Spatio-temporal Characteristics And Projection Of Extreme Precipitation In Hanjiang River Basin

In the context of climate change,since 1963,the proportion of extreme precipitation to annual precipitation in the Hanjiang River Basin and the extreme precipitation threshold show an increasing trend.To some extent,the extreme precipitation trend has increased the risk of meteorological disasters.The Hanjiang River is the largest tributary of the Yangtze River,and its upstream is the water source of the Middle Route of the South-to-North Water Diversion Project,which plays an important role in the overall pattern of regional development.Therefore,the study on the trend of extreme precipitation in the Hanjiang River Basin under the background of climate change is of great significance to the water resources,trans-regional water diversion and sustainable development of the Hanjiang River Basin,as well as the response to regional climate change and the work of disaster prevention and mitigation.Although many scholars have analyzed the change characteristics of extreme precipitation in the Hanjiang River Basin from different perspectives and obtained certain research results,a comprehensive perspective and the research on the projection of extreme precipitation in the Hanjiang River Basin is limited.In order to make a more comprehensive study of the variation of extreme precipitation in history and under climate change scenarios,a gridded daily observation dataset CN05.1 from National Climate Center was used to analysis the variability of extreme precipitation from1961 to 2014 and extreme precipitation in flood season.Besides,based on the daily precipitation data of five global climate models from the Inter-Sector Impact Model Intercomparison Project(ISIMIP),the model simulation ability were evaluated,and the intensity,frequency and duration indices were calculated,the variation of extreme precipitation as well as the uncertainty of projection in Hanjiang River Basin from 2020 to2099 under the scenarios of RCP2.6,RCP4.5 and RCP8.5 were analyzed.Main conclusions were drawn as followings:(1)In the historical period,the precipitation indices are relatively high in the early1960 s,1980s,early 1990 s and early 21 st century.On the whole,the fluctuation of extreme precipitation indices in the Hanjiang River Basin is obvious in historical period,but intensity indices are insignificantly increased,The total number of days with annual precipitation greater than 10mm(R10)and the continuous wet days(CWD)are insignificant decreased,and the total number of days with annual precipitation greater than 20mm(R20)and the total number of days with annual precipitation greater than 50mm(R50)show an insignificant increasing trend.According to the projection,except for the CWD under the scenario of RCP8.5,the indices show increasing trends of growth under the three scenarios.Most of the trends under the scenario of RCP2.6 are not significant,but the trends under the scenario of RCP4.5 and RCP8.5 are significant.Besides,it can be found that the higher the emission concentration is,the more obvious the change index is.(2)From spatial variation perspective,the southwest region,near Zhenba district and the downstream region from Zhongxiang district show the most significant change,max 1 day precipitation amount(RX1d),max 5 day precipitation amount(RX5d),extreme rainfall(R99p),simple daily intensity index(SDII),R20 and R50 are most significantly increased in these regions,and R10 is most significantly reduced in these regions.These phenomena indicate that the variation range are generally larger in the southeast and southwest regions,where the annual total precipitation are larger,and the trends of extreme precipitation are more obvious.About spatial variation in the future,the intensity indices in the downstream region from Zhongxiang district decreased most under RCP2.6 and RCP4.5 scenarios.The spatial variation characteristics can be summarized as the characteristics of "bigger change in the eastern and western parts and little change in the middle parts",such as RX1 d,R99p and SDII,or the characteristics of "decrease in the eastern and western parts and increase in the middle parts",such as RX5 d.Under RCP8.5 scenario,as time goes by,the area where the intensity indices increase start to expand.In different scenarios,the downstream region from Zhongxiang district is area with the largest variation,and the Zhenping and Zhenba distircts in the southwest of the basin are the regions with large variation.(3)About projection uncertainty,the uncertainty of CWD is the largest under RCP4.5scenario,and the uncertainty in the other indices are largest under RCP8.5 scenario.Spatially,the uncertainty of intensity indices are greater in the eastern part of the basin than in the western part,the uncertainty of frequency indices are greater in the northern part of the basin than in the southern part,and the uncertainty of CWD is greater in the east region of Nanyang district and the downstream region from Zhongxiang district.