Integrated surface-subterranean hydrodynamic modelling and evacuation risk assessment for urban metro systems under extreme rainfall scenarios

Abstract

Flooding driven by climate change increasingly threatens cities, placing subterranean infrastructure at risk. Existing assessment methods may fail to fully capture the associated flood risks. In particular, they may underestimate the impact on pedestrian evacuation safety in underground spaces. In this study, an integrated multidimensional hydrodynamic framework is proposed to investigate urban flood evolution and intrusion processes in underground spaces. The model is applied to an urban area in Wuhan that is susceptible to severe flooding, incorporating pedestrian risk assessment under extreme rainfall scenarios. Spatiotemporal analysis of floodwater depth and velocity reveals that flooding in underground spaces escalates quickly. The first basement level (B1) becomes submerged to a depth of 0.3 m within the first 5 min. Floodwaters subsequently overflow into the second basement level (B2), reaching the critical floodwater depth by 15 min. The distribution of risk levels shows a significant increase in flood hazard for both adults and children. By 15 min, over 90 % of the B1 area and 96 % of the B2 area are classified as medium or higher risk. Notably, children experience higher and earlier flood risks compared to adults. By the 10-min mark, 70 % of the area for children is classified as high or extremely high risk. In contrast, only 13 % of the same area poses a similar risk level for adults at that time. These findings underscore the urgent need for improved flood risk management and early warning systems to protect urban infrastructure and vulnerable populations, especially children.