農田水利基礎工程全生命週期碳盤查方法之建構 ──以案例驗證比較傳統與生態工程減碳效益

Abstract

為回應《氣候變遷因應法》所揭櫫 2050 淨零排放目標，農田水利基礎工程亟須從傳統「營運碳」視角，轉向涵蓋材料、生產、施工、營運、拆除暨循環再利用的全生命週期碳治理。然現行《水利工程減碳作業參考指引》與《農村水保工程減碳作業指引》僅盤點建材投入與部分施工、拆除工序，缺漏建材/機具運輸、長期營運管理、部分拆除與再利用等模組，易低估實際溫室氣體排放且恐觸發綠色漂洗風險。 本研究採用生命週期評估LCA為核心方法，整合ISO 14067產品碳足跡原則、EN 15978 A1~D模組流程與ILCD資料品質矩陣，並依PCR 2019:14 Construction Product延伸「Cradle‑to‑Grave + D」系統邊界；同時導入PAS 2080以「碳預算」管理之思維，發展一套Excel‑based碳盤查工具。方法學探討工程相關係數庫、蒙地卡羅不確定性分析與植栽碳匯及其他減碳效益獨立報告以避免重複計算，可即時輸出專案絕對排放量、功能單位排放強度與年度碳額度對齊報表，協助主管機關與承攬廠商在標案評分、採購門檻與營運績效評估中落實科學量化。 實證部分以鋼筋混凝土矩形渠道(傳統工法)與導入Nature‑based Solutions(NbS)的漿砌石-植生坡面生態工法為對照。結果顯示，傳統工法四十年全生命週期排放量約為一千噸二氧化碳當量；生態工法透過工法與材料替換，且排除植栽長期碳匯與D模組之減量效益，於全生命週期累計減排可達三成。熱點分析指出，混凝土、鋼筋用量與結構翻新仍為主要排放來源。 研究進一步將盤查結果映射至Avoid–Switch–Improve階層：避免(低碳設計)、替換(生態工法)、改善(再生材料)，並示範如何以碳預算制度管控「規劃—設計—竣工—營運」四階段排放。方法學亦探討植栽碳匯防重複計帳機制，確保同一生態單元之效益不被多專案重複宣稱。 綜合而言，本研究首創涵蓋A~D模組之農田水利基礎工程碳盤查框架與工具，驗證NbS之生態工法於排水渠道之替代效益，並將量化結果直接嵌入PAS 2080管理，衍生「碳預算」之「碳決算」之閉環治理架構，為臺灣農業基礎設施邁向2050淨零目標提供科學化、可追溯且可操作之決策依據。

To align with the 2050 net‑zero target stipulated in Taiwan’s Climate Change Response Act, carbon governance for agricultural hydraulic infrastructure must expand beyond the traditional “operational‑phase” perspective to a full life‑cycle approach that encompasses material production, transportation, construction, operation, decommissioning, and circular reuse. Current national guidelines—Reference Guide for Carbon Reduction in Hydraulic Engineering and Reference Guide for Carbon Reduction in Rural & Soil‑and‑Water Conservation Engineering—inventory only building‑material inputs and selected construction or demolition processes, omitting modules such as material/ machinery transport, long‑term maintenance, and end‑of‑life reuse. These omissions can lead to systematic under‑estimation of greenhouse‑gas (GHG) emissions and heighten the risk of greenwashing. This study employs life‑cycle assessment (LCA) as its central methodology, integrating the ISO 14067 product–carbon‑footprint principles, the EN 15978 module sequence (A1–D), and the ILCD data‑quality matrix, while extending the system boundary to a “cradle‑to‑grave + D” scope in line with PCR 2019:14 Construction Products. Concurrently, a PAS 2080‑oriented carbon‑budgeting and management approach underpins the development of an Excel‑based carbon‑accounting tool. The methodological framework encompasses the construction of engineering‑specific emission‑factor libraries, Monte Carlo uncertainty analysis, and separate reporting of vegetation carbon sinks and other mitigation benefits to avert double counting. The tool instantly generates absolute project emissions, functional‑unit emission intensities, and annual carbon‑budget alignment tables, thereby enabling regulators and contractors to apply rigorous quantitative metrics in bid evaluation, procurement thresholds, and operational‑performance assessment. The empirical analysis juxtaposes a conventional reinforced‑concrete rectangular channel with an ecological alternative that combines masonry lining and vegetated slopes in accordance with Nature‑based Solutions (NbS) principles. Over a 40‑year life cycle, the conventional method emits 1,003,556.43 kg CO2e. By substituting construction techniques and materials—and excluding long‑term vegetation sinks and module D benefits—the NbS alternative achieves a 31% emission reduction within entire life cycle. Hot‑spot analysis indicates that concrete production, reinforcing‑steel consumption, and structural refurbishment remain the dominant sources of greenhouse‑gas emissions. Results are further mapped onto the Avoid–Switch–Improve hierarchy: Avoid (low‑carbon design), Switch (ecological methods), and Improve (recycled materials). A demonstration shows how a carbon‑budget regime can govern emissions across the planning, design, completion, and operational phases. The study also proposes safeguards against double counting of vegetation carbon sinks, ensuring that the mitigation benefits of a single ecological unit cannot be claimed by multiple projects and thereby mitigating greenwashing risks. In sum, this research pioneers the first carbon‑accounting framework and tool that fully cover Modules A~D for agricultural irrigation infrastructure, empirically validates the substitution benefits of NbS‑based ecological methods for drainage channels, and embeds the quantified outcomes directly within the PAS 2080 management process. The resulting closed‑loop governance cycle—from carbon budgeting to carbon accounting—provides science‑based, traceable, and actionable evidence to guide Taiwan’s agricultural infrastructure toward the 2050 net‑zero goal.