Analysis of the risk of Transport infrastructure disruption from extreme rainfall

Transport infrastructure networks are increasingly vulnerable to disruption from extreme rainfall events due to increasing surface water runoff from urbanization and changes in climate. The impacts of such disruptions typically extend far beyond the original disaster footprint, because of the increased interconnection and spatial extent of modern infrastructure systems. This paper presents an integrated assessment methodology to quantify the flooding risks from extreme rainfall, measured in terms of expected travel time across the road network. The method is driven by a probabilistic rainfall weather generator that can simulate time series of current and future rainfall. This is integrated with a high resolution urban flood model, CityCAT, to provide information on depth and velocity of floodwater. This hazard layer is combined with empirical analysis of vehicle speeds during a flood, to perturb a transport accessibility model to determine the impact of a given event on journey times. The study assessed the potential impact of flooding on the network performance in relation to macroscopic urban travel times using Newcastle-upon-Tyne (UK) as a case study. Results showed relevant delays for two different hazard scenarios, for a maximum of 24 minutes and 42 minutes respectively. The impacts are significant and implementation of a probabilistic risk-based approach will provide a rational means to prioritise adaptation measures to reduce delays in these circumstances.