A composite index framework for compound flood risk assessment

Compound flooding, which is driven by both inland and coastal forcing, poses an increasing threat to coastal regions. However, the current preliminary flood risk assessments under the EU Floods Directive (FD) focus primarily on single-driver events, often overlooking compound flooding risks. Here we introduce a cost-effective framework to identify and rank areas of potential significant flood risk (APSFRs) on the basis of their compound flooding potential. The framework uses a composite index that considers intensity, correlation and probability, along with a cluster analysis, to categorize the APSFRs by dominant flood mechanisms. Using the 1,600 km Spanish Western Mediterranean coastline as a case study, the framework is used herein to identify three key regions with high compound flood potential, with 11% of the 214 analyzed APSFRs falling into the most severe category. The results demonstrate the ability of the proposed methodology to pinpoint areas where high-resolution flood risk assessments are needed and support the efficient integration of compound flooding analysis into the third implementation cycle of the FD. Central Valencia, northern Catalonia and eastern Andalusia are regions at greatest risk of compound flooding along the Spanish Mediterranean coast, according to a framework which incorporates numerous indices to address the multifaceted nature of compound flooding