Dramatic decrease in streamflow from the headwater source in the central route of China's water diversion project: Climatic variation or human influence?

The Danjiangkou Reservoir is the headwater source of the central route of China's South to North Water Diversion Project (SNWDP). Average annual streamflow into the Reservoir was 40.97 km 3 from 1951 to 1989, while it was 31.64 km 3 from 1990 to 2006. Between the two periods, the average annual streamflow was reduced by 9.33 km 3 , accounting for 71.8% of the proposed amount of water diversion of the central route (13 km 3 per year). The sharply decreasing streamflow would inevitably have negative impacts on the implementation of the SNWDP. The reasons for the decrease in streamflow should be investigated before developing any adaption strategies. In this study, the impacts of climatic variation and human activities on streamflow were evaluated by a climate elasticity method. The results show that the impact of climatic variation (indicated by precipitation and potential evapotranspiration) was responsible for 84.1–90.1% of the streamflow reduction, while human activities or other indentified uncertainties contributed 9.9–15.9% of the streamflow reduction. The observed 69.89 mm decrease in average annual precipitation contributed 81.6–87.3% of the decrease in streamflow. According to the observed data during the study period, the planned water diversion could lead to an ecological disaster of the downstream area of the Danjiangkou Reservoir in certain years. We suggest that the water diversion from the Danjiangkou Reservoir should be conducted in an adaptive manner to avoid such an adverse consequence, instead of the current plan of a fixed annual amount of water.