Climate change impacts on Three Gorges Reservoir impoundment and hydropower generation

Climate change is expected to alter regional hydrological regimes, affecting the operation and performance of reservoirs and hydropower facilities. This study examines the impacts of climate change on the performance of the Three Gorges Reservoir (TGR) by means of a detailed daily reservoir regulation and hydropower model, linked to a physically-based hydrological model, and driven by an ensemble of five General Circulation Models (GCMs) under three Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). As precipitation in the basin is expected to increase, the projected mean annual inflow and hydropower generation of the TGR will increase by 3.3-5.6% and 0.9-2.3% in 2040-2065, 7.9%-15.2% and 5.2-8.1% in 2080-2099 respectively. These increases are only statistically significant for 2080-2099 and are seasonally concentrated in the spring before the flood season and the early autumn during the end of the flood season. However, the inter-annual variation of power generation will increase specially in the dry season. The reservoir performance is highly sensitive to the changes in the seasonal distribution and extremes of streamflow. Increases in streamflow that occur in the flood season cause significant increases in the amount of spilled water and advance the time when the reservoir reaches the normal storage level. Additionally, increases in both the inter-annual variation of inflow and the intensity of inflow shortages during extreme drought years in the impounding stage drive decreases in the fully filled rate and average water storage level in the dry season. The utilization rate of water resources under projected extreme streamflow is expected to decrease, reshaping the response of power generation to climate change into a non-linear pattern where increases in streamflow do not proportionally translate to increases in power generation. These findings highlight the complexity of hydropower management and production under future climate change scenarios, motivating the need for introducing detailed regulating models for impact assessment studies and adaptive adjustment of the reservoir management to combat climate change.