Analysis On The Characteristics And Influence Factors Of Regional Extreme Precipitation In Jiangnan Region

With global warming,the frequency and intensity of extreme precipitation show an upward trend.The occurrence of regional extreme precipitation events is related to the mesoscale weather system,and its long duration and high intensity tends to lead to regional floods.At present,the research on regional extreme precipitation has attracted the attention of experts and scholars.Based on the daily precipitation data of 299 meteorological stations in Jiangnan region from 1961 to 2018,the paper first uses percentile threshold method to determine the regional extreme precipitation,and confirms the type of regional extreme precipitation through the interpretation of weather map,and then analyzes the temporal and spatial distribution characteristics of various regional extreme precipitation by the linear trend analysis and Mann-Kendall mutation test.Finally,analyze the evolution characteristics of various extreme precipitation circulations and their possible influencing factors.Conclusions are as follows:(1)604 regional extreme precipitation events(REP)occurred in the Jiangnan region from 1961 to 2018,which were classified as 336 frontal extreme precipitation events(FEP),106 cyclonic extreme precipitation events(CEP)and 162 other extreme precipitation events(OEP).FEP most often occurs in spring,while CEP and OEP most often occur in summer.Except for the declining trend of OEP,the precipitation and days of the other two types show a significant increasing trend,it can be known that the increase of REP may be caused by the increase of FEP and CEP.FEP is mainly distributed in the higher terrain areas such as Wuyi Mountains and Nanling Mountains,while CEP is mainly distributed in the southeast coast.The distribution of various extreme precipitation of high frequency and extreme precipitation intensity high value areas is relatively consistent.(2)When FEP occurs,the atmospheric pressure in the Jiangnan region changes greatly,and the Northwest Pacific Subtropical High is westward,and the cold and warm air flows converge Jiangnan region.There was a warm anomaly near the ground in the southwest,and a cold anomaly in the northeast.In the vertical direction,the upper cold and the lower warm structure is presented.The pressure of CEP is lower in Jiangnan region,and the subtropical high moves to the north and east,showing a structure of warm upper part and cold lower part.When OEP occurred,the cold anomaly in the northeast invaded the Jiangnan region and changed the original warm anomaly in the near ground to the cold anomaly.The three types of extreme precipitation require water vapor of different sources.In addition,the anomalous water vapor convergence area of OEP and FEP spans the widest from east to west,while the north-south span is relatively smaller,and the precipitation is distributed in a zonal pattern extending from east to west.(3)Compared with the air flow on the meridional section,the air flow on the zonal section is greatly affected by the topography.FEP is mostly concentrated on the windward slope,and CEP is less affected by the terrain in the east and more affected by the terrain in the west.The effect of topography on OEP is not obvious.(4)The change of extreme precipitation with temperature is seasonal and regional.The change structure of extreme precipitation at each percentile with temperature in spring and autumn is a single peak type,and the turning points of extreme precipitation are all located at 23?24?.The extreme precipitation in each percentile in summer increases first and then decreases with the increase of temperature,and increases with the increase of temperature in winter.In addition,stations with a positive correlation between the number of FEP and their average temperature were distributed in the north of Jiangnan region,while those with a negative correlation were mostly distributed in the south.The number of OEP mostly decreased with the temperature increasing.(5)FEP and OEP are significantly affected by various subtropical high indexes,especially the Northern Hemisphere subtropical high.The response of each type of extreme precipitation to SST in different sea areas is different.NINO 1+2,A and B are the key sea areas of affecting FEP,and NINO 1+2,C and B are the key sea areas of affecting CEP.When the SST rises abnormally,FEP and CEP's days and precipitation increase abnormally.Except for NINO W,the extreme precipitation intensity of OEP decreased significantly when the SST in other sea areas increased abnormally.