Abstract: The cascade hydropower construction along the Jinsha River has altered downstream water temperatures, significantly impacting fish reproduction and growth. Utilizing surface water temperature monitoring data spanning from 2002 to 2022 at Xiangjiaba, Zhutuo, Yichang, and Datong hydrological stations, we compared the variations in water temperature downstream of the cascade reservoirs between construction period and operational period. Our findings reveal that: 1) During the two-stage joint operation of Xiangjiaba and Xiluodu hydropower stations, the annual minimum water temperature at Xiangjiaba hydrological station rose by 1.4 ℃, with the occurrence of the lowest water temperature delayed by 35 days compared to natural conditions. 2) Subsequent to the construction of Wudongde and Baihetan hydropower stations and the shift to four-stage joint operation, the lowest water temperatures at Xiangjiaba, Zhutuo, Yichang, and Datong hydrological stations increased by 2.0 ℃, 1.1 ℃, 0.8 ℃, and 0.7 ℃, respectively, compared to the two-stage operation period. Additionally, the occurrence of the lowest water temperature with four-stage operation was delayed by approximately 42 days, 29 days, 11 days, and 18 days, respectively. These results offer valuable scientific support for managing water temperatures in cascade reservoirs and safeguarding downstream eco-environments.

Key words: downstream of Jinsha River, cascade hydropower projects, water temperature, flattening effect, delay effect