京津冀地区7-9月极端降水分型及趋势分析OACSTPCD

This study uses the K-means clustering analysis method to classify the extreme precipitation events in the Beijing-Tianjin-Hebei(BTH)region during July to September from 1979 to 2022 into four categories according to their intensity and location.Based on this,the circulation characteristics,long term trends and their corresponding causes of extreme precipitation in the BTH region from July to September were analyzed.By analyzing the atmospheric circulation in different levels corresponding to the four types of extreme precipitation,it is shown that weather systems such as the low-level southwest airflow,the subtropical high pressure in the mid-level,the South Asian high,and westerly jet in the upper level jointly influence the extreme precipitation in the BTH region with different configurations.For long-term trends,the frequency of extreme precipitation in the BTH region shows an upward trend during July to September from 1979 to 2022.This is due to the increase in extreme precipitation of types Ⅱ and Ⅲ in July,as well as the increase in extreme precipitation of type Ⅳ in September.By analyzing the background field,it is suggested that the low-level water vapor field and the upper-level potential height field are conducive to the increase of extreme precipitation in July.The increase in extreme precipitation of type Ⅳ in September is due to the increase in background dynamic fields and geopotential height fields in the lower and upper levels.