## 2 Study Area  
This work focuses on the coastline of Guardamar del Segura located in the southeast of Alicante, Spain, on the Mediterranean coast (see Figure 1). The area has a population of more than 16,000 inhabitants, and the main economic activity in the region is summer tourism. The studied coast includes the beaches of Los Viveros (corresponding to zone B in Figure 1c) and Babilonia (zone C in Figure 1c). These two beaches have an actual length of 2.7 km and an average width of 12 m, reaching a maximum of 35 m. They are open beaches of golden sand with a grain size of around 0.27 mm [20], which is between fine and coarse sand. Guardamar del Segura coast is a fetch-limited environment with a predominance of sea waves. This coast is an environment with small astronomical tides (as is common in the Mediterranean) that oscillate about 0.3 m (SIMAR data from Puertos del Estado [21]). However, the so-called meteorological tides can reach up to 0.45 m. The dominant wave direction is northeast, creating a net N-S-oriented coastal current. Significant wave heights in this area, from 1958 to 2023, are 50.80% of the time between 0 and 0.5 m, 37.52% between 0.5 and 1 m, 8.7% between 1.0 and 1.5 m, 2.06% between 1.5 and 2.0 m and the remaining 0.92% between 2.0 and 3.5 m [21]. It should be noted that according to the available data [21], the maximum monthly values up to 1970 did not exceed 3 m of significant height. In the 1980s, there were already some peaks that exceeded 4 m, a trend that remained constant with peaks between 2.5 m and 4 m until 2010, but with an average value of around 2 m.  
Figure 1: (**a**) Location of the study area. (**b**) Orthomosaic of the coast in 1930 and details of the transects used in the study. (**c**) Orthophoto of the coast in 2022. Note that the coordinates used are UTM ETR89 H30N. However, in the last 13 years, the average has risen around 3 m with some peaks in 2019 of almost 7 m. The latter peak is due to the large Isolated Depression at High Levels (DANA in Spanish) that occurred in the area in 2019 [22]. As for the peak period, the histogram is centered on the 5-6 s interval (23.94% of the time), distributed on the 2-4 s interval (29.12%) and then on the 4-5 s interval (19.59%), 6-7 s interval (17.89%) and 7-10 s interval (17.43%). According to the latest data published by the Intergovernmental Panel on Climate Change (IPCC), the trend of accelerating sea level rise in the Mediterranean is consistent [23]. However, there are important differences depending on the methods and time horizons used in the analyses. In general, the accepted sea level rise referred to in the 20 th century was 1.4 \(\pm\) 0.2 mm yr\({}^{-1}\)[24]. However, by 2050, it is estimated that the sea level may rise between 0.52 and 1.22 m above the mean relative sea level between 1996 and 2014. The relative sea level rise from 1927 to 2012 in Alicante was 1.28 \(\pm\) 0.5 mm yr\({}^{-1}\)[25]. This coastline has a long history of anthropogenic actions since the 18 th century. The dune system in this area was left unfixed due to the massive falling of trees for the fishing industry during the 18 th century. This meant that for a long time, the town of Guardamar was \"threatened\" by the movements of the dunes. From 1900 to 1930, the engineer [PERSON] directed the reforestation of the area, which reduced the mobility of the dunes and, therefore, prevented the burial of the town. The houses of Babilonia (zone C in Figure 1) did not respond to the predatory model of the urbanism of the second half of the last century around the Spanish Levante. On the contrary, they had an environmental function and fit perfectly with the coastal physiognomy of the municipality in the 1930s. The number of houses increased until the end of the 1970s and remained constant until the 2000s, but since then, houses started to naturally and progressively collapse due to marine action. See Figure 2 for some photographs of the area since 2010. The main period of anthropic actions began in the mid-1970s and lasted about 20/25 years.