圖書典藏及影音數位平台

台灣降雨量分布不均，且近年來受氣候變遷影響，水資源供需面臨諸多問題，尤其對南部地區之影響程度最為顯著。民國98年8月莫拉克颱風侵襲，超大豪雨造成南部主要水庫，如曾文及南化兩個水庫集水區之大量沖蝕及崩塌地，水庫淤積量較颱風前增加約1.1億立方公尺，提升了此一地區之災害風險，同時嚴重衝擊到南部地區的水資源系統，對供水穩定性影響甚鉅。將氣候變遷影響納入考量，以強化現有水資源規劃與風險管理決策是當前重要課題之ㄧ，亟需分析氣候變遷對區域水資源供水系統所可能產生之衝擊，並對其進行供水潛能分析，進而提出相關對策以邁向永續發展。 曾文水庫是台灣南部最重要水庫之ㄧ，集水區面積481平方公里，其供水品質攸關民生與經濟。而曾文水庫降雨集中於汛期，每年5月至10月降雨量達全年降雨量之87%。因集水區地形坡陡及降雨集中之情況，導致集水區沖蝕嚴重。再者，土地開發、道路及農路開闢等行為，邊坡穩定性破壞，於颱風、豪雨期間往往導致大量崩塌，崩塌土石流入水庫，造成水庫淤積加速，加上氣候變遷影響對水庫未來供水潛能造成嚴重影響。 因應變遷對曾文水庫所帶來的影響，進而了解曾文烏山頭系統入流及供水潛能，應妥適的分析與評估。爰此，本計畫將探討氣候變遷對曾文烏山頭水庫聯合運用的供水潛能，作為各標的水量調整分配之參據。

Typhoon Morakot hit Taiwan in August 2009 with extreme rainfall. The high intensity rainfall led to extensive soil erosions and landslides in the catchments of two major reservoirs in southern Taiwan, which causes a huge amount of sedimentation (1.1×109 ton) in the reservoirs. The water supply potential is greatly reduced due to the reservoir sedimentation. Since reservoirs are vital water supply facilities in southern Taiwan, the serious sedimentation problems are always main concerns for the water resources system of southern Taiwan. Southern Taiwan receives 90% of annual rainfall during wet seasons but only 10% of annual rainfall occur during dry seasons. The reservoirs play an extremely important role in stabilizing the water supply throughout a year. Moreover, many climate change researches suggest a future with wetter wet season and dryer dry season which might make the issue worse. Hence, assessing the possible impact of climate change on water resources systems is a key task for this project. The following are the major results and findings of the project: 1. Some basic information of Tsengwen-Wusanto reservoir system was collected including rainfall data, runoff data, reservoir operation rules, reservoir rule curves, reservoir operation water loss, water demands, irrigation plans, facility capability and others. 2. Analysis results for the impact of climate change on rainfall and runoff of Tsengwen-Wusanto reservoir system: (1) A conceptual hydrological model, the modified Hydrologiska Byrans Vattenbalansavdelning (HBV), is used to simulate the rainfall-runoff mechanism of the target catchment. This project used the data from 1975 to 1999 for model calibration and the data from 2000 to 2014 for model validation. Three performance indexes (i.e., bias, correlation coefficient and root mean squared error) were used for model assessment in the calibration and validation periods. Overall, the results show that modified HBV model can reasonably simulate the rainfall-runoff mechanism of Tsengwen reservoir catchment. (2) Several statistical tests(i.e.,Mann-Kendall, Mann-Whitney-Pettitt and Kruskal-Wallis tests) are used to detect the trend and change point in rainfall amount and rainy days based on historical record. The analysis results show that there is an increasing trend in rainfall for the period from 1980 to 1999 but there is no significant trend in rainfall for the period from 2000 to 2014. In terms of rainy days, an increasing trend is found for the both periods (i.e., 1980 to 1999 and 2000 to 2014). (3) The results of trend analysis under climate change scenarios suggest: (a) under A1B emission scenario, the future rainfall in mei-yu, summer and monsoon seasons show increasing, no significant and decreasing trends, respectively. (b) under A2 emission scenario, the future rainfall in mei-yu, summer and monsoon seasons show slight decreasing, increasing and slight decreasing trends, respectively. (c) under B1 emission scenario, the future rainfall in mei-yu, summer and monsoon seasons show increasing, increasing and no significant trends, respectively. (4) The analysis results of scenario runoff suggest: (a) under A1B emission scenario, most GCM projection data produce an increase in runoff; (b) under A2 emission scenario, most GCM projection data produce a decrease in runoff and (c) under B1 emission scenario, most GCM projection data produce an increase in runoff. 3. The analysis results relating to the water supply potential of Tsengwen-Wusanto reservoir system: (1) This project reviewed several methods used to estimate the water supply potential of a water resources system. In this project, a reservoir operation simulation model (ROSM) composed of continuity equations and predefined operation rules is used to simulate the water supply processes. Then, the value of water supply potential can be further derived based on the simulation results of ROSM. The project referred to a project of Water Resources Agency, Feasibility Analysis of Tsengwen/Nanhua Reservoir Interconnection Pipeline (Water Resources Agency, 2013) and applied the same system setting in ROSM for results comparison as model validation. A comparison of results indicates the difference in total amount of water supply potential is about 1.56 percent when compared to the previous results. Overall, the results point out that ROSM can reasonably simulate the water supply potential of Tsengwen-Wusanto reservoir system. (2) The current water supply potential of Tsengwen-Wusanto reservoir system for agricultural, industrial and domestic uses are 7.486×109 ton/year, 0.224×109 ton/year and 1.133×109 ton/year, respectively. In general, the total water supply potential is 8.842×109 ton/year. (3) The project assessed the impact of climate change on water supply potential based on various climate change scenarios. The results show MPEH5 projection data under A1B emission scenario produce the worst case with the lowest total water supply potential of 8.441×109 ton/year. In this worst case, the water supply potential declines about 4.5% when compared to the current case. (4) The project addressed the impact of various factors on water supply potential: (a) normal pool level, (b) reservoir capacity and (c) climate change. The analysis results show that the climate change factor has greatest influence on water supply potential; followed by reservoir capacity factor; the factor with least influence is normal pool level. (5) The ROSM results based on current case and current case under consideration of climate change reveal: (a) in the current case, the water deficit is about 1.628×109 ton/year (15.5% of annual water demand) and (b) in the current case under consideration of climate change, the water deficit is about 2.029×109 ton/year (19.4% of annual water demand). Based on the ROSM results of the current case, the most vulnerable crops due to the water deficit are first crop of rice, first crop of sugarcane with intercropping vegetables or field crop, second crop of sugarcane with intercropping vegetables or field crop and third crop of sugarcane.