The Climatology of Taiwan extreme rainfall events and the attributions

Abstract:

Taiwan is located in the East-Asian monsoon region with average 2,500mm annual precipitation. Most significant Meteorological disasters are related to extreme precipitation which is associated with a complex terrain. Therefore, the long-term trends or climate variations in precipitation due to climate change are our major concern. We studied the climatology of extreme rainfall (ER, 95^thpercentile) events in Taiwan using hourly precipitation data form 21 surface stations during 1960-2014. ER contributes about 40% of the total rain amount. It was found that approximately 68% of ER is related to typhoon (TY) and 22% associated with the Mei-Yu (MY) frontal system.

The total ER amount annual variation is strongly related to TY, with correlation coefficient of 0.89 for rainfall amount and 0.86 for frequency. There is a significant increasing trend of TY-ER in past 55 years, but also has large variations over the annual and decadal time scales. The inter-annual variation of astounding extreme rainfall (AER, 99.9^thpercentile) is increased significantly, especially in the past 15 years. It implies that the increasing of AER rainfall amount majorly caused by the increasing of frequency instead of average rain intensity of TY-AER. The MY-ER events are also highly correlated with the frontal system. The correlation is 0.84 for the rainfall amount and 0.83 of the frequency with the frontal days. There are also strong inter-annual variations of MY-ER, but the long-term trends are not as significant as TY-ER. The variation of frontal system number is another parameter may impact the MY-ER. The observational frontal system numbers had positive correlation with the MY-ER.

The attribution of Taiwan TY-ER changes was debated in the research community. In general, the public acceptance of Taiwan extreme precipitation events is affected by multi-scale systems. According to observational data, the increasing of TY-ER amount is 37 % (48% )in Taiwan and some resent studies (Wang et al. 2015 and Chen et al. 2015) indicates the 10-15%(25%) of the TY rainfall (ER) increasing was contributed by GHG effect. In the other words, the impact of climate change may be obscured by the terrain effects. We also indicate the climate scale variations may also play an important role for the large-scale water vapor supply or the track of tropical cyclones.