Estimation of Reservoir Evaporation Water Loss in Inland China over the Past 30 Years

Reservoirs have made significant contributions to human access and management of surface water resources, as well as to the production of clean energy, thus playing a vital role in alleviating the water crisis and decarbonizing energy systems through hydropower generation. The rapid growth in reservoir construction has led to an increase in the surface water area, consequently escalating evaporative water losses. As a crucial component of water cycle, most estimation methods for evapotranspiration focus on the land surface, with a relatively rough estimate of the significant evaporation loss from open surface water. Meanwhile, limited by the availability of reservoir geographic information and monthly area series data, there is still a lack of comprehensive and accurate estimation of reservoir evaporation losses. As the country with the largest number of dams in the world, it is necessary to accurately estimate China's surface water evaporation losses associated with its prosperous and developing dam construction. Here, we used the China Reservoir Dataset and LandSAT based Global Surface Water Dataset to reconstruct the monthly area series of 4874 reservoirs in China from 1984 to 2020, and further considering the heat storage of water bodies, the monthly evaporation losses of these reservoirs from 1988 to 2018 were estimated. The results indicate that the average annual evaporation volume of these 4874 reservoirs is 18.55 × 10⁹ m³, equivalent to 31% of the total domestic water consumption of China (in 2021). During the research period, the evaporation rate shows a significant growth trend (p < 0.05, 0.15km³/year), attributed to the upward trend in evaporation rate (p < 0.05, 0.0046 mm/d/year) and total reservoir area (p < 0.05). The differences in economic development level and reservoir size result in significant spatial heterogeneity in the evaporation loss trend in different regions. The results can serve as a useful reference for water resources management and sustainable utilization.