The water resource efficiency and water-saving effect of cascade hydropower development

[Objective] The aim of this study was to reveal the pattern of change of water resource efficiency in cascade hydropower development, in order to improve the water resource efficiency of cascade hydropower development and promote water-saving development. [Methods] We employed the panel data of 22 hydropower development basins in China from 1996 to 2020, including 331 large and medium-sized hydropower stations. Using fixed effects and moderating effects models, this study analyzed the impact of the cascade hydropower development scale on its water resource efficiency, and tested the moderating mechanism of the development mode in the process. [Results] This research found that: (1) With the increase of cascade hydropower development scale, water resource efficiency showed a U-shaped trend of decreasing first and then increasing. (2) For the U-shaped correlation between cascade hydropower development scale and water resource efficiency, intensive development mode and diverse development mode all had a positive moderating effect, and diverse development mode showed a stronger positive moderating effect. (3) There was a positive correlation between basin water resource endowment and water resource efficiency of cascade hydropower development, and the diverse development mode was more conducive to strengthening this positive correlation when comparing with the intensive development mode. [Conclusion] These results prove that watershed cascade hydropower development can save water, but only when the development scale exceeds the threshold of 59%, the water-saving effect is stable and obvious. In order to promote water-saving development, intensive development mode should be implemented in the initial stage of cascade development, the diverse development mode should be implemented when the development scale exceeds the threshold, and the diverse development mode is more suitable for the rivers where water resource is scarce.