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

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.