本研究以臺北市士林區坪頂古圳灌區為研究對象，探討氣候變遷下耕種策略調整對緩解灌溉缺水之效益。
坪頂古圳灌區屬川流式引水系統，主要仰賴上游溪流及既有圳路供水，且缺乏大型蓄水設施，因此灌溉供水能力易受降雨變化與枯水期低流量影響。
本研究結合臺灣氣候變遷推估資訊與調適知識平台（TCCIP）AR6氣候推估資料、GWLF水文概念、HEC-RAS圳路最大通水能力分析及Vensim系統動力學模式，建立逐日灌溉供需模擬架構。
本研究將灌區劃分為七個田區，整合水源流量、圳路限制、輸水損失、田區供排水路徑及灌溉需水量，逐日計算各田區可供水量與灌溉需水量之差異。當供需平衡結果小於零時判定為缺水日，
並統計缺水日數、最大連續缺水日數、缺水量及年度缺水頻率；當年度缺水頻率達0.30以上時，定義該年度為嚴重灌溉缺水年，並計算各田區之嚴重灌溉缺水年發生機率 P及重現期距 T。
結果顯示，未來氣候情境下各田區之灌溉缺水風險具有明顯差異，其中SSP3-7.0情境下田區4、田區5及田區6為主要關注田區。田區4主要受到有效灌溉面積較大及灌溉需水量較高影響；
田區5之較高風險與其位於登峰圳供水路徑下游、登峰圳分流比例及上游取水時序有關；田區6則受到較高需水負荷、登峰圳分流及內雙溪補充條件共同影響。
本研究進一步以SSP3-7.0未調適情境下各田區之嚴重灌溉缺水年發生機率 P作為風險分級依據，建立S1風險導向差異化面積調整、S2等總量等比例面積調整及S3馬鈴薯轉作情境。結果顯示，
在全區有效灌溉面積及灌溉需水量均減少25.48%的相同條件下，S1使田區4、田區5及田區6皆由第4級降為第2級，S2則使三個田區由第4級降為第3級。S3-30在不減少有效灌溉面積之條件下，
將目標田區30%的原概化作物種植面積轉為馬鈴薯，使田區4及田區6由第4級降為第3級，田區5則維持第4級。研究成果可作為傳統川流式灌區進行需水端調適與風險導向資源配置之參考。;
This study investigates the effectiveness of cropping strategy adjustments in mitigating irrigation water shortages under climate change in the Pingding Canal Irrigation District，
located in Shilin District， Taipei City. The irrigation district is a run-of-river diversion system that relies primarily on upstream streamflow and existing irrigation canals.
Owing to the absence of large-scale water storage facilities， its irrigation water supply is susceptible to changes in rainfall and low-flow conditions during the dry season.
This study integrates climate projection data from the Taiwan Climate Change Projection Information and Adaptation Knowledge Platform (TCCIP) under the Sixth Assessment Report (AR6)，
the hydrological concepts of the Generalized Watershed Loading Functions (GWLF) model， an analysis of the maximum conveyance capacities of irrigation canals using HEC-RAS，
and a system dynamics model developed in Vensim to establish a daily irrigation water supply–demand simulation framework.
The irrigation district was divided into seven fields. Water-source discharge， canal conveyance constraints， conveyance losses， field-level water supply and drainage pathways，
and irrigation water requirements were incorporated to calculate the daily difference between available water supply and irrigation demand for each field.
A day was defined as a water-shortage day when the water balance was negative. The number of water-shortage days， maximum consecutive water-shortage days，
water-shortage volume， and annual water-shortage frequency were subsequently calculated. A year with an annual water-shortage frequency of 0.30 or greater was defined as a severe
irrigation water-shortage year. The occurrence probability ?
