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Chih-Pei Chang

2012-09-19
10:35:00 - 11:25:00

101 , Mathematics Research Center Building (ori. New Math. Bldg.)

Interpretations of extreme rainfall trends in the Asian monsoon regions are complicated by tropical cyclones (TCs) from tropical oceans, whose rainfall trend may be different from the local monsoon (non-TC) rain. In the last half century the trends over the China summer monsoon region have been distorted by western North Pacific typhoons with the TC-related extreme rainfall trend smaller than monsoon-related extreme rainfall. The net impact underestimates the increasing trend in monsoon extreme rainfall over most areas. The largest underestimate occurs in Hainan Island, while an opposite case occurs in Taiwan whose extreme rainfall trend is hugely inflated by local increases in TC rainfall in the last decade. The increases are due to slowly-moving modest TCs and small variations of their tracks relative to the high mountains. If the terrain factors are taken into account, the apparent large increase in TC-related rainfall before and after landfall disappears. The remaining increase due to stronger TC - monsoon interactions becomes apparent only after the typhoon center exits Taiwan; and the preliminary analysis of a century-long record suggests this may reflect multidecadal variations. These regional and local variations also highlight the importance of considering different mechanisms of rainfall systems in order to differentiate regional and global drivers in the attribution of extreme rainfall trends.

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