Study On Climate Extreme Change And Runoff Response Of Yalong River Basin Under The Background Of Climate Change

In recent years,climate change,mainly caused by rising temperatures,has become a focus in the world.Climate change further affects runoff by affecting the spatiotemporal distribution of water resources and the process of water cycle.The Yalong River Basin is an important hydropower base in China.Studying the runoff response caused by climate change in the Yalong River Basin is significant to the development of hydropower energy sources and water resources management in the basin.In this paper,the Yalong River Basin is used as a research area,and the runoff is simulated by SWAT model.The SDSM model is used to forecast meteorological elements in different scenarios in the future.Future runoff change of Yalong River Basin is obtained by coupling two models.The results are as follows:1)Precipitation and air temperature in the Yalong River Basin vary greatly in space,increasing significantly from upstream to downstream.2)According to the analysis of extreme climate indicators from 1963 to 2016,it can be seen that the temperature difference in summer in the Yalong River basin becomes smaller and the temperature difference in winter becomes larger.The distribution of precipitation in the upstream and downstream throughout the year is gradually uniform and concentrated.The extreme precipitation index of the middle reaches and the annual precipitation in the entire basin had no mutation;the abrupt changes of the extreme precipitation index in the lower reaches and the entire basin occurred mainly in the early 21 st century.3)According to the analysis of future extreme climate index,the sensitivity of the maximum monthly precipitation to different emission scenarios is greater than the annual maximum temperature and annual minimum temperature;the maximum monthly precipitation and annual maximum temperature in the high-emission scenario,and the maximum monthly precipitation in the medium-emission scenario show a significant upward trend.The monthly maximum value of precipitation showed a significant upward trend.The monthly rainfall in the upper and lower reaches is abruptly changed in the low emission scenario,and the monthly rainfall in the middle reaches is abruptly changed in the middle and high emission scenarios.The lower the emission scenario,the more areas where the annual maximum temperature changes abruptly,and the years when the abrupt changes occur are mainly around the 1970 s.The abrupt year of annual minimum temperature is mainly around the 1930 s and 1970 s.4)The SDSM statistical downscaling model and the Can ESM2 climate model are applicable in the Yalong River Basin.The simulation of precipitation is not as good as the simulation of temperature.Under different emission scenarios,the annual precipitation and annual maximum temperature in the high-emission scenarios in the long-term period show a clear upward trend,and the climate extremes in other emission scenarios have no significant upward or downward trend;the annual precipitation upstream is reduced relative to the base period,and the annual precipitation in midstream is also(variations are-11% ?-22% and-1% ?-2%,respectively),and it is necessary to prevent the occurrence of upstream drought;the amount of annual precipitation in the downstream has increased relative to the base period(variation of 23% to 33%),and it is necessary to prevent the occurrence of downstream floods;under different emission scenarios in the future,the monthly precipitation in March to August will increase significantly compared to the base period(the largest increase is in April with an increase of 42%?51% and July with an increase of 25.8?36.4mm),which would increase flood risk during flood season,;the maximum and minimum daily temperature increased the most in January and October(16%?17% and 55%?80%,respectively).5)The SWAT model is effective on runoff simulation in the Yalong River watershed,and has good applicability in the watershed;the parameters with higher sensitivity to runoff simulation is CN2,ALPHA?BNK,SOL?AWC.6)The meteorological data from 2021 to 2100 under the RCP2.6,RCP4.5,and RCP8.5 emission scenarios were input into the already-determined SWAT model to predict the future runoff in the Yalong River basin.The analysis shows that the annual runoff under the high-emission scenario in the long-term scenario shows a clear upward trend,an increase of 10% compared to the base period,and the annual runoff under the low and medium emission scenarios decreases compared to the base period.The trends of annual runoff and maximum monthly runoff are generally consistent.The maximum monthly runoff under the high-emission scenario in the long-term period is 4% higher than the baseline period.The flood season is advanced in time relative to the base period,and the runoff in summer is increased relative to the base period,and the risk of flooding in summer is increased;the runoff in autumn is reduced relative to the base period,and the risk of drought in autumn.The area with great impact on runoff changes from the upstream to the downstream with the increase of the emission scenario.