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

加拿大城市环境容易发生复合洪水事件，这是由多种因素（包括降雨、径流、地下水、下水道备用和沿海地区海水水位）之间的相互作用造成的。孤立地分析不同的洪水生成机制，而不适当地描述它们之间的相互关系，可能会导致严重低估洪水风险。这可能严重破坏社区和基础设施的抗灾措施，导致防洪措施投资分配不当。在这个项目中，我们将开发一个综合的统计和物理为基础的框架，模拟和预测在气候变化下的城市地区的复合洪水风险，以制定有效的缓解计划。拟议的框架将表征多个洪水生成机制之间的依赖关系的基础上，多元统计方法，并将确定罕见的复合事件。我们将开发采样方法，以从所产生的联合分布中生成边界条件，从而驱动基于物理的流体动力学模型。本项目将评估耦合水动力学模型的附加值，与不代表地表和次地表流动之间动态的模型相比，耦合水动力学模型代表地表洪水与地下水渗透和下水道备用的综合影响。我们将通过历史和未来联合分布生成的边界条件集合来驱动水动力模型，以评估复合洪水事件的预测变化。由此产生的框架将用于描述每个因素对受影响地区的影响，并为考虑到气候变化造成的更强烈水文气候事件和海平面上升的影响的未来情景制定预防措施。我们将与减少灾害损失研究所（ICLR）合作，将拟议项目的结果直接传播给保险业高管和参与城市洪水风险管理的主要官员。该项目将为河流预报中心、保护当局、保险业、市政当局以及其他利益相关者提供数据、严格的方法和人员，以分析和预测复合洪水，并制定使所有加拿大人受益的稳健的减灾计划。

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.