The potential effect of a 100-year pluvial flood event on metro accessibility and ridership: A case study of central Shanghai, China

The Shanghai Metro constitutes a sizeable share of the municipal public transit. This paper presents a gravity-based approach for evaluating the potential effect of a 100-year pluvial flood (PF) event on metro accessibility and ridership. Since physical geographers have examined PF hazards and human geographers have analyzed metro accessibility separately, we seek to fill the research gap through examining metro accessibility and ridership together under adverse circumstances. To this end, road inundations are initially modeled by FloodMap-HydroInundation2D. Accessibility to metro stations by three access modes (walking, cycling, and driving) is measured through three impedance functions (inverse power, negative exponential, and modified Gaussian). Ridership measure mainly concerns the distance-decay effect on stations' attraction for passengers. The results indicate that inundation depth on more than 95% of the road links would reach 10-20 cm in the PF scenario, and road links with inundation deeper than 20 cm and 30 cm account for 47% and 15% of the road network respectively, which imposes notable restrictions on access journeys especially by cycling and driving. Metro accessibility in central Shanghai is quite equitable, even in the PF scenario. 87% of the communities can access the metro stations at the medium and medium-high accessibility levels in the normal scenario, but 80% can access only at the low and medium levels in the PF scenario. Due to the inaccessibility of neighboring station(s) in the PF scenario, 15 more stations may face the challenge of serving more than 50,000 passengers, which is much larger than their normal ridership. These findings have important implications for the formulation of safer usage of public transport in the face of heavy rainfall and associated flood events.