资源环境科技发展态势分析平台

Taiwan's most significant natural hazards are caused by hydrological extremes resulting from excessive precipitation. The threat of extreme precipitation is posed by several different types of weather patterns that affect Taiwan. This study examined the bi-decadal changes in rainfall by defining an extreme precipitation occurrence (EPO) for a range of event durations from 1 to 24 hr. Three major weather types affecting EPO in Taiwan were identified from 1993 to 2015: the front type consisting of either a frontal zone or convective systems developing with an apparent Meiyu cloudband, diurnal rainfall events when no apparent synoptic features are present, and a tropical cyclone (TC) type according to the maximum sustained wind radius of a TC. Results show that TC-type events have the greatest overall contribution to EPO at longer (>6 hr) durations. Diurnal/afternoon convection events contribute most to the shorter (<3 hr) duration EPO, while frontal/Meiyu systems prevail in the medium (3-6 hr) duration. EPO of almost all durations have experienced an increase, with the 3- and 12-hr EPO having increased by 4.6 days each over the 23 years. However, apparent decadal-scale variability exists in these EPO associated with the decreasing tendency of EPO after the mid-2000s, particularly the longer duration (>6 hr) EPO associated with the TC-type events in summer. The distinction between EPO trends for the entire island of Taiwan and for the Taipei metropolitan area alone (northern Taiwan, population of 7 million) were compared, and an intriguing interannual variation is reported in the TC-type EPO associated with the TC season 1 year to a year and half just before an El Nino-Southern Oscillation event. The analysis here provides refined statistical distributions of extreme rainfall, and these can contribute to the revision of governmental definitions for weather disasters that are used in mitigation and response strategies.