| 摘要: | 本研究使用中央氣象局1950年至2010年，共計61年之逐日累積雨量資料，將其轉換成5個世界氣象組織(World Meteorology Organization, WMO)定義之氣候變遷指數，分別為簡易逐日降雨強度(SDII)、大雨日數(R50)、連續五日累積雨量(R5d)、第95百分閾值降水量百分比(R95p)等與降水強度、級數相關之指數，以及與乾旱相關之連續乾燥日數CDD，期以瞭解臺灣地區降雨量在全年及不同季節(春季、梅雨季、夏季、颱風季、秋季及冬季)的趨勢變化特性。首先將逐日降水資料分為兩個時期(1950-79和1980-2010)，比較其機率密度函數(PDFs)之差異。SDII依強度大小略分為三類：小雨、中雨和大雨。後期中雨和大雨的發生頻率有增加的現象，小雨發生頻率卻為減少的情況，其他降水相關指數也都有類似的情形，但CDD在後期長日數之發生頻率有增加的現象，說明臺灣地區氣候趨於乾溼分明。 再以無母數趨勢檢定方法分析各項指數在不同季節的空間分布變化趨勢及其顯著性。除了R50之外，其他各項指數在夏季及颱風季全區都有上升的趨勢，場顯著水準多在5%以上；而在冬季及春季則有顯著的南北差異，南部地區CDD呈現上升的趨勢且SDII為下降的趨勢，北部地區則為反相。顯示南部地區在乾季缺水情況日益嚴重。 最後使用30年變動序列(1950–79, 1951-80,. . . , 1980–2010)探討各站不同季節趨勢變化是否穩定。結果顯示，CDD在南(北)臺灣冬季的變動序列為下降(上升)的趨勢，說明南部在冬春季的乾旱現象雖日益嚴重但趨於穩定；而SDII在全年及夏季的變動序列有上升的趨勢，說明降水強度不僅逐年增強且變化幅度更劇烈。 In this research, trends of five climate change indices related to extreme precipitation events in Taiwan are investigated using daily observational records of conventional surface stations from 1950 to 2010. Four indices [simple daily intensity index (SDII), total number of day with precipitation ≥50 mm (R50), annual maximum consecutive 5-day precipitation amount (R5d), and the fraction of annual total precipitation from events exceeding the 1961–90 95th percentile (R95p)] describe the intensity (SDII), frequency (R25), and magnitude (R5d and R95p) of precipitation extremes, and the fifth index [consecutive dry days (CDD)] describes drought conditions. The annual probability density functions (PDFs) of precipitation indices for two epochs (i.e., 1950–80 and 1981–2010) are analyzed. The SDII is then roughly classified into three types: light, moderate, and high intensity. Since the 1980s, there has been a change in the types of precipitation intensity, resulting in more frequent moderate and heavy precipitation and less frequent light precipitation intensity. The other three precipitation-related indices (R25, R5d, and R95p) demonstrate a shift toward the right of the PDF over time, suggesting shorter annual number of days with intense precipitation and smaller consecutive 5-day precipitation amounts and smaller fraction of annual precipitation due to events exceeding the 1961–90 95th percentile from the first to the second epoch. A nonparametric trend analysis is then performed for the entire period and six seasons, namely, spring, meiyu, summer, typhoon, autumn and winter. Long-term upward trends are evident for all five indices except R50. Southeastern Taiwan are dominated by upward trends of CDD (longer consecutive dry days)and downward trends of SDII (less intense precipitation), in particular during spring and winter season. To investigate whether the trends are stable throughout the time, the derivatives of trends for each of the 30-yr running series are calculated (e.g., 1950–79, 1951–80, . . . , 1980–2010) for four precipitation-related indices at each station. For northern (southern) Taiwan, positive (negative) derivatives prevail for CDD in the presence of long term negative (positive) trends in the spring season, suggestive of a phase change in precipitation extremes and such extremes showing an upswing (downswing) recently. For Taiwan, there is also an indication of phase reversal over the last 60 year, with negative derivatives occurring in the presence of the background positive trends. |
