Characteristics Of Summer Extreme Precipitation Events In Hengduan Mountains From 1970 To 2018 And Their Relationship With Large-scale Circulation

The Hengduan Mountain area,which is an important part of the longitudinal ridge valleys in southwest China,has complex topography,significant vertical changes in climate and combination of multiple climate types,it has an important impact on the climate and ecological environment in surrounding area and central-western China.Based on the daily precipitation data of the station of 50 stations in the Hengduan Mountain area in 1970-2018,the 11 extreme precipitation indexes of ETCCDI climate change indexes were chosen,the temporal variation characteristics of annual precipitation and summer precipitation,the spatial difference of extreme precipitation thresholds,the characteristics of distribution and spatio-temporal changes of extreme precipitation events were analyzed by using linear tendency estimation,M-K mutation test,Kriging interpolation method,wavelet analysis method and other methods,and the characteristics of large-scale circulation in the years of high and low extreme precipitation were analyzed by using the reanalysis monthly average data of NCEP /NCAR from June to August in 1970-2018.The results showed that:(1)The annual precipitation and summer precipitation in the Hengduan Mountain area have an evolutionary process that increases first and then decreases and then increases from around 1990 to 2018;the range of extreme precipitation thresholds and extreme heavy precipitation thresholds are 7.6-24.3mm and 19.9-81.5mm,both of which have similar characteristics that more in south and less in north,more in southeast and less in northwest.The extreme precipitation threshold and extreme heavy precipitation threshold have a positive correlation with altitude.(2)R10,R20,R50,PRCPTOT,R95 P,R99P,RX1 day,RX5day,and SDII generally have characteristics of the distribution that more in south and less in north,decreasing from southeast to northwest,Liangshan,Ya'an,Emei Mountains are the large value area of the above indexes,while Ningjing Mountain,Sharuli Mountain,Gongga Mountain and Aba Plateau are low value areas.(3)R10,R20,R50,RX5 day and CWD show a decreasing trend as a whole,PRCPTOT,R95 P,R99P,RX1 day,CDD and SDII show an increasing trend,but only R50 and SDII change significantly;the extreme precipitation index changes have obvious stage characteristics,except R99 P,RX5day and SDII,the other indexes have abrupt changes,and the year and trend of the abrupt changes are different;each extreme precipitation index has an obvious oscillation period,26 a,16a,7-8a and 3-4a are main oscillation period which appear more.(4)More than half of the stations show a decreasing trend in R10,R20,R50,RX5 day and CWD,mainly distributed in Aba Plateau,Ya'an,Leshan and Yunnan and other places,other indexes have more stations of increasing trend.(5)The water vapor in the Hengduan mountain areas in summer is mainly derived from the southwest airflow in the Bay of Bengal and the Arabian Sea,the southeast airflow in the South China Sea and the westerly wind in the middle and upper layers.The west Pacific subtropical high extends westward in higher years,enhanced transport of water vapor to the Hengduan Mountain area by the South China Sea,the abnormal anticyclone in the Arabian Sea and the Bay of Bengal.Anomalous cyclonic circulation in the Yellow Sea and East China sea region transporting water vapor in the east and northeast of the Hengduan Mountain area,causing the occurrence of extreme precipitation,the intensity and area of the South Asian high pressure are relatively large,and the ridge point is relatively eastward,resulting in increased precipitation in the west of the Sichuan Basin,making the extreme precipitation in the entire Hengduan Mountain area increase,the lower years show the opposite characteristics.