台灣國有森林資源水源涵養經濟效益之評估

Evaluating the Economic Value of Water Conservation by Taiwan National Forests

水資源為人類不可或缺之生存要素，森林生態系亦與人類生活息息相關，而水源涵養便是森林生態系主要功能之一，其效益屬於一種間接利用價值。隨著環境資源被開發與破壞，水資源缺乏的問題逐漸受到重視，評估森林水源涵養功能便成為探討森林水資源永續利用之重要手段。然而評估森林水源涵養功能並不容易，其評估方法易依據不同環境特性等因素而有所差異，如何準確評估近似於現實狀況亦是研究所需著重探討之部分。本研究針對台灣八個國有林區管理處轄下之森林，透過水文平衡收支法以及水庫單位容積造價之重置成本法，分區計算台灣國有林森林每年平均水源涵養總量為29,967,841,946.00 m3，平均每單位蓄水量價格為0.10元/m3，每年涵養水源之經濟效益則約為3,102,671,667.08元。自本研究模擬之結果顯示，台灣國有林水源涵養功能與位處之環境氣候相符，然而於計算過程中發現，即便皆位於本島，不同地區水庫單位蓄水貼現成本可能受地理環境等諸多因素影響，而有較大的差異。因此建議在估算水源涵養時，除了考量資料獲取的尺度及限制外，亦應該顧慮到國內不同地區的水資源供應來源，分別計算後再加總以求更精確的結果。

 

Water is the subsistence of human beings and it can be conserved by forests. The water conservation value is a kind of indirect use value. With the continued consumption of natural resources, the problem of water scarcity has been becoming important. Estimating the value of water conservation becomes critical to investigate the sustainable use of water resources by forest. However, estimating the value of water is difficult. The estimates are easily affected by many factors, such as climate, topography, and data sources. Therefore, it is challenging to estimate the value of water accurately in a practical way. In this study, a water balance model with replacement cost is adopted to estimate the value of water conservation in eight national forest districts in Taiwan. The estimated water conserved in the national forest districts is approximately 29,967,841,946.00 m3 annually and the average cost for reservoirs is NT$ 0.10/m3. The economic value of the water stored in Taiwan’s national forest districts is estimated to be NT$ 3,102,671,667.08 per year. The result of this study indicates that the capability of conserving water by forests conforms to rainfalls generally. In addition, the discounted cost of each reservoir in Taiwan has large variations in the assessment process. This study also suggests that we should consider water sources, in addition to the data scale, to improve the estimation accuracy.