近幾十年來，全球平均溫度逐年增加，改變了整個大氣環流的正常機制，造成全球氣候變遷事件頻傳。台灣地處東亞季風區帶，因此各季節的降雨量亦深受全球氣候變遷的影響。台灣各季節的降雨趨勢、週期如何，將是本研究探討的重點。本研究採用中央氣象局台北、台中、台南、恆春、台東、花蓮、澎湖、及彭佳嶼八站自設站到2004年的降雨量資料，利用時間序列簡單線性迴歸模型分析近百年和近40多年的春季、夏季、秋季、冬季、梅雨季和颱風季之趨勢。結果顯示，在近百年的降雨趨勢中，大部分的季節裡，北部、東北部的雨量在增加，而西部與南部則多在減少中；在近40多年的降雨趨勢中，仍是北部的降雨量為增加趨勢，台南、澎湖及花蓮的降雨量則為減少趨勢。
在各季節降雨週期方面，台灣各季節降雨量最主要的週期為2~4年，且大部份各測站各季節降雨量週期顯著性達到95%，少部分為90%顯著性。次要週期是5~8年、9~12年的週期。
在降雨量與週期之相關性方面，台南春季和澎湖春季、台中梅雨季降雨量與El Niño具低度正相關性；恆春夏季和颱風季降雨量與El Niño呈現低度負相關性。花蓮夏季和颱風季降雨量、台南夏季、台中梅雨季降雨量與SOI呈現低度負相關性。台北秋季和恆春梅雨季降雨量與QBO呈現中度正相關性，恆春颱風季降雨量卻與QBO呈現中度負相關性。
The global average temperature is increasing for the past decades by the globally climatic change. The precipitation of Taiwan in each season is probably affected. The purpose of this study is to investigate the trend and periodicities of seasonal precipitation in Taiwan. The simple linear regression model was used to analyze the trend of precipitation of eight representative stations which are Taipei, Taichung, Tainan, Hengchun, Hualien, Taitung, Penghu, and Pengchiayu, distributed evenly around Taiwan. The results reveal that the precipitation in summer, fall, Meiyu, and typhoon season has obviously increasing trends in northern Taiwan and decreasing trends in southern Taiwan.
The main periodicity of precipitation is 2~4year with 95% significance is found in each season in most Taiwan. Secondly, the 5~8year and 9~12year periodicities are also found in most stations.
The precipitation in Tainan and Penghu in spring, in Taichung in Meiyu has low positive relation to El Niño. The precipitation in Hengchun in summer and in typhoon has low negative relation to El Niño. The precipitation in Hualien in summer and in typhoon, in Tainan in summer, and in Taichung in Meiyu has low negative relation to SOI. The precipitation in Taipei in fall and in Hengchun in Meiyu has median positive relation to QBO. However, the relation between the precipitation in Hengchun in typhoon and QBO is median and negative.
