Compound Coastal Flood and impact-based Risk Assessment in the Context of Climate Change Using a Multimodel Approach to Enhance Coastal Resilience

In the context of climate change, future coastal flooding will become increasingly impactful, driven primarily by sea level rise and the intensification of extreme precipitation events along coastlines, rather than changes in wind regimes, wave dynamics, or hydrodynamic circulation (IPCC, 2021; Vousdoukas et al., 2018). Due to the vast geomorphological diversity of coastlines and the varying exposure of assets at risk, advanced tools are necessary for precise risk assessments, particularly for urban areas and human settlements.

Coastal flooding dynamics cannot be adequately described solely by barotropic phenomena such as wave setup but require explicit modeling of wave impacts through phase-resolving models. In this work, we propose a compound flooding assessment integrating, at an urban scale and very high resolution (1-5 meters), the effects of storm surge, coastal wave-current interactions, and explicit wave runup simulations using phase-resolving coastal models.

Urban-scale flood risk assessment not only allows the modeling of wave interactions with natural and man-made structures but also incorporates urban elements such as groynes, breakwaters, roads, and buildings. This modeling approach supports the design of ecosystem-based solutions to enhance coastal resilience (Cheong et al., 2013). Additionally, we discuss the integration of hydraulic flooding simulations caused by rainfall and river overflow into compound flooding models, demonstrating how coastal hydraulic risk can be better described—beyond traditional extreme value statistics—using impact-based metrics for compound events (Bevacqua et al., 2019).

We conduct a combined assessment of sea level and wave effects on flooding using a selection of extreme events with varying wave and sea-level conditions. This is achieved through a multimodel approach comparing simulation outputs from FUNWAVE and XBEACH models (Shi et al., 2012; Roelvink et al., 2009). These outputs are used to validate results obtained from a simplified modeling approach developed within the SCORE project, which employs traditional hydraulic models for unsteady flow simulations coupled with phase-averaged wave models for the marine component.

These tools have been applied to the study site of Marina di Massa (Italy) to assess coastal flood risk trends for future scenarios and to design early-warning systems. In Marina di Massa, this approach is supported and validated by an observational system that includes coastal webcams, wave radars, and meteomarine observation systems (buoys and ADCPs).