區域性水資源耗用衝擊特徵模式之建立

Abstract

生命週期評估可系統性地量化人為活動對環境的影響。此評估架構內的水資源耗用衝擊評估，係為量化由水資源取用導致的供水不足，進而造成的環境影響。現有水資源耗用衝擊特徵模式及特徵因子的建置，未考量資源取用區與資源需求區相異之特性；且水資源供給短缺的影響對象之不均質分布，亦未於模式中呈現。上述空間問題，將使特徵因子的應用受限及影響評估結果的闡釋。 本研究目的為建置區域性水資源耗用衝擊特徵模式。研究中提出集水區影響範圍 (Watershed-Affected Area, WAA) 概念，以呈現集水區及其供水轄區間的空間關係；並選用社會經濟資料描述損害受體於供水轄區內的空間分布。區域性特徵模式的基本架構即是以集水區影響範圍為基礎，並藉由矩陣運算將宿命因子、暴露因子及影響因子等參數的空間屬性納入考量。 研究中以淡水河、濁水溪及高屏溪集水區為案例，以民生、農業及工業部門為水資源耗用損害承受受體，建置各集水區於豐、枯水期的特徵因子；並以水資源經濟價值為指標，量化水資源耗用對各用水部門的影響。案例中以自來水供水系統及灌溉系統資料建置集水區影響範圍；以用水量、人口數與用地面積及產業關聯表分別推估具空間屬性之宿命因子、曝露因子及影響因子。 案例結果顯示，以豐水期 (5月~10月) 新北市板橋區民生部門之特徵因子 NTD 200.37/ m3consumed 為例，其意義為：豐水期於淡水河集水區取用水資源 1 立方公尺，且不排回原集水區時，板橋區民生部門因而無法取得足夠用水的附加價值損失為 200.37 元。而豐水期於淡水河集水區取用水，其影響範圍內民生部門的總損害則為 NTD 3,121.2/ m3consumed。 由此可知，區域性特徵因子具空間屬性轉換特性：輸入集水區尺度之水資源耗用盤查資料，輸出結果將以行政區尺度呈現；且可描述水資源耗用損害於集水區影響範圍內的潛在分布。水資源盤查資料常以集水區為空間尺度，但為使評估結果適用於水資源耗用後的衝擊調適或補償施行，行政區尺度的結果將更具有支援決策的應用價值。此即為本研究所建置之特徵因子的主要貢獻。 研究中亦將區域性特徵因子應用於水稻種植灌溉用水評估、再生水供水效益評估及季節性水價制定，探討衝擊評估結果如何輔助區域水資源管理。結果顯示，有別於供水量，水資源耗用衝擊評估因隱含評估地區的水資源條件，結果能描述水資源耗用造成的後續影響，適用於從集水區或行政區角度的管理，例如：水資源管理及分配或休耕補償等。 本研究解決的空間問題其重要性為：於計算特徵因子時，因已知潛在受體及其分布，而能使用正確的受體資料，進而提高特徵因子的代表性及評估結果的準確度。並且，因具有詳盡損害量化及受體空間資訊之評估結果，不僅可用於生產端的方案決策，亦有助於損害受體端的災害預防及區域治理。

Life Cycle Assessment (LCA) is a systematic method for evaluating the impacts of human activities. Under the framework of LCA, the impact of water consumption intends to quantify the environmental burden due to insufficient water supply resulting from water consumption. Yet, two spatial problems were identified in the current LCA framework, particularly for the application of characterization models and characterization factors (CFs) for the impact of water consumption. The presence of spatial differences between the water-providing watershed and the water demand regions, and the distribution of damage receptors in the research area, may hinder interpretation of the impact results. This study aims to establish a regionalized characterization model of water consumption impact under the LCA framework. The characterization model was developed based on Watershed-Affected Area (WAA), which represents the relationship between a watershed and its supply areas. Socio-economic data describing the distribution of damage receptors in the water supply area was also adopted in the characterization model. The model was operated in matrix form, considering the complexity of spatial attributes such as fate factor, exposure factor, and effect factor. This regionalized characterization model was demonstrated on the Tamsui River, the Zhuosui River, and the Gaoping River in Taiwan. The domestic sector, the agricultural sector, and the industrial sector were defined as damage receptors in the case study. Besides, the economic value of water was selected as an indicator to understand the impacts of water consumption on each sector. The WAA was constructed by analyzing the potable water supply system and the irrigation system. The water demand data, land use area, and the Input-Output tables were used to derive fate factors, exposures factors, and effect factors, respectively. Take the Tamsui River as an example: the CF of the domestic sector in Banqiao District, New Taipei City, was NTD 200.37/ m3consumed during the high-flow period (May-October). This result indicated that consuming 1 m3 of water in the Tamsui River during this period would cause insufficient water supply to the domestic sector in Banqiao District and result in the loss of NTD 200.37 of added value. Moreover, the total loss of added value of the whole domestic sector in the WAA of the Tamsui River would be NTD 3,121.2. From the results of the regionalized CFs, it was learned that this model enabled the transformation of impacts from different scales, that is, inputting water consumption inventory data at a watershed scale and outputting damage results at a local administrative scale. This model could also be used to reveal the distribution of water consumption impacts at the regional level. These are the main contributions of this study, as the impact results at administrative scale could improve easiness in supporting decision-making. To further understand the feasibility of the developed CFs in regional water resources management, scenario studies on the influences of irrigation water demand for paddy rice, implementation of wastewater reclamation plants for water supply augmentation, as well as for possible formulating of seasonal water pricing, were conducted. Results from the impact assessment reported the consequences of water consumption rather than quantitative results of water supply resulting from the inclusion of water characteristics data. Therefore, compared to the volumetric outputs, the impact results could provide more information to support water resources management such as water resource distribution or subsidies for fallow farmland. The regionalized characterization model developed in this study is expected to improve the quality of the CFs and their impact results, mainly due to the consideration of known spatial features of damage receptors in the model. The results with detailed spatial information can be used not only for the selection of alternative practices but also for improving regional governance and drafting damage prevention strategies.