Optimizing CVI-based heuristic approach for regional coastal vulnerability assessment in &#160;Sicily and 2000-2019 shoreline change calibration.&#160;
Authors: Azzara Grazia , Manno Giorgio , Martinello Chiara , Basile Mirko , Mercurio Claudio , Lo Re Carlo , Ciraolo Giuseppe , Rotigliano Edoardo 
Published: June 2022

&lt;p&gt;Coastal vulnerability can be defined as its proneness to be damaged by changing climatic&amp;#160; and/or geomorphic conditions. In this study, coastal vulnerability focuses entirely on the&amp;#160; physical impact of erosion, distinguishing the coastal behaviour between negative&amp;#160; (susceptibility) and positive (resilience) responses to climate change-induced conditions,&amp;#160; without taking into account any socio-economic variables.&amp;#160;&lt;/p&gt;&lt;p&gt;The Coastal Vulnerability Index (CVI) approach has become one of the most used and simple&amp;#160; assessing method for coastal regions around the world. CVI approach requires the selection&amp;#160; of a set of critical variables which are expected to significantly drive system processes, which&amp;#160; are then reclassified assigning to each obtained class a score expressing its expected&amp;#160; incidence, following to an expert based analysis. In this study we propose a modified version&amp;#160; of the CVI approach, for application to the entire coastline of Sicily as a first-pass regional scale coastal-vulnerability assessment. In particular, we modified the set of considered&amp;#160; variables, maintaining coast classification and slope, but excluding the shoreline change,&amp;#160; which was rather used for validating the obtained model. At the same time, long term or&amp;#160; negligible variables (sea level change and tidal range, respectively) were not considered and substituted by three covariates much more directly related to the short-term sea wave energy&amp;#160; (number of storm surges; mean wave power; dominant wave direction). Finally, a new&amp;#160; variable expressing the sediment yield from the fluvial system was also included, exploiting&amp;#160; the estimation offered by the Watem-Sedem model. To apply the CVI at a regional scale,&amp;#160; centroids along the coastline were generated and the vulnerability class for each factors&amp;#160; captured, so to compute the composite vulnerability CVI, which was reclassified into its four&amp;#160; quartiles.&amp;#160;&lt;/p&gt;&lt;p&gt;By crossing the obtained CVI classes and the observed 2000-2019 shoreline variation, a largely&amp;#160; satisfactory validation of the heuristic model was obtained, with the advancing and retreating&amp;#160; coastal sectors being strongly concentrated in the I and IV CVI classes, respectively. A general&amp;#160; negative trend between advancement and CVI score prediction arose from class I to class IV,&amp;#160; with a less marked discrimination between class II and class III. At the same time, it was&amp;#160; observed how the sediment yield factor allowed to correctly classify some advancing coastal&amp;#160; sector, which otherwise would have been predicted as subjected to retreatment.&amp;#160;&lt;/p&gt;&lt;p&gt;The obtained results produced a reliable picture of the regional coastline status, posing also&amp;#160; the basis for potential steps toward a stochastic modelling of coastal erosion processes in&amp;#160; Sicily.&lt;/p&gt;