Research On Optimal Operation Of Joint Water Supply Of Cascade Reservoirs In The Upper Reaches Of The Hanjiang River Under The Impact Of Climate Change

Climate change will alter the global hydrological cycle,which would have some impact on water resources distribution in time and space.The existence of uneven distribution of water resources in time and space and uneven water demand of human society makes inter-basin water transfer projects an important way to alleviate or even solve the water shortage in water-deficient areas.Focusing on joint water supply operation of cascade reservoirs under the impact of climate change,this paper takes the upper reaches of the Hanjiang River as example,and the Danjiangkou Reservoir is the core of research on joint water supply operation of cascade reservoirs under different climate change scenarios.Firstly,a GCM-XAJ model based on the interconnection of global climate model and Xin’anjiang model is constructed,and runoffs of five dam sites(Ankang,Shiquan,Pankou,Huanglongtan,Danjiangkou dam sites)in the upper reaches of the Hanjiang River for the next 30 years(2021-2050)under three climate change scenarios(RCP 2.6,RCP 4.5,RCP 8.5)and five global climate models(GFDL-ESM2M,HADGEM2-ES,IPSL-CM5A-LR,MIROC-ESM-CHEM,NORESM1-M)are predicted and its trend under climate change is assessed.Then a joint optimal operation model of cascade reservoirs in the upper reaches of the Hanjiang River is constructed,and the maximum total water supply of Taocha and Qingquangou in different standard years(2020,2030standard years),different water-transfer modes(without considering and considering the water diversion of the Hanjiang-Weihe Project),different inflow frequencies(P=10%,P=50%,P=90%)and different start water levels of the Danjiangkou reservoir(z=150m,z=155m,z=160m,z=165m,z=170m)are calculated,the impact of the water diversion of the Hanjiang-Weihe Project and the guarantee rate of Taocha and Qingquangou water supply is evaluated.Finally,based on results of 15 runoffs and 900 optimal operation schemes,the uncertainties of future runoff change and maximum water supply variation interval of cascade reservoirs under different climate change scenarios are analyzed,and the impact of the water diversion of the Hanjiang-Weihe Project and variation of the guarantee rate of Taocha and Qingquangou water supply under climate change are evaluated.Main conclusions are as follow:(1)Despite the high uncertainty of future runoff prediction under climate change,GCM-XAJ prediction results are still of great significance as reference.Under the climate change scenarios of RCP 2.6,RCP 4.5 and RCP 8.5,the annual runoff of the upper reaches of the Hanjiang River has a downward trend.Compared with the benchmark year(1961-2000),the average annual runoff of the upper reaches of the Hanjiang River will decrease by 4.3%,3.0%and 8.3%in the next 30 years,respectively.(2)After considering the water diversion of the Hanjiang-Weihe Project,in 2020standard year,the maximum reduction of water supply of cascade reservoirs at the frequencies of P=10%,P=50%and P=90%is 88 million m~3,133 million m~3,135 million m~3;in 2030 standard year,the maximum reduction of water supply of cascade reservoirs at the frequencies of P=10%,P=50%and P=90%is 99 million m~3,137 million m~3 and288 million m~3.The water diversion of the Hanjiang-Weihe Project has little impact on the optimal operation of joint water supply of cascade reservoirs.Not considering the water diversion of the Changjiang-Hanjiang Project,in 2020 standard year,the guarantee rate of Taocha and Qingquangou water supply is 97.19%and 100%,respectively,in 2030standard year,the guarantee rate of Taocha and Qingquangou water supply is 44.86%and98.43%,respectively.(3)Under the climate change scenarios of RCP 2.6,RCP 4.5 and RCP 8.5,the annual runoff variation interval of the five global climate models is with high uncertainty,its average length of variation interval is 18.2%,33.1%and 30.2%,respectively.In 2020and 2030 standard years,the relative change of variation interval of the maximum water supply of cascade reservoirs is 12.53%and 7.74%,respectively,with high uncertainty.Under the impact of climate change,the water diversion of the Hanjiang-Weihe Project has little impact on the optimal operation of joint water supply of cascade reservoirs,and the guarantee rate of Taocha and Qingquangou water supply also change little.