本研究將針對蘭陽溪流，運用土地利用現況資料與SRES(Special Report on Emissions Scenarios)氣候預設情境，探討未來氣候變遷對GWLF（Generalized Watershed Loading Function）水文模式模擬流量之影響。並且修正GWLF水文模式，使其模擬更加準確。首先修改GWLF水文模式中，有關蒸發散的部分，並且探討修改後是否更加符合真實的蒸發散情形。氣候變遷方面，使用歷史氣象資料，與SRES預設情境氣象資料輸入GWLF模式所模擬出未來短、中、長期之流量與，評估氣候變遷對其可能造成之影響與衝擊。分析結果顯示，修改後所得之GWLF模式可以更加準確模擬蒸發散情形。未來的降雨量、流量在氣候變遷影響下呈現增加的趨勢，但在枯水期相對於現況為減少趨勢且顯著於豐水期，未來降雨量多集中在豐水期顯示降雨分布不均的情況更為嚴重，顯示未來水資源的利用勢必更加困難。 This research focuses on the influence of streamflow, simulated by GWLF (Generalized Watershed Loading Function) model, under climate change with land use data and SRES (Special Report on Emissions Scenarios) climate scenarios in Lanyang watershed. A modified evapotranspiration part of GWLF was suggested to enable the model to simulate the real nature. Historical meteoric data and SRES climate scenarios was used to simulate the future short-term, med-term and long-term change of streamflow. The result indicated that the modified GWLF could estimate the evapotranspiration more accurate. Rainfall and stream flow were trended to increase under climate change influence in the future, but the trend of decrease in streamflow in dry season was observed to be more serious than the trend of increase in streamflow in wet season. In order words, rainfall concentrates on wet season but the temporal distribution becomes less evenness in the future. As a result, water resource management will face challenge in the future.