Comparative analysis of evaporation and influencing factors between Three Gorges Reservoir and Taihu Lake

Abstract

[Objective] Canyon-shaped reservoirs exhibit significantly different morphological characteristics compared to lakes or lake-type reservoirs. However, in evaporation studies, knowledge and estimation method derived from lake evaporation are often directly applied, which may lead to substantial biases. By comparing the evaporation characteristics and influencing factors between a typical canyon-shaped reservoir(Three Gorges Reservoir) and a lake(Taihu Lake), the differences are revealed from the perspectives of energy balance and water vapor transport, providing support for improving the understanding and estimation accuracy of evaporation in canyon-shaped reservoirs. [Methods] Based on long-term observational data from the floating evaporation station at Badong in the Three Gorges Reservoir(2014—2021) and the Taihu Lake Platform Mountain station(2014—2018), the energy balance equation was employed to analyze the heat storage changes and water vapor transport characteristics of the two water bodies. The monthly evaporation, heat storage variations, and the relationships between the evaporation diffusion coefficient, horizontal wind speed, and water-air temperature difference were compared to uncover the driving mechanisms of evaporation in the two systems. [Results] The study revealed that:(1) The monthly evaporation of the Three Gorges Reservoir exhibits a unique bimodal pattern with peaks in August and December, with the December peak lagging five months behind the net radiation peak, while Taihu Lake shows a single peak in August with only a one-month lag.(2) The heat storage variation in the Three Gorges Reservoir(-12.1 to 14.4 mm/d) was significantly greater than that in Taihu Lake(-0.97 to 0.97 mm/d), with deep-water heat storage effects leading to distinct seasonal variations in evaporation and water temperature between the two.(3) The evaporation diffusion coefficient in the Three Gorges Reservoir shows weak correlation with horizontal wind speed and no significant dependency, remaining stable under positive water-air temperature differences but increasing during inversion periods. In contrast, Taihu Lake's vapor transfer coefficient was influenced by wind speed and increased with the water-air temperature difference. [Conclusion] The evaporation characteristics of canyon-shaped reservoirs like the Three Gorges Reservoir and their energy and dynamic drivers differ significantly from those of lakes(e.g., Taihu Lake). The impact of water heat transfer on energy balance and valley wind circulation induced by topographic effects are likely the primary causes. Therefore, lake-based evaporation method should not be directly applied to canyon-shaped reservoirs. Instead, specialized approaches tailored to canyon-shaped reservoirs must be developed for evaporation observation and estimation.

Keywords

Three Gorges Reservoir / canyon-shaped reservoir / lake / Taihu Lake / vapor transport / water heat storage / influencing factors / evaporation characteristics