Changes in extreme precipitation in Taiwan's Mei-yu season

High-resolution Taiwan Climate Change Projection Information and Adaptation Knowledge Platform (TCCIP) gridded precipitation data are used to characterize days in the Mei-yu season with the most extreme precipitation (EP). These EP days are grouped into weather types based on the presence of features such as tropical cyclones (TCs) and atmospheric rivers (ARs), then analyzed from the perspective of weather type frequency and synoptic changes. During the 1979-2019 period, EP days associated with ARs were associated with significant increasing trends in season-total precipitation. These AR-related precipitation increases are due to four events in 2005, 2006, 2012, and 2017 which had long duration and unusually intense precipitation, and which were anomalous even within the longer 1960-2019 time period. Meanwhile, TC-related EP days contribute less precipitation than they did in the 1980s due to decreased frequency of TCs on EP days and in the Mei-yu season climatology. Over the 1979-2019 period, the AR-related and TC-related trends combine to produce EP increases in western Taiwan and decreases in eastern Taiwan. Mei-yu season southwesterly integrated vapor transport (IVT), wind speed, and specific humidity have all increased in association with these extreme events. Low-level winds appear to the primary factor influencing the IVT increase, with increased moisture also contributing. The wind trends are consistent with climatological pressure increases south of Taiwan and decreases over the East Asian landmass, which facilitate a strengthened circulation in a corridor extending from the southern China coastline over Taiwan during this season.

Automated summary

The study utilizes Taiwan Climate Change Projection Information and Adaptation Knowledge Platform (TCCIP) gridded precipitation data to investigate extreme precipitation (EP) days during the Mei-yu season. The EP days are classified into weather types based on the presence of tropical cyclones (TCs) and atmospheric rivers (ARs), and their frequency and synoptic changes are analyzed. The results show that EP days associated with ARs exhibit a significant increasing trend in season-total precipitation, while TC-related EP days contribute less precipitation due to decreased TC frequency. The combined trends of AR-related and TC-related events lead to EP increases in western Taiwan and decreases in eastern Taiwan. Southwesterly integrated vapor transport (IVT), wind speed, and specific humidity during the Mei-yu season have all increased, with low-level winds and increased moisture being the primary factors driving the IVT increase.