## 2 Study Area  
The study area of the present work covers 20 regions of south-western Europe (Figure 1), 12 of the regions located on the Atlantic coast and the rest (8 regions) on the Mediterranean coast, distributed by country as follows:  
* France (3 regions): Poitou-Charentes, Aquitaine and Languedoc-Roussillon.
* Portugal (5 regions): North, Central Region, Lisbon, Alentejo and Algarve.
* Spain (12 regions): Basque Country, Cantabria, Asturias, Galicia, Andalusian Atlantic Coast, Catalonia, Community of Valencia, Region of Murcia, Balearic Islands, Ceuta, Melilla and Andalusian Mediterranean Coast.  
The study area covers 8034 km of coastline (864 km in France, 848 km in Portugal and 6322 km in Spain). Of the coastline analysed, 47.3% corresponds to the Atlantic coast (3807 km) and 52.7% to the Mediterranean coast (4227 km). The total area includes a population of nearly 42 million inhabitants (2021 census), with such important cities (in terms of population and socio-economic activity) as Bordeaux, Poitiers and Montpellier (France), Lisbon and Porto (Portugal) and Barcelona, Bilbao, Valencia and Malaga (Spain).  
There are important differences between the Atlantic and Mediterranean coasts of Southwest Europe. The Atlantic coast is controlled by the powerful forces of tide, wind and waves which have formed a wide range of environment types; wind swept cliffs, exposed rocky headlands and narrow tidal inlets contrast sharply with long stretches of sandy beaches, sheltered bays and extensive intertidal mudflats. The most important rivers of the study area (Loire, Garonne, Douro, Tejo and Guadiana) drain into the sea along the Atlantic coast. The region benefits from an oceanic climate with mild, wet winters, cool summers and predominantly westerly winds. It is a coastline that is undergoing progressive anthropization with increasingly large urban and industrial areas (fisheries are strategic for the regional economy). This puts massive pressure on the natural environments, which include ecosystems of the highest interest, such as the Donana National Park (Southern Spain), the largest wetland in Europe.  
The Mediterranean coast of Southwest Europe has a very step relief due to the proximity of large mountain systems (the Pyrenees and the Baetic Mountains). The landscape includes high mountains and rocky shores, coastal wetlands and sandy beaches. Tides and swell are not as energetic as in the Atlantic, although during the Gloria storm (January 2020)waves of 8.44 m in height were recorded on the coast of Valencia, the record measured in the Mediterranean so far [19]. The climate is characterised by hot, dry summers and cool winters with frequent heavy, short rainfall events. This Mediterranean region is one of the world's primary tourism destinations. The coastline is highly urbanised and has been severely modified. Additionally, there are chronic water shortages and a constant threat of forest fires. The extremely high tourist pressure has threatened enclaves of high ecological value, with the Manga del Mar Menor (Murcia region), the Albufera of Valencia and the Ebro Delta (Catalonia) standing out.  
The economic importance of both coasts derived from tourism must be highlighted in the study area. As significant examples, we highlight the Balearic Islands in Spain, where tourist activity represents 45.5% of the region's GDP; a territory that received 16.5 million tourists in 2019. The Algarve coast in Portugal also represents a growing tourist destination, with slightly more than 9 million tourists for the same year, as well as the Languedoc-Roussillon coastline, with close to 1 million visitors in 2019 [20].