Spatiotemporal Urban Flood Expansion and Propagation by Percentage of Node in Flood Assessment (PNFA)

Urban pluvial flooding is a complex process shaped by rainfall intensity, drainage system capacity, and urban infrastructure. While previous studies have mapped flood extents, the spatiotemporal evolution of drainage saturation and overflow propagation remain insufficiently explored. This study introduces the Percentage of Node in Flood Assessment (PNFA), integrating the Flood Expansion Rate (FER) to measure flood spread within drainage networks. Using the EPA Storm Water Management Model (SWMM), three historical storms (2008, 2019, 2020) and seven returned period scenarios were simulated in Do Lo, Hanoi, Vietnam. Results reveal that despite variations in rainfall intensity, spatiotemporal flood patterns remain stable, suggesting predictable flood propagation pathways. FER values range from 0.17 (slow) to 0.902 (rapid), indicating that system response is highly sensitive to storm intensity. Key flood-prone areas consistently experience early drainage saturation, pinpointing critical intervention points. Flood propagation speed and saturation timing are crucial for early warning systems and emergency response strategies. This study enhances urban flood risk assessment by incorporating spatiotemporal flood hazard mapping, which considers the sequence and timing of flood events. These insights are crucial for flood mitigation, urban planning, and drainage system resilience, highlighting the importance of time-sensitive flood risk models amid rising extreme weather events.