Climate change impacts on Yangtze River discharge at the Three Gorges Dam

The Yangtze River basin is home to more than 400 million people and contributes to nearly half of China's food production. Therefore, planning for climate change impacts on water resource discharges is essential. We used a physically based distributed hydrological model, Shetran, to simulate discharge in the Yangtze River just below the Three Gorges Dam at Yichang (1 007 200 km(2)), obtaining an excellent match between simulated and measured daily discharge, with Nash-Sutcliffe efficiencies of 0.95 for the calibration period (1996-2000) and 0.92 for the validation period (2001-2005). We then used a simple monthly delta change approach for 78 climate model projections (35 different general circulation models -GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to examine the effect of climate change on river discharge for 2041-2070 for Representative Concentration Pathway 8.5. Projected changes to the basin's annual precipitation varied between -3.6 and +14.8% but increases in temperature and consequently evapotranspiration (calculated using the Thorn-thwaite equation) were projected by all CMIP5 models, resulting in projected changes in the basin's annual discharge from -29.8 to +16.0 %. These large differences were mainly due to the predicted expansion of the summer monsoon north and west into the Yangtze Basin in some CMIP5 models, e.g. CanESM2, but not in others, e.g. CSIRO-Mk3-6-0. This was despite both models being able to simulate current climate well. Until projections of the strength and location of the monsoon under a future climate improve, large uncertainties in the direction and magnitude of future change in discharge for the Yangtze will remain.