Spatiotemporal urban flood expansion and propagation by the percentage of nodes in flood assessment (PNFA)

ABSTRACT Urban pluvial flooding is influenced by rainfall intensity, drainage capacity, and urban infrastructure. While prior studies mapped flood extents, the spatiotemporal dynamics of drainage saturation and overflow remain underexplored. This study introduces the percentage of node in flood assessment (PNFA) and flood expansion rate (FER) to quantify flood spread within drainage networks. Using EPA SWMM, three historical storms (2008, 2019, and 2020) and seven return-period scenarios were simulated in Do Lo, Hanoi, Vietnam. The results show that despite rainfall variability, spatiotemporal flood patterns remain stable, indicating predictable propagation pathways. FER values ranged from 0.17 (slow) to 0.902 (rapid), reflecting flood expansion speed under light to heavy rainfall. Spatiotemporal analysis produced hazard maps, capturing both spatial and temporal dimensions, revealing not only a persistent critical hotspot near AH13 but also consistent flood evolution patterns across various scenarios. These findings shift perspectives on flood preparedness by emphasizing timing, sequence, and hotspot stability. This study advances urban flood risk assessment through spatiotemporal hazard mapping, offering insights essential for mitigation, urban planning, and drainage resilience. Incorporating time-sensitive models is crucial for managing flood risks amid increasing extreme weather events.