*4.6. Illustrative Wave Storm Event with Severe Impacts*

With the aim of characterizing in more detail wind and wave conditions during storm events on the southern edge of Tenerife, the variability of wind and wave conditions during the selected extreme events has been examined considering the evolution of wind speed and direction, as well as wave height, period, and direction. Furthermore, mean water wave elevation data measured at the tidal gauge north of GC (TG) have been used to explore the contribution of this phenomenon to the impacts of selected extreme wave storms. Although the analysis was carried out for each of the storms identified south of Tenerife, the evolution of the parameters during one selected storm is briefly described below as an example. The selection of this storm has been made on the basis of several storm characteristics (storm energy, maximum value of *Hm*<sup>0</sup> during the event, storm duration, wave direction during the storm) and the existence of evidence of its impact on tourist beaches extracted from the local press historical archives.

The selected storm occurred during late February and early March 2018, and it has been selected principally because of its significantly long duration (around 90 h). The maximum significant wave height during the storm was 4.1 m and the associated return period 12.3 years. This storm, named Emma, began to develop around 23 and 24 February to the NW of the Canary Islands, and progressively increased in intensity to reach its maximum between 26 February and 01 March, while it remained more or less stationary over the archipelago. Then, it continued its trajectory towards Northern Europe, progressively moving away from the islands. This low-pressure system resulted in strong winds blowing from the W-SW sector towards the islands and generating a wave storm that affected almost all the islands and, in particular, the southern and southwestern areas of Tenerife, with a large impact on the tourist beaches located on this coastal stretch.

Figure 10 shows the wave storm evolution as observed at point IP2. Figure 10c shows that before 23 February, the wind direction presents a remarkable variability, until 23 February, when it was established in the S-SW sector, as with the wave direction. On the other hand, Figure 10a reveals a rather positive relationship between the temporal evolutions of wind speed and wave height, indicating that it was a locally generated wave storm. This is also evidenced in Figure 10b, in which it can be seen that both the average and peak periods adopt quite low values during the episode. Finally, in Figure 10d, it can be seen that the storm's peak coincided with a fairly large high tide, with a tidal range of around 2 m. Regarding the effect of tidal level on the wave storm impacts, the evaluation of tidal ranges coincident with the timing of storm occurrence, during the period when tidal information is available (1992–2020), reveals that the tidal range during the storms identified as damaging events was, in all cases, higher than the average value (1.5 m), pointing out the well-known significant contribution of this factor to the impact of wave storms on the coastline. In this particular example, the combination of both phenomena caused important negative impacts, including damage to coastal structures and buildings near the coastline, as well as erosion problems on the beaches of Arona (Southwestern Tenerife), which were reported by the local press, such as observed in Figure 11, which shows the lack of sand and the severe damage caused on the promenade of Los Tarajeles beach, in Los Cristianos (Arona), which had to be closed during the period of their repair. Furthermore, the "Francisco Andrade Fumero" promenade, on Las Américas beach, was closed to public use due to flooding and damage. During the stormy period, the red flag was present on all the beaches of the highly tourism-dependent municipality of Arona.

**Figure 10.** Significant wave height, wind speed (**a**), mean and peak periods (**b**), wind and wave directions (**c**), *Hm*0, and mean water level (**d**) evolution at point IP2 during a severe storm affecting southern strips of Tenerife island.

**Figure 11.** Photograph illustrating the effects of the storm Emma on Los Tarajales beach and promenade, municipality of Arona, Tenerife (Diario de Avisos, 4 March 2018).
