Page | 1 Flood Impact to Urban Transport Networks Considering the Flooding Propagation- A case study of Beijing, China Yimeng Liu1,2, Alistair Ford1, Richard Dawson*1, Saini Yang*2 1 School of Engineering, Newcastle University, Newcastle upon Tyne, UK 2 Beijing Normal University, Beijing, China GISRUK 2023 Summary Urban transport networks are vulnerable to surface water flooding, leading to impacts on economic activities, social well-being and the environment. This paper describes a flood-impact-assessment method to comprehensively assessed the economic impacts of traffic disruption from flooding in terms of time delay, fuel consumption and pollutant emission. Urban flooding in Beijing is simulated using the CADDIES-2D model, and impacts are propagated onto the transport network for assessment using the SUMO agent-based transport model. Comparing the economic damage of the baseline traffic scenario with that of three flooded scenarios, it’s demonstrated that rainfall occurring at 7 a.m. induces four times more cost than the baseline. The rain of the same intensity and duration occurring at 8 or 9 a.m. lead to a cost increase for 37.33% and 13.21% respectively. KEYWORDS: urban flooding; impact assessment; traffic simulation 1. Introduction Surface water flooding is an important and impactful weather-related challenge facing cities, which will increase under future climate change (Dodman, 2022). Such flooding, caused by extreme rainfall events, can induce substantial impacts on transport networks and affect their users (Hunt and Watkiss, 2010), but less attention is given to quantifying the impact of the flood induced by rainfall events that occurs at different times of day. This research developed a method in response to this challenge that comprehensively assesses the economic impacts of traffic disruption from the perspectives of time delay, fuel consumption and pollutant emission. This method was applied to Beijing, quantifying the economic damage when the flood occurred at different times of the morning peak. Such a method could assist local and national government to better understand the traffic cost mechanism and assist the optimisation of investment and targeting limited resources at critical locations, enabling adaptation strategies to be gradually implemented over the longer term to realise citywide resilience. 2. Methodology 2.1. Flood Modelling Flood events are simulated with CADDIES-2D flood model (MICHELE GUIDOLIN et al., 2012). This model produces the spatial extent of the simulated flood event, and a time series of hazard maps showing water depths (in metres) and extent of flooding across the model domain. Simulations were undertaken for a 1-in-5 year event of one hour duration across the Greater Beijing region (within the scope of Beijing's fifth ring road, covering an area of 900 km2) The simulation is facilitated by 5m-horizontal-resolution DEM, land-use data, soil porosity, and other characteristic parameters allowed more realistic simulation of flow paths in urban areas. The spatial resolution of output flood maps is 30-meter, and the time resolution is 10 minutes. The CADDIES-2D model was calibrated and validated by comparing a model simulation of 21st July 2012 pluvial flash