歷史地區面對洪水災害之韌性評估

Abstract

在全球極端氣候與都市化的影響下，強降雨引發的洪澇災害日益頻繁且難以預測，加上防救災資源的有限性，要降低都市高暴露度下的洪水風險需要透過低衝擊開發與風險評估的非結構性防災調適策略。UNDRR及過去的洪水風險研究定義了韌性城市建構要項，同時提供給決策者於災害期間拯救生命和財產的資源分配建議，但這些評估當中的保護標的卻很少針對文化資產。其原因為文化資產具有無法以貨幣計算的無形價值(歷史、文化、藝術、紀念價值)，當受到衝擊後難以透過維修或重建而回復其歷史價值，遭遇損壞或遺失也會間接造成歷史地區經濟損失。正因為它的不可替代與老舊特性，在估算其韌性時，需要有別於一般建物韌性計算方法並提供相對的治理對策。 本研究以「經破壞後難以復原」及「受洪水影響」之有形文化資產為研究對象，參考 ISO 14090 針對氣候變遷定義之風險，由危害度、暴露度和敏感度為韌性指標中的三大次指標，並整合脆弱度與回復力的概念建立一個具有時變性的洪災韌性指標(Flood Resilience Index, FRI)，評估洪水對歷史地區的文化韌性衝擊。此研究配合高精度且計算快速的3Di模式，模擬臺灣臺北市五個行政區在不同降雨情境下的淹水物理因子，並針對文化資產定義具有時變性與空間變化性的韌性因子，最後，計算FRI供後續擬定調適行動的依據。 研究結果發現區域之間危害度與韌性分數並非成一致的正向關係，證實區域韌性需考量文化損失的必要性，實際風險與地區防洪效率和資產特性密切相關。經比較區域差異，發現中正區為最受文化韌性影響的區域，同時也是FRI分數最低的區域；相反地，最不受文化韌性影響的區域為萬華區，也正好為韌性最佳的區域。根據FRI時變分析，事件期前期受到暴露度影響最多，事件期後期和恢復期則受到危害度影響最多，當區域暴露度影響越小，此轉換會越提前發生，而敏感度在整個事件中影響皆屬相對較低。FRI可幫助決策者(decision makers) 了解區域之間特質的差異，於災前預測指標變化作為災前或災時應變的依據，經由調適行動，提升歷史地區的韌性。

With extreme global climate and urbanization, increasingly frequent and unpredictable floods caused by heavy rainfall, and limited resources for disaster prevention and relief, reducing flood risk in highly exposed cities requires non-structural adaptation strategies for disaster prevention through low-impact development and risk assessment. Integrating UNDRR and past flood risk studies, the Constructive Resilient Cities (CR) definition provides policymakers with recommendations for allocating resources to save lives and property during disasters, but the protection targets of these assessments rarely target cultural heritage (CH). The reason for this lack of attention is that they have intangible values (historical, cultural, artistic, and commemorative) which can not be measured in monetary terms and are difficult to restore through repairs or reconstruction when they are impacted. Because of its irreplaceable and old nature, it requires a different method of calculating its resilience from that of ordinary buildings and provides a relative solution for its management. In this study, tangible CH that are "difficult to recover from damage" and "affected by floods" are used as the target, and the ISO 14090 definition of climate change risk is used to define hazard, exposure, and sensitivity as the three major internal indicators of resilience. Integrating the concepts of resilience and vulnerability, this study establishes a time-varying Flood Resilience Index (FRI) to assess the impact of floods on the cultural resilience of historical areas, This research employs the 3Di model, a numerical model known for its high resolution and computational efficiency, to simulate the physical factors of flooding in five districts of Taipei City under various rainfall scenarios. Additionally, resilient factors, characterized by temporal and spatial variability, are defined specifically for CH. In conclusion, FRI provides a basis for formulating subsequent adaptation strategies. The results indicate an inconsistency between the rankings of hazard and resilience. This underscores the necessity to consider cultural losses when comparing resilience among different areas, as the actual risk is intricately linked to regional flood prevention efficiency and asset characteristics. When we compare the differences among regions, it turns out that Zhongzheng District is the area most affected by cultural resilience, and it also has the lowest FRI score. Conversely, Wanhua District stands out as the area least affected by cultural resilience, coinciding with the highest resilience scores. According to the time-varying analysis of FRI, the early stages of the event phase are most affected by exposure, while the later stages, including the post-event phase and recovery phase, are predominantly shaped by the severity of hazards. The smaller the impact of regional exposure, the earlier this transition occurs, and sensitivity remains relatively low throughout the entire event. The FRI serves as a useful tool for decision-makers to comprehend the distinctive characteristics among regions. It offers a basis for pre-disaster or disaster-time response strategies by anticipating changes in indicators. Through adaptive actions, the FRI contributes to the enhancement of the regional resilience of the ancient city.