湖南雨季小时极端降水的特征及其对暴雨贡献分析

Characteristics of hourly extreme precipitation and its contribution to rainstorms during the rainy season in Hunan Province,China

摘要:

湖南是中国南方典型多雨省份,境内洞庭湖为中国第二大淡水湖。近年极端降水事件不断增多,由于其显著的日变化特征,预报难度大。本文利用2012—2021年湖南1 599个区域自动气象站逐小时降水观测资料,开展了湖南省雨季(4—9月)小时极端降水与12 h暴雨时空分布特征分析,以及小时极端降水对12 h暴雨的贡献率研究。结果表明:湖南雨季第99.9百分位小时极端降水高频区主要分布在雪峰山脉和南岭山脉一带以及洞庭湖区域,复杂地形和下垫面对小时极端降水频次和强度均有明显增强作用。湖南雨季小时极端降水总频次呈波浪式增长,2021年发生频次最多,5—8月为小时极端降水高发月份,其中6月为第一峰值。小时极端降水频次的日变化呈明显双峰结构,峰值分别出现在傍晚18时和早上07时。12 h暴雨发生频次空间分布与小时极端降水相似,年均频次为夜间2 490次,白天2 039次,日变化表现为夜间高于白天,5—7月为发生频次最多月份。洞庭湖区域12 h暴雨6、7月发生频次最高,高值区主要在河湖冲积平原。白天小时极端降水对12 h暴雨的降水量贡献比夜间大,高贡献率(70％～90％)的站点也更多,贡献率大值区均集中在湖南南部。

Abstract:

Hunan Province,located in southern China,experiences frequent and intense precipitation,especially during the rainy season.Recent years,have seen an increase in extreme precipitation events,characterized by significant diurnal variation,which complicates forecasting efforts.Over the past decade,China has developed a regional network of high-resolution,fully-automated weather stations,enhancing the study the study short-duration heavy rainfall.This study utilizes hourly precipitation data from 1 599 automatic weather stations across Hunan Province,collected from 2012 to 2021,to analyze the characteristics of hourly extreme precipitation during the rainy season (April—September).The study also examines the relationship between hourly extreme precipitation events and 12-hour rainstorms,focusing on their statistical characteristics and the contribution of hourly extreme events to overall rainstorm totals.This quantitative analysis aims to reveal the intrinsic connections between these events and provide a technical foundation for improving nowcasting and early warning systems.The 99.9％ percentile was selected as the threshold for defining extreme hourly precipitation in Hunan.Results show that the spatial distributions of frequency and intensity of extreme precipitation events are similar,with high-frequency areas concentrated in the Xuefeng Mountains,the southern Nanling Mountains,and the Dongting Lake area,with maximum values in southern Hunan.Complex terrain and underlying surfaces significantly enhance hourly precipitation intensity.The annual frequency of extreme hourly events in the rainy season exhibits wavelike growth,peaking in 2021 and reaching a low in 2013,where 2021 recorded nearly 90％ more events than in 2013.Extreme precipitation events are most common from May to August,peaking in June.Diurnally,extreme precipitation follows a bimodal pattern,peaking at 18:00 and 07:00 BST,with a rapid increase in the afternoon,a peak in the evening,a gradual decline overnight,and a secondary peak in the early morning.The spatial distribution of 12-hour rainstorm is similar to that of hourly extreme events,with an average annual frequency of 2 490 occurrences at night and 2 039 during the day,indicating a higher nighttime frequency.High-frequency areas for 12-hour rainstorms are found primarily in western Hunan,along the Xuefeng and Wuling Mountain ranges,with isolated high-frequency locations in the eastern and southern regions,while lower frequencies are observed between 25.5°N and 26.5°N.Monthly and daily variations in 12-hour rainstorm frequency show distinct regional patterns,with high-frequency zones varying from May to September and the Dongting Lake region experiencing the highest frequency in June and July.Daytime hourly extreme precipitation contributes significantly more to 12-hour rainstorms than nighttime events:in the daytime,41％ of stations report that hourly extreme events contribute 70％—90％ of 12-hour rainstorm totals,while this contribution rate is only 25％ at night.High-contribution regions are primarily concentrated in southern Hunan.