Quantitative Assessment Of Climate Change Impacts On Hydropower Generation In Cascade Reservoirs In The Upper Reaches Of The Yellow River

Climate has direct or indirect effects on hydrological cycles,with global warming,the incidence of extreme heat and extreme precipitation increases greatly,which seriously damages the runoff process in the hydrological cycle.For the area with high utilization degree of water energy resources,the uneven runoff process caused by climate change will lead to difficulties in the utilization of water energy resources.Many hydropower stations in the Yellow River basin,especially in the upper reaches basin,such as Longyangxia,Laxiwa,Gongboxia,Liujiaxia,which has a high sensitivity to climate change.Climate models are the basic tools to study climate change,but different climate models have different predictions of future climate change The CMIP6climate model puts forward different future carbon emission scenario assumptions according to different social development strategies,and predicted climate change according to different future carbon emission scenarios,such as SSP126,SSP245,SSP370 and SSP585,represent the future scenarios of low,medium,medium and high carbon emissions.At present,CMIP6 has been widely used in future climate change prediction and other related studies.In this thesis,the monthly runoff process in the future(2025-2100)is calculated by using measured meteorological data and corrected CMIP6 climate model data to drive the WEP-L hydrological model,based on the monthly runoff,the guaranteed output and multi-year average power generation of cascade reservoirs in the upper reaches of the Yellow River above Lanzhou are calculated by means of equal flow regulation method to explore the impact of climate change cascade reservoirs’power generation in the upper reaches of the Yellow River,the main conclusions are as follows:(1)In the study area,both precipitation and air temperature in the future(2025-2100)show an increasing trend,and the trend of air temperature change is obvious.Compared with the original CMIP6 data,the average absolute error MAE of simulated precipitation,temperature and measured data after correction is less than 2.12 mm and3.79℃,and the absolute average daily deviation MAD is less than 0.076 mm and0.060℃.The distribution of measured meteorological data is similar in spatio-temporal scale,and the correction effect is good.The future annual mean temperature’s linear tendency rate is 0.072℃/10a,0.32℃/10a,0.65℃/10a and 0.84℃/10a under the four emission scenarios of SSP126,245,370 and 585,respectively,the linear trend rate of future mean annual precipitation also increased with the increase of discharge scenario,from SSP126-SSP58,6.37mm/10a,13.81mm/10a,18.98mm/10a,23.35mm/10a,indicating that the upper reaches of the Yellow River’s future climate will have a warm and wet trend,and with the increase of carbon emission scenario,the rate of warming and wetting accelerated.(2)Climate change will promote the growth of runoff in the study area.Compared with the measured monthly runoff in the four hydrological stations of Tang Naihai,Guide,Xunhua and Lanzhou simulated by the WEP model from 1980 to 2016,the Nash coefficient NSE and the coefficient of determination R2 were all over 0.79 and 0.83respectively in the Calibration period.The Nash coefficient NSE and the coefficient of determination R2 were all over 0.71 and 0.81 respectively in the verification period.The simulation accuracy of the monthly runoff process is high and the results are reliable.In the future(2025-2100),runoff in the study area will increase under different emission scenarios,taking Tangnahai Hydrological Station as an example,in the discharge scenario from low to high,the average runoff in the future years will increase by 2.484 billion m~3,3.621 billion m~3,2.215 billion m~3 and 6.028 billion m~3,respectively,by 12.25%,17.85%,10.92%and 29.72%,compared with the historical multi-year average runoff.(3)The future climate change will promote the power generation of the cascade reservoir.Under different discharge scenarios,the guaranteed output of Longyangxia reservoirs,Liujiaxia reservoirs and Long-Liu cascade reservoirs in the future(2025-2100)will increase by 9.12%-24.48%,8.54%-35.91%and 8.82%-30.34%,respectively,compared with the historical period,the annual average power generation will increase by 10.87%-35.68%,6.49%-50.65%and 8.63%-43.32%.