*3.1. Evaluation of Shoreline Changes through the DSAS Tool*

The digitization of the Molise shorelines was carried out in the ArcGIS environment using aerial photos from 1954, orthophoto maps from 2004, and images taken by Google Earth in 2016 (Table 2).

**Table 2.** Data sources used to calculate the shoreline variations in the test areas. RMSE = root mean square error.


Regarding the shorelines of the test areas in 2019, 2020, and 2021, we used the orthophoto images realized by the UAV surveys performed during this study, as shown below. As the test areas are part of a microtidal environment, the shoreline positions were defined as the water line at the time of the photo [33], but a maximum uncertainty of ±1.6 m was assumed for the daily water line position, as it was not possible to reconstruct the tidal conditions for each image.

To evaluate shoreline changes, we used the Digital Shoreline Analysis System (DSAS), a freely available extension to ESRI's ArcGIS [34]. This tool, which automatically creates regularly spaced transects, provides two parameters. First, a distance parameter (Net Shoreline Movement—NSM) that measures the distance between the oldest and the youngest shoreline considered for each transect, and second, the Linear Regression Rate (LRR), which represents the average rate of accretion or erosion obtained after fitting a least-square straight line to each shoreline section, for each considered period. In detail, shoreline variations were determined for the Molise coast by using 352 transects placed at an equidistance of 100 m. As we needed a lot more details for the test areas, we fixed an equidistance value of 5 m.
