Quantifying the impacts of the Three Gorges Reservoir on water temperature in the middle reach of the Yangtze River

The flow, sediment and temperature regimes of the Yangtze River have changed greatly due to the construction of the Three Gorges Reservoir (TGR). Although past work has focused mainly on the influence of the TGR on water and sediment regimes, less attention has been given to temperature effects. Water temperature changes have important implications for the quality of aquatic habitat and the health of the river ecosystem. This study investigates the impact of the TGR on the water temperature regime along the middle reach of the Yangtze River. To accurately quantify the impact of TGR on water temperature, a regression-modeling framework is employed to reconstruct the temporal pattern of flow and temperature variation along the middle reach of the river in the absence of the TGR. Based on this modeling, reconstructed water temperatures are compared to observed water temperature for the post-impounded period (period 2003-2014) to estimate the influence of impoundment on water temperature. Results show that the influence of the TGR on water temperature alteration exceeds the influence of natural factors. The effect of TGR, relative to unimpounded conditions, is to reduce water temperatures in the spring, summer, and autumn, and to increase water temperatures in the winter. The results of this study illustrate the pronounced effect of the TGR on the temperature regime of the Yangtze River and provide information that can help guide operation of Three Gorges Reservoir to enhance biological conservation.