A multiscale modelling framework of coastal flooding events for global to local flood hazard assessments

Abstract. Tropical and extratropical cyclones, which can cause coastal flooding, are among the most devastating natural hazards. Understanding better coastal flood risk can help to reduce their potential impacts. Global flood models play a key role in this process. In recent years, global models and methods for flood hazard simulation have improved, but they still present limitations to provide actionable information at local scales. In order to address some of those limitations we present MOSAIC, a novel modelling framework that couples dynamic water level and overland flood models. MOSAIC follows a multiscale modelling approach in which local models with high-resolution are nested within a coarser large-scale model to obtain higher-resolution water levels and provide better coastal boundary conditions for dynamic flood modelling. To demonstrate the capabilities of MOSAIC we simulate three historical storm events. To merit the potential of MOSAIC’s multiscale modelling approach we perform a sensitivity analysis. Our findings indicate that various model refinements influence the simulation of total water levels and flood depths. The degree of importance of each refinement is linked to the local topography of the study area, the spatial heterogeneity of the water levels and the storm characteristics. MOSAIC provides a bridge between fully global and fully local modelling approaches, paving the way towards more actionable large-scale flood risk assessments.