1013 Typhoon Season Extreme Rain Characteristics of Taiwan

Wednesday, 10 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Alex Henny, SUNY, Albany, NY; and M. E. Howarth, C. D. Thorncroft, H. H. Hsu, and L. F. Bosart

Extreme precipitation has widely been found to increase more quickly than total precipitation in global warming scenarios. With its high mountain range and its location at the cusp of the tropics, Taiwan is a place where both frontal systems and typhoons produce heavy rainfall, and where extremes are tightly bound to orography. As such, it provides a natural testing ground for determining the importance of convection, of typhoons, and of synoptic disturbances for extreme rainfall. One goal of the NSF U.S. – Taiwan PIRE (Partnerships for International Research and Education) project is to assess the causes and variability of trends in extreme rainfall in Taiwan. In this initial work, we lay the foundation for this task by using 1 km gridded rainfall data from the Taiwan Climate Change Projection and Information Platform Project (TCCIP) to calculate trends in typhoon-season extreme rainfall over Taiwan, and averaging NCEP reanalysis data over the extreme days to get a composite of the “average” extreme storm at different points of the island. Using typhoon track data, we separate the extreme events into typhoon and non-typhoon classes and more specific subsets, and again use NCEP data to compute trends in storm characteristics.
Rainfall extremes are largest over the southern and central portion of the Central Mountain Range (CMR), on the western slopes. Large positive seasonal extreme rainfall trends of up to ~10 mm/yr prevail over the southern and central mountain slopes, with a small ~3 mm/yr negative-trend region on the central eastern slopes. Extreme storms in the positive and negative-trend regions have different typhoon-related signatures: on average, southern extremes occur with typhoons tracking over the middle of the island, whereas central eastern extremes occur with typhoons tracking over the southern tip of the island. The more northern track brings southwesterly monsoon winds up the south- and west-facing slopes; likewise, a southern track generates ascent on the eastern slopes. Extreme rain may also occur long before or after the passage of the typhoon, aided by monsoon flow interacting with the mountains. Trends indicate that both classes of storms are increasing in strength, with the southern track potentially moving northward.
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