本研究以大氣環流的差異，分析臺灣長期以來的颱風活動變化。首先統計1950至2014年臺灣颱風季各月份的颱風日數，並以環流差異解釋其颱風日數變化的原因。在7至9月時，強駛流區域若正對臺灣及琉球群島方向，颱風容易受該環流導引朝臺灣移動，因此侵臺颱風日數多；反之，當強駛流區域遠離臺灣，而是朝南海或日本南方海域方向時，颱風不易接近臺灣，因此侵臺颱風日數少。在6月與10月，臺灣的氣候環境條件並不利於颱風接近，若強駛流區導引颱風向西進入南海或北轉朝東北亞地區，則臺灣不受颱風影響，多造成無侵臺颱風的狀況。
百年以來侵臺颱風個數與日數，呈現先逐漸減少，於20世紀中期再開始增加的趨勢。年平均單一颱風的影響時間同樣先逐漸減少，於1960年代後再增加並持續至今。從駛流場發現，其原因為臺灣附近的東風先後歷經20世紀中期的增強，至近代又減弱的變化，進而使早年颱風移動速度先加快，於近年來卻減慢。
在降水方面，百年以來侵臺颱風降雨在最近20年間大幅增加。年平均單一颱風降雨呈現先減少，自1990年代起快速增加的趨勢，而且近幾年每個颱風個案的總降雨量明顯較過去來的高。其原因推論為近年來臺灣附近的東風減弱使颱風移動速度減慢，增加停留在臺灣的時間，造成每個颱風對臺灣的平均降雨增加。

This study analyzes the long-term changes of typhoon activities in Taiwan based on the differences of large scale circulation. The circulation variation is analyzed to interpret the changes of typhoon affecting days during the typhoon season in Taiwan (June-October) from 1950 to 2014. From July to September, typhoons tend to approach Taiwan when strong steering flows extend towards Taiwan and Ryukyu Islands, leading to more typhoon affecting days. In contrast, when the strong steering flows move far away from Taiwan and instead extend towards South China Sea or south of Japan, typhoon activities near Taiwan significantly reduce and that results in less affecting days. In June and October, the large scale environmental condition around Taiwan does not benefit typhoons to approach. For these days without typhoons affecting, typhoons are guided by different steering flow branches to move westward directly into South China Sea or recurve northward to Northeast Asia.
In the past hundred years, the total amounts of the typhoon affecting Taiwan and typhoon affecting days show interdecadal variations, with a decreasing trend before the mid-20th century but an increasing tendency after that. The annual averaged typhoon affecting days also exhibit a decreasing trend before the 1960s and an increasing tendency after that. An explanation for those findings is that the easterly steering flows around Taiwan strengthened in the mid-20th century but weakened in recent years, which would influence the typhoon translation speed.
The typhoon-related rainfall in Taiwan has been increasing significantly in the past 20 years. The annual averaged typhoon rainfall exhibits a decreasing trend before the 1990s and a rapidly increasing trend after that. In addition, the total rainfall from each typhoon in recent years is also on the rise. Results for those phenomena suggest that the weakening of the typhoon translation speed related to the change of the easterly steering flows leads to the increasing trend of averaged typhoon rainfall in Taiwan.

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