Land-Atmosphere Coupling Simulation And Analysis Of Streamflow Changes In The Yangtze River Basin

Yangze River Basin is the largest catchment in China. Due to the impact of humanactivities and climate change, river discharge and flow regime of the Yangtze RiverBasin significantly changed in recent twenty years and this change has drawn greatattention worldwide. In this study, the characteristic and the reasons for streamflowchanges in the Yangtze River Basin from past to the future were investigated using aland-atmosphere coupling simulation method.First, a distributed hydrological model was developed for the whole Yangtze RiverBasin. On the basis of this hydrological model, a land-atmosphere coupling simulationsystem was developed, which includes the hydrological model, the dynamicaldownscaling and statistical downscaling method of GCM model and a meso-scalenumerical weather forecast model. This system was applied to the streamflowsimulation in the past, short time streamflow forecast and projection of streamflowchanges in the future climate scenario.Regarding the streamflow and flow regime changes in the past50years, the dailyriver discharges in the period of1961~2009were simulated by the distributedhydrological model. A comprehensive analysis method was developed using theeco-flow metrics (ecosurplus and ecodeficit), the IHA metrics and the model simulation.Based on this method, the characteristic and the reasons for streamflow and flow regimechanges in the Yangtze River Basin in the period of1961~2009were analyzed and theimpact of the Three Gorges Reservoir on flow regime changes in the middle and lowerYangtze River was evaluated. The results showed that annual streamflow in the YangtzeRiver decreased in the past50years and the autumn streamflow significantly decreasedwhich was consistent with the decreasing trend of precipitation. Since the1990s,increase of reservoir water storing intensified the reduction of autumn streamflow. Atthe same time, winter streamflow increased which was attributed to the reservoir waterrelease since the1990s.Regarding the short time streamflow forecast, the Upper Yangtze River Basin wasselected as the study area and the objective of this study was to improve the floodprediction of the Three Gorges Reservoir. A land-atmosphere coupling method wasstudied using the meso-scale numerical weather forecast model and the distributed hydrological model. The results of the precipitation forecast experiment illustrated thatthe numerical weather forecast model showed skills in predicting the basin-averagedrainfall amount, the rainfall temporal processes and the spatial distribution of rainfall.The land-atmosphere coupling method extended the leading time for the flood forecastof the Three Gorges Reservoir and showed acceptable accuracy.Regarding the projection of streamflow changes in the future climate scenario, theskills of the dynamical downscaling and statistical downscaling method in reproducingregional climate characteristics were compared. The results showed that dynamicaldownscaling method showed higher skills than the statistical downscaling method inreproducing the heavy precipitation processes and the wet spells. The streamflowchanges in the future climate scenario were simulated by the land-atmosphere couplingsimulation system. The results showed that for the projections of streamflow changes inthe future climate scenario, the uncertainty from the GCM is larger than the uncertaintyfrom the downscaling method. The results of the mean of four GCM models showedthat the precipitation and streamflow of the Yangtze River Basin will increase in all theseasons in the future climate scenario. The annual streamflow will increase by14.4%and10.8%at the Yichang and Datong gauge, respectively.