**1. Introduction**

Coasts are dynamic systems that change in form at different space and time scales in response to geomorphological and marine forces [1–3]. Coastal landforms, affected by short-term perturbations such as storms, frequently return to their pre-disturbance morphology, thus reflecting a basic, morphodynamic equilibrium [4]. Most coasts are constantly adjusting towards a dynamic equilibrium, frequently adopting different 'states' in response to variable wave energy and sediment supply [5]. Coasts exhibit natural variability in response to changes in environmental factors, which can make it difficult to identify the impact of climate change. Thus, for instance, most beaches across the world show evidence of recent erosion, but ongoing sea-level rise is not always considered to be the major cause. Erosion can result from several other factors, both natural and

**Citation:** Di Paola, G.; Minervino Amodio, A.; Dilauro, G.; Rodriguez, G.; Rosskopf, C.M. Shoreline Evolution and Erosion Vulnerability Assessment along the Central Adriatic Coast with the Contribution of UAV Beach Monitoring. *Geosciences* **2022**, *12*, 353. https:// doi.org/10.3390/geosciences12100353

Academic Editors: Patrick Seyler and Jesus Martinez-Frias

Received: 23 July 2022 Accepted: 16 September 2022 Published: 22 September 2022

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anthropogenic, such as reduced fluvial sediment input [6], offshore bathymetric changes [7], altered wind and wave patterns [8,9], or a mix of factors [10].

The assessment of coastal erosion and flooding is an important issue for the scientific community, considering that a significant and increasing share of the world population currently lives in coastal areas. In fact, the United Nations, during the Ocean Conference 2017 [11], highlighted that more than 10% of the world population (600 million people) live along coastal areas that are less than 10 m above sea level, while about 40% of the world population (2.4 billion people) live within 100 km from the coastline. Moreover, the possible increase of seal level could force the displacement of up to 187 million people globally during this century [12]. As for the Italian peninsula, which has approximately 7500 km of coastline, the data released by the Ministry of Environment, Land, and Sea Protection [13] for the period of 1960–2012 show that 23% (1534 km) of this coastline has experienced erosion, resulting in a total land loss of 35.5 km2.

Assessing coastal evolution and recent erosion trends along with related natural and/or anthropogenic causes is crucial for the correct definition of near-future planning and interventions aimed at combatting erosion and ensuring the sustainable development of coastal zones.

To this end, an appropriate experimental observation of coastal zones with their complex and variable dynamics and configurations is of paramount importance. In this regard, traditional methods suitable for measuring, mapping, and monitoring beach– dune systems and shoreline changes are commonly applied, such as the interpretation of topographic maps and aerial images. Related activities, however, take a long time and immense effort to complete, and they may not provide the necessary spatial scale and local details and/or comprehensively cover the most recent time intervals [14]. Fortunately, such limitations in spatio-temporal resolution are now being overcome, or at least alleviated, thanks to the access to large satellite databases and the development of various technologies appropriate for this purpose. In particular, the progress and easy accessibility of Unmanned Aerial Vehicle (UAV) technology has enabled the development of an alternative coastal monitoring technique that efficiently captures spatial and temporal requirements across a wide range of environmental applications [15–19], with the important added advantage of making the task much less tedious.

This study presents an integrated approach involving traditional methods and the innovative UAV methodology to study the shoreline evolution and morphodynamic behaviour of the Molise coast, a well-known coastal system that has been under continuous study for some decades and one of the most vulnerable coastal regions in Italy (e.g., see [20–22] and references therein).

The major aims of this study are: (i) to assess the spatial-temporal distribution of shoreline changes that occurred along the Molise coast from 1954 to 2016 using remotely sensed data and topographic maps; (ii) to assess long- to short-term shoreline changes of two selected test areas and, by means of UAV-derived data, their most recent shoreline and morpho-topographic beach–dune changes, and (iii) to assess the possible influence of such changes on the vulnerability of the test areas to coastal erosion and inundation.
