2023年华北热浪-强降水连续极端事件的成因及可预测性分析

Mechanism and Predictability of Extreme Events of Consecutive Heat Waves and Heavy Precipitation in North China in 2023

  • 摘要: 全球气候变暖导致热浪和强降水事件日益增多,这两类高影响天气叠加会造成更严重的影响,亟需对二者的叠加进行研究。利用地面气象站气温和降水资料、ERA5和NCEP/NCAR再分析资料和国家气候中心发布的资料,从天气尺度分析了2023年华北地区热浪-强降水连续极端事件(the Consecutive Heat Wave and Heavy Rainfall事件,简称“CHWHR事件”)的演变特征和成因,并基于历史上多个类似事件个例,从可预测性角度,讨论了能否发生CHWHR事件的关键大气环流特征。结果发现,本次事件由2次热浪和2次强降水事件组成,前后跨度41 d。其特点是先出现2次热浪,紧接着热-湿急转进入强降水期,20 d内出现2次强降水事件。就热浪事件而言,2次热浪持续时间长,20 d内有13 d超过阈值,均由偏强的大陆高压所致。而热浪后期副热带高压北抬和西风带短波槽活动是热浪转换为强降水的重要环流特征。本次热浪事件引发了华北地区的干旱,而强降水事件则造成了严重洪涝,直接经济损失近千亿元。为了追踪此类灾害事件的前期信号,进一步对比了1991—2022年华北地区热浪后7 d内是否接续发生强降水事件的历史个例。结果发现,CHWHR事件之所以后期有强降水,是因为在热浪期间就存在副高偏北的特征并维持,夏季风推进至华北,并且热浪后期出现中纬度西风槽东移。此外,热浪后华北平均CAPE值是否显著下降是一个有效的预报指标。这一研究结果对于预防和减轻极端天气事件造成的灾害有一定指导意义。

     

    Abstract: Global warming has triggered increases in heat waves and heavy rainfall events, and their combined occurrences can lead to more severe impacts. Therefore, it is imperative to study the superposition of the two types of extreme event. Using temperature and precipitation data collected at meteorological stations and ERA5 and NCEP/NCAR reanalysis data as well as data released by the National Climate Center, synoptic evolution characteristics and causes of Consecutive Heat Waves and Heavy Rainfall events (CHWHR events) in North China in 2023 are analyzed. Based on multiple similar events in history, key atmospheric circulation characteristics for the occurrence of CHWHR events are discussed from a predictability perspective. We have found that this event consisted of two heatwaves and two heavy rainfall events, and lasted for 41 days. It is characterized by two heatwaves, followed by a rapid heat-humidity transition and a period of heavy rainfall with two heavy rainfall events occurring within 20 days. The duration of the two heat waves was long, and temperature exceeded the threshold in 13 out of 20 days. The heat waves are caused by the strong continental high pressure. The northward shift of the subtropical high and the activities of the short-wave trough in the westerly belt during the late stage of the heat wave are important circulation characteristics for the conversion from heat wave to heavy precipitation. The heat wave event triggered drought in North China, while the heavy rainfall event caused severe floods, resulting in direct economic losses of nearly 100 billion Chinese yuan. To identify the early signals of such disaster events, we further compare historical cases with and without heavy rainfall events within 7 days after heat waves in North China from 1991 to 2022. It is found that the reason for the heavy precipitation in the later stage of the CHWHR event is attributed to the presence and maintenance of a northward subtropical high during the heat wave with the summer monsoon advancing to North China and the mid-latitude westerly trough moving eastward in the later stage of the heat wave. In addition, whether the average CAPE value in North China significantly decreases after a heat wave is an effective forecasting indicator. Results of the present study have important implications for the prevention and mitigation of disasters caused by extreme weather events.

     

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