2023年华北热浪-强降雨水连续极端事件的成因及可预测性分析

Causes and predictability of continuous extreme events of heat wave and heavy rainfall in North China in 2023

中文关键词:  连续极端事件  热浪 强降水  华北 大陆高压  副热带高压 旱涝急转

英文关键词:Continuous  extreme events, heatwaves, heavy  rainfall, North  China, continental  high pressure, subtropical  high pressure, droughts  and floods  sudden turn

中文摘要:

      全球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。本文重点从天气尺度分析了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天。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天内出现2次强降水事件。就热浪事件而言，2次热浪持续时间长，20天内13天超过阈值，均由于偏强的大陆高压所致。而热浪结束后2次强降水事件的成因较复杂，第一次是西风槽带来的冷空气与西北太平洋副热带高压（后简称“西太副高”）西北侧暖湿气流交汇所致，而第二次强降水则主要是双台风共同作用引起。本次热浪事件引发了华北地区的干旱，而强降水事件则引发了严重洪涝，经济损失近千亿元。为了追踪此类灾害事件的前期信号，我们进一步对比了1991~2022年华北地区热浪后7天内是否接续发生强降水事件的历史个例。结果发现，CHWHR事件能否发生的关键环流因子是西太副高是否异常北抬中纬度西风气流是否平直、是否存在明显高压脊和夏季风能否顺利推进至华北。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。

英文摘要:

      Global warming has triggered a rise in heat waves and heavy rainfall events, and their combined occurrence can lead to more severe impacts. This article focuses on analyzing the evolution characteristics and causes of the Consecutive Heat Wave and Heavy Rainfall events (CHWHR events) (CHWHR) events in the North China region in 2023 from a weather scale perspective. Based on multiple similar event cases in history, the key atmospheric circulation characteristics for the occurrence of CHWHR events are discussed from a predictability perspective. We found that this event consisted of three heatwaves and three heavy rainfall events, and lasted for 41 days. Its characteristic was that there were three heatwaves first, followed by a rapid transition from heat to humidity and entering a period of heavy rainfall, with three heavy rainfall events occurring within 20 days. In heat wave events, the duration of the three heat waves was long, with 14 days exceeding the threshold within 20 days, all due to the strong continental high pressure. The causes behind the three heavy rainfall events following the heat wave"s end were more complex. The first two were caused by the cold air brought by the westerly trough intersecting with the warm and humid air flow on the northwest side of the Northwestern Pacific Subtropical High (WPSH), while the third heavy rainfall was mainly caused by the combined action of two typhoons. We found that this event consisted of two heatwaves and two heavy rainfall events, and lasted for 41 days. Its characteristic was that there were two heatwaves first, followed by a rapid transition from heat to humidity and entering a period of heavy rainfall, with two heavy rainfall events occurring within 20 days. In heat wave events, the duration of the two heat waves was long, with 13 days exceeding the threshold within 20 days, all due to the strong continental high pressure. The causes behind the two heavy rainfall events following the heat wave"s end were more complex. The first one were caused by the cold air brought by the westerly trough intersecting with the warm and humid air flow on the northwest side of the Northwestern Pacific Subtropical High (WPSH), while the second heavy rainfall was mainly caused by the combined action of two typhoons. The heat wave event triggered drought in North China, while the heavy rainfall event triggered severe flooding, resulting in economic losses of nearly 100 billion yuan. In order to track the early signals of such disaster events, we further compared historical cases of whether heavy rainfall events continued to occur within 7 days after heat waves in North China from 1991 to 2022. We found that the key circulation factors determining whether the CHWHR event can occur are whether the WPSH abnormally rises northward and whether the summer monsoon advances abnormally fast. , whether the mid latitude westerly airflow is flat, whether there is a significant high-pressure ridge, and whether the summer monsoon can smoothly advance to North China. In addition, whether the average CAPE value in North China significantly decreases after a heat wave is an effective forecasting indicator. This research result has certain guiding significance for preventing and mitigating disasters caused by extreme weather events.