An Integrated Risk Assessment Framework for Compound Flooding in Canadian Urban Environments

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Canadian urban environments are prone to compound flood events that result from the interactions between multiple contributing factors including rainfall, runoff, groundwater, sewer backup, and seawater levels in coastal zones. Analysis of different flood generating mechanisms in isolation without proper characterization of their interrelationships can lead to significant underestimations of flood risks. This can severely undermine resilience measures for communities and infrastructure leading to the misallocation of investment in flood protection measures. In this project, we will develop an integrated statistical and physically-based framework to simulate and predict compound flood risks under climate change in urban domains to develop effective mitigation plans. The proposed framework will characterize the dependencies between multiple flood generating mechanisms based on a multivariate statistical approach and will identify rare compound events. We will develop sampling methods to generate boundary conditions from the resulting joint distribution to drive physically based hydrodynamic models. This project will evaluate the added value of coupled hydrodynamic models to represent the combined effects of overland flooding with groundwater infiltration and sewer backup compared to models that do not represent the dynamics between the surface and sub-surface flows. We will drive the hydrodynamic models with an ensemble of boundary conditions generated through the historical and future joint distributions to assess projected changes in compound flood events. The resulting framework will be used to characterize the contribution of each factor to the impacted areas and develop preventive measures for future scenarios considering the effects of more intense hydroclimatic events and sea-level rise due to climate change. In collaboration with the Institute for Catastrophic Loss Reduction (ICLR), we will disseminate the results from the proposed project directly to insurance industry executives and key officials involved in the management of urban flood risks. This project will provide river forecast centres, conservation authorities, insurance industries, municipalities, among other stakeholders with data, rigorous methodology, and personnel to analyze and predict compound flooding and develop robust mitigation plans that will benefit all Canadians.