京津冀地区7—9月极端降水分型及趋势分析

Analysis of extreme precipitation patterns and trends in the Beijing-Tianjin-Hebei region from July to September

本文采用K-means聚类分析的方法,将京津冀地区1979—2022年7—9月极端降水事件按照强度和位置分为四类,并在此基础上分析了此地区7—9月极端降水的环流特征、变化趋势及可能原因。通过分析不同高度层四类极端降水对应的大气环流可知,低层的西南气流、中层的副热带高压、高层的南亚高压、西风急流等天气系统以不同的配置组合共同对京津冀地区的极端降水产生影响。在长期趋势方面,1979—2022年7—9月京津冀地区的极端降水频率呈上升趋势,这是由于7月类型Ⅱ和Ⅲ极端降水的增加,以及9月类型Ⅳ极端降水的增长所致。通过对背景场的分析发现,低层水汽场及高层位势高度场有利于7月极端降水的增加,而9月类型Ⅳ极端降水的增加则源自于低层和高层背景动力场及位势高度场的增加。

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.