A multi-component approach to predict erosion susceptibility of rocky coasts: marine, terrestrial and climatic forcing. An application in Southern Italy

Rocky coasts represent the most widespread coastal environment and, under the present accelerated sea-level rise scenario, are suffering huge impacts in terms of erosion. This type of coastline, like all coastal environments, is subject to the effects of a wide range of marine and terrestrial processes that continually reshape them over time.

This research aims to propose a new methodological approach for assessing the susceptibility of rocky coasts to forcing factors that may be exacerbated by ongoing climate change.

The proposed method is based on the combination of two indexes, i.e., the Physical Element Index (PEIx), which considers the main morphological and geotechnical characteristics of the cliff and determines its proneness to erosion, and a Cliff Forcing Index (CFIx), which describes the marine forcing agents affecting the considered coastal sector.

Firstly, several variables were selected according to previous studies to construct the two matrices. Then, a specific weight factor (Wfi) was attributed to each variable, i.e. each one of the Physical Elements and Forcing Agents considered, according to their specific relevance/contribution to cliff erosion susceptibility. In the last step, the two matrices were interpolated to obtain the final Susceptibility Index (CSIx).

The approach was applied to different coastal sectors located along the southwestern coast of Italy, in the regions of  Campania, Calabria and Sicilia. The different study sectors were selected since they differ in geological, geomorphological and forcing/dynamic settings.

The analysis demonstrated that 6% of the coastal sectors fell in the “Very Low” class of susceptibility (Class 1), 38% belonged to the “Low” class (Class 2), 28% to the “Medium” (Class 3), 22% to the “High” (Class 4) and the remaining 6% belonged to the “Very High” class (Class 5) of susceptibility.

The proposed index-based method, which was finally validated through the comparison of obtained results with recorded cliff erosion rates, is valid for classifying a diverse array of cliffed areas placed in both temperate and equatorial environments.

In addition, the method allows also to get useful information for appropriate spatial planning in areas that have not been anthropised yet and to prevent the development of infrastructure in areas of high susceptibility that can be identified as “hotspots” that require sound monitoring strategies and, at places, immediate protection actions.