The alongshore response of dunes to storm events can be extremely variable and, consequently, their capacity to maintain their services, including the protection of hinterland communities. In this study, the role of biotic and abiotic factors determining the magnitude of dune retreat driven by a severe storm along a 60 km barrier island system was investigated. Data from high-resolution satellite imagery, digital terrain models, and wave propagation models were used in this assessment. The assessed abiotic factors included the backshore volume, dune height, downdrift inlet distance, and incident wave power. The evaluated biotic factor was the vegetation cover, characterized by a vegetation index retrieved from the multispectral imagery. The results revealed large alongshore variability on dune retreat, ranging from negligible impact to ca. 40 m of retreat. All combined factors allowed us to explain up to 70% of the dune retreat variability through a multi-regression analysis. Among all investigated factors, the major contributor controlling the magnitude of dune retreat was the backshore volume (more robust berms reduced the retreat) followed by the wave power (normal and longitudinal components). Moreover, the removal of local salient features in the dune line caused the straightening of the coastline, highly contributing to the development of dune retreat hotspots. The other evaluated factors had a smaller influence on reducing coastal retreat, including the vegetation, whose contribution to dune protection was around one order of magnitude lower than that provided by the backshore volume. The results highlight the importance of regional assessments to understand the causes behind the large alongshore variability of storm impacts at dunes. They also state the relatively low influence of the vegetation from this climatic region to enhance dune resistance to storms.
