Hehan Zhou
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R06 → How Form Shapes Resilience: Simulating and Explaining Urban Flooding
Keywords:#Urban Morphology#Flood Resilience# MIKE21 Simulation#SHAP#Feature Attribution# Year:2025 This is the content of Chapter 5 of the master's thesis.


CAUSAL INSIGHTS INTO URBAN MORPHOLOGY AND  
FLOOD RESILIENCE
This study investigates how urban morphological features influence flood resilience under extreme rainfall. By integrating numerical simulation (MIKE21) and model explainability (SHAP), we uncover the causal relationships between spatial form and compound water risk, offering data-driven guidance for resilient urban design.
METHODOLOGY: From Simulation to Interpretation
A total of 2,280 urban blocks were simulated under multiple extreme rainfall scenarios using MIKE21 to generate flood depth outputs. Fourteen morphological indicators—including building density, green space fragmentation, road proportion, and terrain variation—were extracted for each block. Three flood resilience metrics were defined:
  • Resist: proportion of area with water depth < 0.3m
  • Mloss: marginal increase in flood loss across scenarios
  • Aextreme: adaptive performance under peak inundation conditions


    • Key Findings
  • Building density (DB) positively influences flood resistance by reducing flood-prone open surfaces.
  • Green space fragmentation (GDI) strongly correlates with increased flood loss.
  • Drainage network density (Dr) and slope variation (SD) improve resilience under extreme rainfall.
  • SHAP analysis reveals that feature contributions vary across different flood indicators and rainfall intensities.


    •  Model Explainability
    SHAP values derived from XGBoost were used to quantify the marginal contribution and direction of each morphological variable in relation to each resilience indicator. These results provide a more transparent view of how form shapes resilience.
    Visualizations highlight the shifting importance of features such as DB, ISC, GDI, and GD across rainfall scenarios.

    Design Implications
    Toward Morphology-Driven Flood Resilience
    Findings suggest that spatial form optimization plays a crucial role in enhancing urban flood resilience. Design strategies include:
  • Promoting coherent and compact building patterns
  • Reducing fragmentation and enhancing connectivity of green spaces
  • Preserving slope continuity and drainage capacity
    These insights support a transition toward proactive, morphology-based urban adaptation strategies.

    • Interpretable Machine Learning Workflow