Abstract: Affected by multiple factors such as climate change, cascade reservoir operation, and tributary influx, the temporal and spatial distribution of water temperature in the segment of the Yangtze River from Panzhihua to Yichang has changed remarkably, which will surely have a profound impact on the river ecosystem. The water temperature data in nearly 60 years(1956-2016) of typical hydrological stations in mainstream and tributary were selected for analysis. The characteristics of spatial-temporal variation and distribution of water temperature along this segment were studied by using attribution analysis and multi-scale comparative analysis. Results revealed an apparent warming trend in the mainstream of Panzhihua-Yichang segment, while in the tributary Minjiang River, as affected by air temperature, the water temperature underwent a continuous drop by 1 ℃ between 1956 and 1990, and then gradually recovered. The range of the water temperature during a year decreased annually, with a declining range of 0.38-1.46 ℃ per decade, which means that the process of water temperature during a year tends to flatten. The construction of cascade reservoirs reduced the water temperature in the downstream rivers in spring and summer while increased in autumn and winter at Pingshan and Yichang stations. The changes in April and December after the impoundment were the largest, amounting to -2.6 ℃ and 4 ℃, respectively. The distribution pattern of water temperature along the stream was generally stable: the water temperature of the Panzhihua-Pingshan segment increased ceaselessly by 2 ℃; affected by large amount of low-temperature water (occupying over 50% of the discharge) from the Minjiang River, the water temperature of the Pingshan-Zhutuo segment dropped by 0.6 ℃; the high-temperature water in the Jialing River and the low-temperature water in the Wujiang River have little impact on the water temperature of the Zhutuo-Yichang segment due to small proportion of discharge.

Key words: Panzhihua-Yichang River segment, water temperature, spatio-temporal variation, cascade reservoirs, mainstream and tributary