Variation of water cycle in upper reaches of Yangtze River from 1960 to 2005

Variations of the water vapor content,water vapor flux,and water vapor budget in the upper reaches of the Yangtze River were analyzed,and a conceptual model of the water cycle was established in this study.Through analysis of the variation of water cycle parameters,the interaction and change process of the land surface branch and the atmosphere branch of the water cycle were studied.The results show that the water vapor was concentrated in the upper reaches of the Yangtze River,and the net water vapor input was 23 790 t/s.Water vapor flowed out in the latitudinal direction,and there was a significant declining trend of the water vapor flux in this direction.There was a slight variation in the water vapor budget in the upper reaches of the Yangtze River and a slightly decreasing trend of the water vapor input.Although the precipitation caused by the local evapotranspiration accounts for less than 10% of the total regional precipitation,it has an increasing effect on the local water cycle year by year.