Changes in climate and runoff in the middle course area of the Yarlung Zangbo River Basin

Based on monthly data for precipitation,air temperature and runoff in and around the middle course area of the Yarlung Zangbo River Basin from 1956 to 2010,changes and runoff responses were analyzed quantitatively using wavelet analysis,correlation analysis,and multiple linear regression. We found that warming is obvious in the study area,showing that the average rate of warming is 0.31°C/10 a. Trends in precipitation and runoff are highly consistent,showing a fluctuation of increase-reduce-increase-reduce. The periodic change in interval runoff and precipitation maintains a high level of consistency and at two scales of 6.0~6.5a and 15.5~16.5a,however,temperature change periodicity is weak. Precipitation is the most dominant factor controlling changes in annual runoff and the correlation coefficient was 0.89 between precipitation and runoff;however,both air temperature and precipitation are impacting runoff processes within a year,and the runoff response shows hysteresis. Generally,runoff is the result of precipitation from June to November,and air temperature has a positive effect on runoff in other periods. The magnitude of precipitation determines runoff from April to September,and as a result the runoff coefficient is below 1.0. In contrast,the runoff coefficient is much larger than 1.0 during other months because river feeding takes place,rather than precipitation. With climate warming and wetting,the runoff coefficient is gradually decreasing,indicating that the influence of factors other than precipitation on runoff is increasing in the area.