於氣候變遷影響下，全球暖化加劇且極端之水文事件增加，乾旱逐漸成為研究學者、政府單位或是一般大眾所密切關注之議題。近年來氣候異常，導致臺灣未來降雨量將呈現豐水期愈豐、枯水期愈枯之趨勢，增加乾旱發生頻率、嚴重程度提升以及乾旱期距延長，容易造成水資源利用與調配更加艱難。
本研究採用降雨量與水庫蓄水量作為乾旱影響因子，發展石門水庫適用之乾旱預警指標，參考世界氣象組織於乾旱等級劃分之作法，分析乾旱預警指標與歷史事件之關係。進一步應用區別分析作為分類方法，以現況乾旱預警指標、未來乾旱預警指標以及未來水情燈號之關係建立乾旱預警模式，最後採用2014至2015年乾旱事件作為案例模擬。期望在乾旱來臨前，藉由乾旱預警模式提供決策者相關資訊，儘早啟動超前布署，透過加強灌溉節水管理與啟動備援水源設施等作為，能夠延長水庫供水日數，有助於紓緩乾旱對社會經濟之衝擊，全面提升抗旱韌性。
將乾旱預警指標與歷史事件進行分析，發現標準化降雨量指標(Standardized Precipitation Index)與標準化水庫蓄水量指標(Standardized Reservoir Storage Index)皆能明確地反映歷史乾旱事件，確立乾旱預警指標於歷史乾旱事件具有一定之掌握度後，應用於乾旱預警模式之建置。於乾旱預警模式中，最佳之現況乾旱預警指標組合為SPI1與SRSI1，並導入未來氣象條件(未來乾旱預警指標)進行未來燈號判別，結果顯示：加入未來乾旱預警指標有助於提高未來水情燈號之準確率，且不論是在率定年或驗證年之乾旱預警模式，對於未來燈號判別皆為枯水期間表現較豐水期間佳。

This study aims to develop a drought early warning model based on the standardized drought indices (SDI) for the water resources system of Shihmen Reservoir in northern Taiwan. Different hydrological variables (e.g., rainfall, reservoir inflow and storage) were used as the basis of SDI to characterize and monitor drought condition for water resources system. The SDI calculated by the historical rainfalls, reservoir inflows and storages were analyzed. It is found that the value of SDI can clearly reflect the situations of historical drought events. Further, the discriminant analysis was adopted to establish the drought early warning model based on the relationship among current SDI, future SDI and future regime lights. In the drought early warning model, the best combination of drought warning indices include current SDI (i.e., SPI1, SRSI1) and future SDI (i.e., SPI1 and SPI3) for predicting the future regime lights. The results show that adding future SDI can improve the prediction accuracy of future regime lights. For both the calibration period (1958－1997) and the verification period (1998－2017), the drought early warning model reveals satisfactory performance for predicting future regime lights. The prediction performances during the dry season are better than those during the wet season.

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