Study On The Temporal And Spatial Variation Characteristics Of Typhoons And Plum Rains In The Yangtze And Huaihe River Basin And Their Encounte

The typhoon flood season and Meiyu flood season are the main flood seasons in the Yangtze-Huai River Basin,and the amount of precipitation during this period profoundly affects the drought and flood patterns in this region.Firstly,We used observed daily precipitation from239 meteorological stations over Yangtze-Huai River basin from 1961 to 2020,used OSAT method to separate the typhoon induced precipitation,and analyzes the spatiotemporal variation characteristics of typhoon precipitation days,typhoon frequency,and typhoon precipitation;Then,identify the Meiyu process according to the Meiyu Monitoring Indicators(GB/T 33671-2017),analyze the spatiotemporal variation characteristics of Meiyu characteristic quantities,and compare the spatiotemporal variation characteristics of precipitation incidence rates and precipitation contribution rates for different precipitation levels during the Meiyu period;Finally,the variation characteristics of typhoon precipitation days and typhoon frequency in different intervals before and after the Meiyu period and during the Meiyu period are analyzed,and the joint probability distribution of typhoon precipitation and Meiyu intensity during the Meiyu period are analyzed.The main conclusions obtained are as follows:(1)In the past 60 years,the multi-year average typhoon precipitation days in regions I,II,III,and the Yangtze-Huai River Basin have been 14.7,12.6,6.8,and 16.8 days,respectively.The multi-year average typhoon frequency have been 6.1,5.1,3.2,and 6.8 times,respectively,and the multi-year average typhoon precipitation have been 111.1,62.2,64.4,and 76.1 mm,respectively.The interannual differences of typhoon precipitation days,typhoon frequency,and typhoon precipitation are significant,with a single peak distribution from April to December in the year,with the maximum value achieved in August.The average number of typhoon precipitation days,typhoon frequency,and typhoon precipitation at each station over the years are 1.7 ～ 9.6 days,1.3 ～ 4.9 times,and 19.4 ～ 314.1 mm,respectively.The spatial differences of typhoon precipitation days,typhoon frequency,and typhoon precipitation are large in the southeast and low in the northwest of each region.(2)The average Meiyu onset data,ending data in region I is the earliest,followed by region II,and region III.The length of the Meiyu period in the three regions is respectively 30,30,and24 days,and the Meiyu intensity is 367.6,298.4,and 353.5 mm,respectively.The Meiyu intensity in region II presents a significant increasing trend.The Meiyu precipitation in the Yangtze-Huai River Basin is relatively large in the middle of region I and II,with the largest number of rainy days in region I,followed by region II,and the smallest in region III.During the Meiyu period,the number of light rain days and the precipitation incidence rate are the highest.The number of heavy rain days and rainstorm days in the middle and east of region II are significantly increased.The rainstorm accounts for the largest proportion in Meiyu period,and the precipitation contribution rate is also the largest.The contribution rate of light rain and moderate rain at 17 stations in the middle and east of region II is significantly reduced.(3)The number of typhoon precipitation days and typhoon frequency occurring before the Meiyu onset data in regions I,II,III,and the Yangtze-Huai River Basin are relatively small.The empirical frequencies of typhoon precipitation days occurring during the Meiyu period in the four regions are 12.7%,11.1%,11.8%,and 14.9%,respectively.The empirical frequencies of typhoon frequency occurring during the Meiyu period are 13.6%,11.7%,13.6%,and 17.4%,respectively.The number of typhoon precipitation days and typhoon frequency in four regions are relatively large after the Meiyu ending data.In region I,II,and the Yangtze-Huai River Basin,the probability of occurrence of typhoon precipitation and Meiyu rain intensity during the Meiyu period is relatively high under the scenarios of low typhoon precipitation and high Meiyu intensity.The combined recurrence period of typhoon precipitation and Meiyu rain intensity during the Meiyu period is mostly less than 5 years,and the frequency of occurrence of low typhoon precipitation and low Meiyu rain intensity is relatively high.