Compound Disasters Intensify in South Korea: Heatwaves Follow Heavy Rains

South Korea is facing a stark increase in "compound disasters," characterized by the rapid succession of different extreme weather events such as heavy rainfall followed by intense heatwaves. A recent analysis reveals that the intensity of these combined climate phenomena has tripled over the past four years when compared to the preceding three decades.

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) analyzed data from June to September between 1991-2020 and the more recent period of 2021-2024. They used a "Compound Intensity Index" (CI28), which combines extreme precipitation and maximum temperatures over a 28-day period. The median value of this index rose from 0.55 in the earlier period to 1.65 in the recent four years, indicating a significant overall increase in the severity of compound disasters.

The study also highlighted a dramatic rise in the frequency of extreme compound disaster days. When using the top 1% of CI28 values from the past 30 years as a benchmark, the number of such extreme days has surged from an average of 1.1 days per year to 5.2 days per year, an almost fivefold increase. This means that events of the most extreme compound risk, which previously occurred about once a year, are now happening more than five times annually.

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The intensity of compound disasters has increased about threefold in the last four years compared to the past 30 years.

This trend is not uniform across the country, with regions like North Chungcheong, Gangwon, and Jeju experiencing more than double the compound disaster intensity in the last four years compared to the previous 30-year period. The phenomenon is attributed to atmospheric circulation patterns in the East Asian monsoon climate, where the same systems can rapidly shift from causing heavy rainfall to generating intense heat.

Scientists emphasize that viewing heavy rain and heatwaves as isolated events is insufficient for understanding the risks. As global warming progresses, the rapid transitions between these extreme conditions are likely to intensify. Therefore, a response system that considers the potential for sequential and simultaneous occurrences, rather than just single disaster types, is crucial.

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The number of days with extreme compound disasters has also significantly increased. The most extreme top 1% level compound disasters increased from an average of 1.1 days per year to 5.2 days, a 4.8-fold increase.