臺灣因地處亞熱帶季風區及位於板塊交界地帶，地形起伏大、降雨時空分布不均，致使淹水災害頻仍，特別在氣候變遷下，極端降雨事件更具強度與頻率，對都市排水與交通通行構成重大挑戰。近年重大水患事件中，道路通行中斷與居民避難困難屢見不鮮，反映傳統依據靜態最大淹水圖為基礎之避難規劃難以應對實際洪水動態。本研究旨在建構一套結合淹水歷程與道路通行性之疏散評估流程，針對災時避難服務水準進行量化分析，並以臺南市急水溪流域為例，提出具實務性與時間歷程之分群避難策略。本研究首先以SOBEK水文水理模式進行洪水模擬，設定短延時（200 mm/3 hr）與長延時（350與500 mm/24 hr）三組降雨情境，取得各時間點之水深分布。再者，透過ArcGIS Pro及Python模組處理淹水結果與道路路網資料，依路寬與水深資訊建立「道路淹水影響等級」（Road Flood Impact Level），評估各時點道路可通行性。於避難需求分析方面，本研究考量建物樓層與水深，篩選出具撤離需求之保全對象，並利用Closest Facility與Connected Component等演算法分析其可行避難路徑，進一步將保全對象依路徑重疊比例進行分群，依所經路段淹水程度判定其「提前避難」、「災前避難」與「標準避難」等啟動時機。研究結果顯示，急水溪流域中下游平原地區之主要道路於洪水期間通行性下降，次要道路則成為災時的替代道路。在短延時降雨情境下，需進行災前避難的對象相較於長延時降雨情境顯著增加，標準避難對象則有減少趨勢，顯示短延時強降雨對於道路通行會帶來較大的衝擊，加速提前避難的時機。本研究方法經柳營與學甲地區測試驗證，結果符合實務應用與具操作可行性，亦具有應用於其他都市及流域地區之潛力。　
綜合而言，本研究貢獻如下：(1) 建立一套動態淹水與道路通行性整合評估架構，補足靜態淹水潛勢圖之侷限；(2) 發展可操作化的通行風險指標（Road Flood Impact Level），並具時間歷程特性；(3) 引入建物特徵與避難分群策略，提升避難需求評估之精度與實務性；(4) 提出具階段性之避難啟動時程建議，強化地方政府與社區組織應變規劃依據。未來建議將本評估成果與即時災害資訊整合進入數位通訊系統，以提升避難資訊普及率；並於實務應用中納入行動不便者與高齡族群等保全對象與社會面參數，增進評估結果之全面性與社會包容性。

Taiwan is situated in a subtropical monsoon region and located at the junction of tectonic plates. Its complex topography and uneven spatiotemporal distribution of rainfall result in frequent flooding disasters. In particular, under the influence of climate change, extreme rainfall events have become increasingly intense and frequent, posing significant challenges to urban drainage systems and road accessibility. In recent years, severe flood events have often caused road blockages and difficulties in resident evacuation, revealing the inadequacy of traditional evacuation planning based on static maximum flood potential maps in addressing the dynamic nature of real flood processes. This study aims to develop an evacuation assessment framework that integrates flooding processes and road accessibility, conducting quantitative analyses of evacuation service levels during disasters. Using the Jishui River watershed in Tainan City as a case study, the research proposes a practical and time-based group evacuation strategy. The study first applies the SOBEK hydrologic-hydraulic model to simulate flood scenarios under three rainfall conditions: short-duration (200 mm/3 hr) and long-duration (350 mm and 500 mm/24 hr). Water depth distributions at different time intervals are obtained accordingly. Furthermore, flood simulation results and road-network data are processed using ArcGIS Pro and Python modules to establish a “Road Flood Impact Level” based on road width and water depth, which is used to evaluate road accessibility at each time point. In terms of evacuation demand analysis, the study considers building height and water depth to identify protected objects requiring evacuation. Using network analyses and algorithms such as Closest Facility and Connected Component, feasible evacuation routes are identified. These protected objects are subsequently grouped based on route overlap ratio, and their evacuation timing is determined according to the flooding severity along the evacuation routes, categorized into “Early evacuation,” “Pre-event evacuation,” and “Standard evacuation.” The results indicate that during flood events, the main roads in the midstream and downstream plains of the Jishui River watershed experience reduced accessibility, while secondary roads become critical alternative routes. Under short-duration rainfall scenarios, a greater number of protected objects require pre-event evacuation compared to long-duration scenarios, while standard evacuation cases decrease. This indicates that intense, short-term rainfall has a more severe impact on road accessibility, necessitating earlier evacuation initiation. The proposed methodology was tested in the Liuying and Xuejia urban planning area, demonstrating both practical applicability and operational feasibility, with potential for broader application in other urban and watershed areas.

In summary, the contributions of this study are as follows: (1) it establishes an integrated dynamic assessment framework for flooding and road accessibility, addressing the limitations of static maximum flood potential maps; (2) it develops an operational road accessibility risk indicator, Road Flood Impact Level, with time series characteristics; (3) it incorporates building attributes and evacuation grouping strategies to enhance the accuracy and practicality of evacuation demand assessments; and (4) it proposes a phased evacuation initiation schedule to support evacuation planning for local governments and community organizations. Future work suggests integrating the proposed assessment framework with real-time disaster information through digital communication systems to enhance the dissemination of evacuation alerts. It is also recommended to include vulnerable groups, such as people with mobility impairments and the elderly, along with broader social parameters in practical applications to improve the comprehensiveness and inclusiveness of the assessment results.

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