Abstract: As the source area of the Yangtze River,the upper Jinsha River is of special eco-environmental functions.The water temperature of the river is of great significance to the growth of aquatic organisms and the surrounding ecological environment.In this paper,the intra-annual and inter-annual changes as well as distribution along the flow direction of natural water temperature of the upper Jinsha River were examined according to measured water temperature data from hydrological stations of Gangtuo,Batang,and Shigu.Major hydrological and meteorological factors that affect the water temperature were also analyzed.Results unveiled that the monthly average water temperature at Gangtuo,Batang,and Shigu hit the highest from July to August in general,while the lowest in January.The annual water temperature at the three stations displayed a significant upward trend from 1961 to 2018,with abrupt changes in 1998,1992,and 2003,respectively.Air temperature had the largest influence on the monthly average water temperature,followed by precipitation and streamflow;relative humidity,evaporation and wind speed also had a certain impact on the change of water temperature;sunshine hour bore a weakest relationship to water temperature.From the upstream to the downstream,the coefficients of correlation between water temperature and runoff,wind speed,and water surface evaporation decreased,while those between water temperature and precipitation,temperature,and relative humidity increased.The hydrological and meteorological characteristics of the basin were closely related with water temperature changes.In addition,the main factors affecting water temperature were further verified through principal component analysis.

Key words: water temperature, streamflow, air temperature, principal component analysis, upper Jinsha River