Study On The Spatiotemporal Characteristics Of Extreme Climate And Future Change Trend In Longtan Watershed

With global warming,the extreme climates are becoming more and more frequent,causing huge economic losses and social harmful impacts,which have aroused great concern from governments of various countries.To explore the evolution law,causes of change,simulation and early warning assessment of extreme climate events,and to carry out quantitative evaluation and description of them,has become the hot and difficult point of current research.This paper takes the Longtan watershed as the research object,based on the meteorological observation data from 1959 to 2017,using the M-K trend mutation test,Morlet wavelet,EOF analysis and other methods to explore the spatial and temporal distribution characteristics of the extreme climate in the watershed.Meanwhile,based on 11CMIP5 climate models,the simulation effects of precipitation and temperature in Longtan watershed were analyzed,and the extreme climate change in the watershed in 2021-2050 under the higher emission scenario RCP8.5 and lower emission scenario RCP4.5 was estimated.The main conclusions are as follows:(1)The trend of extreme precipitation in Longtan basin is not significant,only the numbers of continuous wet days(CWD)passed the significance test after 2010,showing a decreasing trend.The maximum consecutive 5 days of precipitation(RX5D)showed an insignificant decrease trend,and the remaining extreme precipitation indices showed an insignificant increase trend,but all fluctuated obviously in the 1960 s.The change of extreme temperature is more significant,the index related to warm is increasing significantly,the cold day index(TX10p)and cold continuous day index(CSDI)are not decreasing significantly,the daily temperature range(DTR),frost day number(FD)and cold night index(TN10p)are decreasing significantly.The abrupt trend of extreme precipitation is not obvious,and the significant trend of extreme temperature index has mutations,mainly occurred in the 1980 s,1990s and after 2000.The cycle characteristics of extreme precipitation and extreme temperature are significant,and there are multiple time scales.The first main cycle is mainlyin the range of 5-9A,11-19 a and 23-30 a.(2)In space,the spatial distribution of most extreme precipitation and extreme temperature is increasing or decreasing from southwest to northeast,and the fluctuation is obvious with the alternation of positive and negative position of time.Most of the spatial variation features are spatial consistency or more in southwest,less in Northeast and less in southwest,more in Northeast.There are spatial characteristics of decreasing trend of frost days(FD)and extreme minimum temperature(TNn)from south to north.(3)Under the return period level of 5,20 and 50 years,the daily maximum precipitation(RX1d),the continuous 5-day maximum precipitation(RX5d),and the heavy precipitation(R5p)index are increasing from upstream to downstream,with great difference in spatial precipitation;the extreme maximum temperature(TXx)in most areas is above 30 ?,and the high value areas are distributed in the north,and the TNn only appears zero temperature once in 5 years,It is distributed in Southwest China.Under the same return period,the spatial differences of warm day index(TX90p),warm night index(TN90p)and cold day index(TX10p)were significant,while the spatial differences of cold night index(TN10p)were not significant.(4)The simulation effect of CMIP5 climate model on temperature is better than that of precipitation.In the next 30 years,under the RCP4.5 emission scenario,the precipitation intensity(SDII)index in most areas of the basin shows no significant increase trend;TXX and TNn change significantly,compared with the reference period 1961?1990,TXx and TNn index increased by 2.1? and 0.5? respectively,and TNn index increased significantly at the rate of 0.58?0.76?/10 a.Under the RCP8.5 emission scenario,the interannual change of the SDII index increased in the southwest region and decreased in the northeast region,and showed the spatial distribution characteristics of more in the Northeast than in the southwest;The TXx and TNn increase by 2.5 ? and 0.8 ? respectively,respectively,and the annual increase rate in the east was higher than that in the west,TXx showed a high distribution from east to west,and TNn showed a low distribution from south to north.