近年來，台灣地區氣候變動異常，降雨量極端不穩定，而文獻亦指出過去一百年全球溫度有上升之趨勢，此種雨量與氣溫之改變可能導致台灣地區因氣候異常變動而造成降雨量不足之乾旱現象，尤其是降雨與氣候型態的改變，導致水源短缺、可利用水分配與管理不易，乾旱現象將愈漸嚴重。
　　本研究首先建立台灣南部地區各雨量站之標準化降雨指標(Standardized Precipitation Index)，並對照歷史乾旱紀錄，分析SPI之時間及空間特性。再使用Cumulative Deviations檢定法、Mann-Whitney-Pettitt檢定法與Kruskal-Wallis檢定法，檢定近百年長期雨量及氣象資料(年平均氣溫與歷年侵台颱風紀錄)之變化趨勢，對乾旱發生頻率及延時之影響。更進一步利用區域標準化降雨指標與歷史乾旱現象之關係，由乾旱與非乾旱群集，建立農業乾旱監測模式。
　　本研究演算之各空間等值圖，可驗證SPI在空間上乾旱監測能力，發現SPI可適切反應區域上之乾旱發生情況。從長期雨量統計分析，發現南部地區之乾旱現象正漸趨嚴重中，南部地區之年降雨量發生改變點的位置一致，大約在1950－1960年代左右，且有明顯減少之趨勢，而影響南部地區降雨量甚鉅之颱風路徑3，在1956年後顯著地減少，可能為南部地區颱風季降雨量短缺、乾旱發生頻率增加之原因。大約在1956年以後，中度乾旱、嚴重乾旱、極端乾旱發生頻率都有明顯增加之現象，而乾旱之平均延時亦有拉長之現象。由乾旱與非乾旱群集中，發現乾旱時期與非乾旱時期各有其不同特性，且嘉南地區隔年一月SPI6與SPI9平均值判別乾旱年與非乾旱年之各月份正確率最高(91％)。

　　The abnormal climate and the significant change of rainfall happen recently in Taiwan and many references also indicated that the past 100-year temperature records were increasing. The variations of rainfall and temperature may cause the change of drought characteristic. The variations of rainfall and climate could lead to the decrease of water availability, the difficulty of water management, and severer drought phenomenon.
　　This study establishes the Standardized Precipitation Index (SPI) based on the historical records of 30 rainfall stations in Southern Taiwan. Meanwhile, information on historical drought events has been collected to analyze spatial and temporal variability of the SPI. Three statistical tests, Cumulative Deviations test, Mann-Whitney-Pettitt test and Kruskal-Wallis test, are adopted to estimate the variation and tendency of these long-term historical rainfall and meteorological series. Then, the impacts of drought frequency and duration are analyzed from the long term precipitation and meteorological variation. Moreover, the relationship between regional SPI and historical drought characteristic are employed to set up an agricultural drought monitor from two groups of drought and non-drought events.
　　Each spatial variation figure of the SPI can verify the monitor ability and reveals that SPI can reasonably response the drought condition. Besides, these annual rainfall series in Southern Taiwan have similar change points, approximately from 1950 to 1960 and have a significantly downward tendency. The average typhoon hitting numbers of route three which influenced rainfall very much in Southern Taiwan significantly reduced after 1956. The numbers of medium, severe and extremely severe droughts significantly increased and the average duration of drought also became longer about after 1956. Results also show that drought and non-drought periods have different traits. Using the combination of SPI6 and SPI9 to judge whether the drought event occurs in Chianan Area, the accuracy in January in the following year is the highest (91%).

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