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

Large-scale interbasin water transfer, which changes basins by creating new hydrological cycles, has the potential to affect local and regional climates. In this study, a water transfer mechanism is implemented into the regional climate model RegCM3. It represents water to be transferred as increasing the available quantity of precipitation reached at the surface in intake areas. The effects of interbasin water transfer on local and regional climates are studied based on numerical simulations with the regional climate model RegCM3. The Middle Route of South-to-North Water Transfer Project (MRSNWTP) in China is chosen as a case study to investigate the climatic responses under the three water transfer schemes with the intensities of 7.499, 8.531, and 11.816 billion m3/year (named Scheme 1, Scheme 2, and Scheme 3, respectively) based on the project programming of the MRSNWTP. Four ten-year simulations were conducted, which are the control run (MCTL) without water transfer, and three water transfer runs MWT1, MWT2, and MWT3 related to the Schemes 1, 2, and 3, respectively. In the transfer runs we use the spatial and temporal water transfer data derived from the Schemes under the assumption that the quantity of water to be transferred of a county in the intake area for a year for each of the Schmes is distributed averagely into each time step for the year. The results show that the climatic influence intensity of a water transfer scheme positively relates to its quantity of water to be transferred and has the strong seasonal variability with a bigger effect in spring and autumn than that in summer and winter. Further analysis shows that the water transfer can reduce both the seasonal and diurnal temperature ranges; the temperature decreasing can diffuse over almost the whole Huabei plain below 700 hPa, and hence weaken the wind velocity of the easterly breeze. It follows from the analyses on vertical profile of 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 vapour transports, hence influence the precipitation.