臺灣降雨指數 (TCCIP Taiwan Rainfall Index，簡稱TRI) 的建立，是臺灣氣象科學觀測史上，首度整合最多降雨資料所彙整成的最長雨量指數。本研究使用臺灣超過一千五百站的雨量觀測數據，包含清代觀測、氣象局綜觀測站、新收集之臺灣降雨資料庫 (來自五十一個不同來源，主要為水利署、農田水利會、臺電等之資料)，與近年氣象局自動雨量站的觀測數據，分成日與月尺度，以類似國際上著名「印度季風降雨指數」方式，提供研究者一個方便處理且具有區域整體降雨特色的雨量觀測指標，適合應用在各領域的相關研究中。本研究並以這TRI 指數做臺灣雨量長期變化的初步分析，發現過去一百多年臺灣整體年總雨量的變化，大致呈現日本時代中後期 (1920 年至戰後1960 年間) 雨量較多，1960-1990 年雨量較少，1990 年代中期後 (特別是2000 年後) 又開始明顯增加的變化。這樣的長期年代際變化趨勢，除了呈現在年總值上，也出現在極端降雨的個案發生次數上，值得政府單位參考。此外，各季節的分析則顯示，春雨與北太平洋年代際震盪有正相關，秋雨與春雨有明顯負相關，另梅雨季(五、六月) 至夏季前期 (七、八月) 的雨量年代際變化，則與全球的溫度去掉長期暖化趨勢後的變動有關。

A TCCIP Taiwan Rainfall Index (hereafter TRI), the longest rainfall index in the Taiwan meteorological history, is constructed in this study. The TRI is based on the long-term rich data from observational stations in Taiwan. More than 1,500 stations are used including observations during the Ching dynasty, the conventional weather stations, the newly acquired Taiwan Rainfall Data (from 51 different sources,including the major contributors as the Water Resources Agency, Irrigation Associations and Taiwan Power Company), and Central Weather Bureau’s automatic rainfall station data. The TRIs have daily and monthly versions. The longest index starts from 1885 and ends in 2010. Similar to the well-known“All India Monsoon Rainfall Index”, the TRIs represent the variations of Taiwan rainfalls and can be used for many different research purposes.Using the TRI, the long-term rainfall variability in Taiwan is studied. Results show that there were more rain in 1920-1960s, less rain in 1960-1990s, and more rain again aft r mid-1990s (especially after 2000) with respect to the long-term climatology. These decadal variations are found in both yearly sum of rainfall amount and the number of extreme events. This study further analyzes the decadal to inter-decadal variations of rainfalls in each natural season. Results show that (1) the spring rain is highly correlated to the Pacific Decadal Oscillation; (2) the spring rain and autumn rain are negatively correlated; and (3) the decadal variations of rainfalls between Mei-yu (May-June) and early summer season (July-August) are related to the global temperature change in which the long-term warming trend is removed.