Water Cycle Evolution In The Upper Reach Of Yangtze River Basin Under Climate Change

Global warming may speed up the water cycle and affect the atmosphere generalcirculation which r esults in change of the te mporal a nd spatial di stribution andintensity of rainfall, hydrological process, evaporation, infiltration and runoff. Also,global warming will increase the frequency and intensity of drought, floods and otherextreme climate, affecting local social and economic development. The Yangtze riverbasin i s t he i mportant r egion f or economic de velopment and key area of w aterresources utilization in our country, especially the upper reach of Yangtze River, soabnormal fluctuations caused by global warming can, on the one hand, break balancebetween the original river runoff and the flood control and disaster alleviation system,causing flood disasters; On the other hand, changes of rainfall and runoff will bringnew problems on the water resources utilization.The paper first established the distributed hydrological model in the upper reachof Yangtze River, then downscaled and forecasted the c limate variables of G CMbased on the statistical downscaling method, which will be used as input of distributedhydrological model so as to get the hydrological response under different scenarios inthe upper reach of Yangtze River and analyze the impact on water regime and waterresources which will provide reference and basis for reasonable exploitation a ndutilization, the main results and conclusions are as follows:(1) Based on the long series (1961-2000) measured data and distributed hydrologicalmodel EasyDHM, distributed hydrological model in the upper reach of Yangtze Riverwas established with calibration a nd ve rification. Results s how tha t s imulationaccuracy of the model on the upper reaches of Yangtze River basin is relatively high.(2) After e stablishing the dow nscaling m odel f or meteorological e lements of67stations in the upper reach of Yangtze River by the SDSM model, the calibration andvalidation of t he m odel were done a nd t he r esults indicate t hat the m odel c ouldsimulate the change of meteorological elements such as temperature and rainfall well.(3)The s tatistical dow nscaling mod el a nd the di stributed hydrological model werecombined to predict the future runoff changes. The results show that total runoff ofYichang hydro station in the upper Yangtze River is likely to decrease as a whole inthe next90years. In the first next30years, the runoff will be higher than the averagehistory (1961~2005)value, and closer to it in the second next30years, then continueto decrease in the third30years (2070~2099)both in A2and B2scenarios with littlerange.