Characteristics and causes of Taiwan's extreme rainfall in 2022 January and February

Abstract

Over the past 40 years (1982–2021), the January and February (JF) rainfall in Taiwan has shown a clear decreasing trend. However, in 2022, the JF rainfall suddenly climbed to the third-highest value ever recorded in Taiwan. This study aims to explore the characteristics and causes of this unique event. Our results show that the significant increase in JF 2022 rainfall is contributed by both an increase in rainfall occurrence frequency and an increase in rainfall intensity. Further analysis shows that most of the JF 2022 rainfall is contributed by the rainy systems propagating from South China or the north of South China Sea to Taiwan but without the frontal structure, which is different from the general concept that JF rainfall is dominated by winter monsoon circulation-induced orographic rainfall and frontal rainfall. As a result, southern Taiwan experienced more than a 130% increase in JF 2022 rainfall compared to the JF climate mean. Possible physical explanations for the increase in JF 2022 rainfall can be attributed to the enhanced winter background circulation, which featured an enhanced regional northeasterly wind at 925 hPa coupled with an enhanced southwesterly wind transporting moisture at 700 hPa covering the domain of (10°-30°N, 100°-120°E). Consequently, an active convection zone extending from the southeastern Bay of Bengal to Taiwan was revealed in JF 2022 to result in the extreme rainfall in Taiwan. Further analysis also indicates that the relationship between the Taiwan JF rainfall and the tropical sea surface temperature has changed since 2002.