal water transfer data were derived from the schemes under the assumption that the quantity of water to be transferred into a county in the intake area in a year for each scheme was distributed evenly into each time step. Increases in top‐layer soil moisture and latent heat flux were observed when compared to the control, and these increases were found to occur as a direct result of injecting water into the intake area. The increases in latent heat flux and evaporation were accompanied with decreases in sensible heat flux, mean air temperature, and increases in precipitation in the intake area. These differences were generally small and statistically insignificant, indicating that the water transfer plays a small role in influencing regional climate in our simulations. However, the climatic influence intensity of a water transfer scheme was found to be positively related to the quantity of water to be transferred, and to have strong seasonal variability, with larger effect being observed in spring and autumn than in summer and winter. We also conducted a water transfer run, MWT4, using the same configuration as MWT3 but under the assumption that the quantity of water was distributed evenly into each time step of the first half of the year. Comparison of the two runs shows a stronger seasonal variability in the climatic influence when the water was assigned into the first half of the year than when it was assigned into the entire year. Further analysis revealed that the water transfer could reduce both the seasonal and diurnal temperature ranges at the surface and that the decrease in temperature could diffuse over almost the entire Huabei Plain below 700 hPa, thereby weakening the wind velocity of the easterly breeze. It follows from the analyses of the vertical profiles of the water vapor content and the atmospheric moisture budgets that the water transfer can affect the local and regional climates by changing the local water vapor content and the regional water vapor transports, which in turn influences precipitation.