Exploring And Projecting The Impact Of Environment Change On Hydrology And Water Resources In The Upper Reaches Of The Yangtze River Basin

In the past 50 years,global warming speeds up the hydrological circle and affects the atmospheric circulation which results in change of watershed hydrological processes and temporal-spatial distribution law of water resources.Increasingly frequent extreme climate events have become the hot topic for the international community.The Yangtze River originated in the Qinghai Tibet Plateau in Chinese,flows into the East China Sea,with a total length of 6300 km,is the longest river on the Eurasian continent.The Yangtze River basin is a key area of water resources utilization in our country,and the upper reach of Yangtze River is particularly important.Climate changes caused by global warming,will tip the balance between the current temporal-spatial water resources distribution and flood control system.The complex topography,typically monsoon climate and unevenly spatial and temporal distribution of annual precipitation and rainstorm make the drought and flood disasters frequently,which brings new problems for effective use of water resources.The scientific assessment of the multidimensional response of water cycle and its trend prediction in the upper reaches of the Yangtze River Basin will be of guiding significance to disaster prevention and reduction,eco-civilization construction,economic and social sustainable development.In this thesis,we focus on the response of runoff to the changing environment in the upper reaches of the Yangtze River basin.The current research could provide important scientific and theoretical support for the evolution situation analysis and optimal utilization of water resources.Therefore,it has profound theoretical significance and great engineering practical value for both reducing flood/drought disaster losses and achieving the sustainable utilization of water resources.The main achievements and innovations of the current paper are as follows:Based on the long term meteorological and hydrological data,the spatiotemporal variability of water cycle factors in the upper reaches of the Yangtze River was studied.The Mann-Kendall trend analysis and Mann-Kendall mutation detection method were perfored to identify the spatiotemporal variability of climate and streamflow.R/S analysis method and cumulative hyperbolic method were performed to predict the future climate change.The results explored the changing characteristics of the hydrological and meteorological elements and its changing trends in the Jialing River Basin.The biggest threat result from global warming is not a change in average temperature but an increase in extreme weather.Owing to its the slow development and unpredictable,drought events have caused great disaster to economic activities,human activities and natural environment.To explore the spatial and temporal changes of climatic and hydrological droughts and the relationships between them,the SPEI and SDI at different time scales are assessed both at the entire Jialing River basin and at the regional levels of the three sub basins.The SPEI and SDI were firstly applied to analyze the temporal and spatial evolution of climatic and hydrological droughts for different time scales respectively.Furthermore,the results of the SPEI and SDI were used together to analyze the relationships between climatic and hydrological droughts in the whole basin and sub basins.The research focuses on the relationships between climatic drought and hydrological drought,thus to provide some early warning information for water resources department when climatic drought is happening.The possible impacts of human activities are analyzed in a simple way.A hybrid model considering the effects of climate change and human activities was proposed.The model applies the distributed variable infiltration capacity(VIC)model to simulate the runoff process under climate change,uses wavelet neural network model(WNN)to represent the routing process affected by human activities,uses binary gravitational search algorithm(BGSA)to search the the optimal number of hidden layer nodes of WNN model and the optimal wavelet input sequence.Based on the model,we simulated the runoff process in the Jinsha River Basin.Comparing to the traditional VIC model,ANN model,VIC&VIC&WNN model,the proposed hybrid model achieve better results.In this study,a physically-based modified grid-Xinanjiang model was established.A physically-based two-source potential evapotransiration model was used to calculate potential evapotranspiration.The SCS-CN model was used to evalute the values of soil water capacity and the tension of water capacity.The priori parameter method and the optimization algorithm were used jointly to detemine the the optimal value of paremeters,which can reduce the problem of parameter-heterogeneity.The infiltration excess and saturation excess runoff mechanisms were implemented to simulate the runoff process and the nonlinear Muskingum model was used to simulate the routing process.The modified Xinanjiang model can reflect the physical characteristics of basin and expand the regional applicability of rainfall-runoff simulation.The model is applied to the Jinsha River of the upper reaches of the Yangtze River Basin.Comparing to the traditional grid-Xinanjiang model,the results showed that the model performed satifactory in semi arid and semi humid area and peak-simulation was also improved in the moist area.Based on the meteorology,DEM and soil cover data,a distributed VIC model was built in Jialing River Basin.Through the parameter calibration and model validation,the simulation results showed that the VIC model has a good feasibility in the Jialing River basin.SDSM model was used to downscale three global climate models(GCMs)under the three scenarios of RCP2.6,RCP4.5 and RCP8.5.The downscaled meteorological elements were input into VIC model to analyze the hydrological response of Jialing River Basin under changing environment.The results indicated that temperature(maximum temperature and minimum temperature)of future will continue to increase especially in summer and winter,and the temperature under RCP8.5 scenario increase fastest.The future runoff and rainfall will change consistently,relatively more complicated than temperature,they overall decreased first and then increased.In the future,the outflow will be more stable in different scenarios in April,but streamflows of January,February,July and Auguest may fluctuate greatly,therefore,the hydrological disaster(droughts or floods)will occur frequently.