Quantifying the Impact of Cascade Reservoirs on Streamflow, Drought, and Flood in the Jinsha River Basin

Abstract

The Jinsha River Basin (JRB) is the largest hydropower base in China, serving as the main source of the Western Route of China’s South-to-North Water Diversion Project. Under the influence of the reservoirs operation and climate change, the general hydrological regime in the JRB has been altered. Although the change process can be determined through a runoff time-series analysis and hydrological simulation, the individual impacts of the reservoirs have not been quantified. This study aimed to clarify the impact of the reservoirs in the JRB on the runoff, flood, and drought processes using a framework coupling long short-term memory (LSTM) and flood drought assessment techniques. The results are as follows: (1) From 1998 to 2020, reservoirs in the JRB changed the average daily runoff at Pingshan Station by −5.64%, +10.95%, and −10.93% at the annual and seasonal (dry and rainy) scales, respectively. (2) The operation of dams reduces the risk of flood disasters effectively. Compared with the natural river flow, the flood frequency decreased by 7.69%, and the total flow over the threshold was reduced by 37.86%. (3) The operation of dams has changed the duration and severity of drought, reducing extreme drought and increasing moderate and severe drought. In conclusion, the reservoirs in the JRB have positive effects on water resource regulation, and their mitigation of floods and extreme drought provides security for the middle and lower reaches of the Yangtze River. This study provides a reference for the LSTM modeling of reservoir basins, quantifying the impact of reservoirs on runoff, flood, and drought in the JRB.