Water temperature response to cascade development in Panzhihua Reach of Jinsha River

Hydropower development in the Jinsha River Basin has altered the natural thermal regime of the river, thereby adversely affecting the habitat of aquatic organisms.To investigate the water temperature response to cascade development in the Panzhihua Reach of the Jinsha River, water temperature data from the Panzhihua and Sanduizi hydrological stations were analyzed by trend tests, piecewise linear regression, and regression discontinuity design methods.The study examined the interannual, intra-annual, and longitudinal variations of water temperature in the Panzhihua Reach, with a focus on assessing the impact of impoundment by the Guanyinyan Reservoir and other cascade reservoirs (referred to as Guanyinyan impoundment) on water temperature downstream of the dam.The results showed that: ① Over the past 50 years, the mean annual water temperature in the Panzhihua Reach increased significantly (P < 0.05).After 2012, the longitudinal trend of water temperature exhibited a significant turning point, with water temperature upstream of the Yalong River confluence being significantly higher than that downstream of the confluence.② Guanyinyan impoundment exerted a significant impact on water temperature downstream of the dam (P < 0.05).Specifically, the intra-annual distribution of water temperature tended to flatten, with a pronounced "heat retention effect" in autumn and winter and a pronounced "cold retention effect" in spring and summer.The degree of temperature flattening downstream of the Yalong River confluence was greater than that upstream of the confluence.These findings provide scientific basis for ecological dispatching and the protection of fish breeding and habitat environments.