由於台灣地區降雨季節性差異明顯，且水庫庫容過小無法有效儲蓄水源，每逢枯水期時若降雨量持續偏低，水庫水位也會跟著驟降，而在乾旱期間往往調用農業用水以支援民生及工業用水，對農業經濟造成很大的損失，因此如何管理及分配水資源，衍然成為現今一個重要的議題。而乾旱的發生緩慢且不容易察覺，當面臨乾旱威脅時，往往已錯失最佳調配水資源的決策時機，因此，為了因應乾旱可能導致的缺水問題，若能利用相關的氣候預報資訊，預先在乾旱發生前掌握未來供水與用水情勢，並考慮不同的供水策略與補償措施，評估可行之供水情形，將是本篇研究主要目的。 選定歷史乾旱年2002年和2003年做為研究年份，利用中央氣象局發佈之季長期天氣展望資料，進行石門水庫供水評估。過程中結合預報資訊與氣象資料合成模式(WGEN)，繁衍出符合預報趨勢之未來溫度及雨量資料，再投入水文模式(GWLF)中模擬研究區域內各集水區之入流量，進一步帶入以系統動力模式軟體(Vensim)所建立的大漢溪水資源系統動力模式，以求得各標的用水每旬可能之缺水率與發生缺水之機率，評估農業用水在此缺水率下可能的休耕面積與休耕補償金額，以探討氣候預報資訊之最佳應用策略。研究結果顯示季預報有一定的可信度，在預報預測機率最大區間命中實際區間的情況下，可提早掌握乾旱發生的先機，提供決策者做出適當的水資源調適措施。 Because of significant seasonal rainfall variations and small reservoir capacity in Taiwan, agricultural water was often allocated to support the shortage of water resources for domestic and industrial water usages. As a result, compensation was applied to farm land owners and caused great loss of agricultural productions. Therefore, how to effectively manage water resources during spring drought becomes an important issue in Taiwan. Drought is not easy to detect with sufficient lead time for developing proper measures and may sustain long period before next sufficient rainfalls. Only early drought warning can be accurately issued with enough lead time, limited water resources can be reasonably allocated to support different water sectors. In this study, the historical drought events of years 2002 and 2003 were investigated with the seasonal clime outlooks, issued by the Central Weather Bureau, incorporated with the approach by combining a weather generator, a watershed hydrological model, a reservoir routing for the Shihmen Reservoir, a system dynamic model for the Dahan River water supply system. Simulation results demonstrates that seasonal climate forecast has certain credibility to provide decision-makers for applying appropriate water resource adaptation measures against spring drought.
