COASTAL DAMAGES CAUSED BY AN EXTREME STORM (GLORIA EVENT) ALONG THE SPANISH MEDITERRANEAN COAST Sancho-García* A., Guillén** J. and Rubio-Nicolás* B. *IMEDMAR-UCV (Universidad Católica de Valencia), [email protected] **Marine Sciences Institute (ICM-CSIC), [email protected] ABSTRACT An extreme storm event called Gloria hit the Spanish Mediterranean coast on the 18th-26th January 2020. The waves were generated by a low pressure system coming from the Atlantic Ocean and propagated with a mean wave direction of 55º. It was recorded a historical maximum of significant wave height of 8.4 m (Tp = 11.7 s) in the Gulf of Valencia and a sea level around 60 cm above the mean level. The storm caused a severe damage along the coast, with erosion and flooding of beaches and destruction of coastal infrastructures. In this work, we evaluate the distribution and intensity of coastal damages caused by this extreme event along the Spanish Mediterranean coast based on the analysis of published news in the most popular newspapers of each region. The type of damage, its intensity and spatial distribution are discussed. Most of the beaches were impacted by the storm, being the main damages the erosion and destruction, and the most impacted provinces Valencia, Castellón and Barcelona. This methodology is suggested to be a good approach to comparatively evaluate damages caused by extreme storms at a regional scale. Keyword: extreme waves, storm surge, coastal damages, Mediterranean Sea. 1. Introduction Coastal hazards caused by extreme storm events impact on infrastructure and economy, and also produce non-monetary issues as loss of human life or ecosystem services. During the last decades, there is an increase of coastal hazards impacts which is attributable to both the greater exposure of people and goods in the coast and to the climate change. For the 21st century, several global and regional studies have showed that predicted changes in atmospheric storminess may induce respective alterations to sea water levels (Androulidakis et al., 2015). Thus, an adequate assessment of damages caused by extreme events require to implement measures of mitigation and adaptation of the coastal zone. Facing the difficulties of the accurate estimation of damages at a regional scale, the use of news reported in local newspapers has demonstrated to be an adequate evaluation method (Ibsen and Brunsden,1996; Jiménez et al., 2012; Garnier et al., 2017). In this work, news reported in newspapers are used to evaluate damages in the Spanish Mediterranean coast during the passage of the extreme storm Gloria in January 2020. Gloria was a low-pressure system coming from the Atlantic and made landfall in the north-western part of the Iberian Peninsula on 17th January 2020. It evolved towards the southeast until reaching the Spanish Mediterranean Coast on 19th January. It was absorbed by a larger low-pressure system which was centred over the Alboran Sea and it lasted until 26 January (Amores et al., 2020). 2. Material and methods 2.1 Study area The study area comprises the regions of the Spanish Mediterranean Sea affected by the Storm Gloria: Catalonia (Girona, Barcelona and Tarragona), Valencian Community (Castellón, Valencia and Alicante) and Murcia Region from north to south along the Iberian Peninsula and the Balearic Islands (Mallorca) (Figure 1). It corresponds to a total coastline length of about 2100 km comprising a high diversity of coastal geomorphologies (from cliffs to deltas, embayed or urban beaches) and more than 1000 beaches (Table 1). This area is microtidal (range < 0.2 m) and waves are the main driving process during storms. Table 1. Coastline length (IGN, 2020) and number of beaches (MITECO, 2020) in each region Region Coastline length (km) Number of beaches Girona 104 260 Barcelona 100 161 Tarragona 127 278 Castellón 96 139 Valencia 69 135 Alicante 163 244 Mallorca 208 606 Murcia 195 274 2.2 Wave and sea-level data Wave and sea-level measurements from different buoys and tide gauges located along the Mediterranean Spanish coast were provided by Puertos del Estado (www.puertos.es) and Instituto Geográfico Nacional (www.ign.es) (Figure 1). For the characterisation of this storm event, the maximum significant wave height (Hs) and their associated peak period (Tp) and wave direction (), the storm duration (휏) and the sea level () were obtained. The wave height threshold used to estimate the storm duration was 1.5 m. The considered zero sea level at each site was the mean sea level provided by the tide-gauge station. In order to characterise the potential erosion and destruction of this event, the Dolan and Davis (1992) maximum Storm Power Index (SPImax), i.e. the energy content for the storm, and the maximum wave energy (E) were calculated. As the integrated and maximum power index are almost linearly proportional (Eichentopf et al., 2020), SPImax was used for simplicity. 푆푃퐼 = 퐻푠 ∙ 휏 (1) 퐸 = 퐻푠 ∙ 푇푝 (2) Figure 1. Study area: location of the buoys (red) and tide gauges (green). Image Landsat/Copernicus Google Earth 2020. For the estimation of the potential inundation and backshore accumulation, it was defined the inundation index (ID), as the sum of the run-up (R2%) and the measured sea level. In the run-up evaluation (Stockdon et al., 2006) the maximum significant wave height (Hsmax) and the associated peak period (Tpmax) were used to calculate the deep water significant wave wavelength (L0) and an average foreshore beach slope (βf ) of 0.1 was used. The value of the sea level was that corresponding to the maximum wave height (Hsmax) measured during the storm. 0.5 0.563훽 2+0.004 퐼퐷 =푅 +휂 = 1.10 ∙ (퐻푠 ∙퐿 )0.5 ∙ 0.35훽 + 푓 + 휂 (3) % 퐻푠푚푎푥 0 푓 2 퐻푠푚푎푥 2.3 Storm-induced damages A systematic analysis of the news published from 18 January to 31 March 2020 in the most relevant newspapers of each region (Table 2) was carried out to characterise the storm- induced damages. Images of the damages produced by the event Gloria on the beaches and in the infrastructures (mainly beach promenades) were included on the frontpage of all the newspapers. The number of the news published during the period varied between the newspapers, being Levante-EMV which reported the large amount of news (30). Table 2. Newspapers used in this study Region Newspaper Source Catalonia (Girona, La Vanguardia https://www.lavanguardia.com/hemeroteca Barcelona, Tarragona) Valencia (Castellón, Levante -EMV https://www.levante- Valencia, Alicante) emv.com/servicios/html/hemeroteca.html Murcia La Verdad https://www.laverdad.es/hemeroteca/ Mallorca Island Diario de https://www.diariodemallorca.es/servicios/html/hemeroteca. Mallorca html The following information was collected for each news: date, location (beach, municipality, region) and type and extent of the damage. The type of damage was classified in four classes: destruction (damage to infrastructures such as beach promenade or beach furniture), erosion, inundation and sand accumulation and their intensity on a three-class scale (maximum, medium and low) according to Jiménez et al. (2012). Besides, as damages are reported in the news differently (sometimes the damage is described to a specific location and others from a wider region), it was applied an accuracy index as defined by Gracia et al. (2015) in order to weight the importance of each damage. Thus, if the news refers to a specific site the accuracy index was 3, to the municipality 2 and to the region (province) the assigned value was 1. Finally, to compare the regional variability, the total damage was weighted by the number of beaches for each region. The same procedure was followed for each typology of damage. 3. Results and discussion 3.1 Wave power and storm surge during the Gloria event The wave characteristics during the storm Gloria are presented in Table 3 and in Figure 2. In general, wave conditions during the storm showed a fast increase of the wave height and period until the peak and later a slower decrease of storm conditions. The wave direction was from the NE in all the sites. The significant wave height recorded at the peak of the storm was higher than 7.6 m in all the sites (except in the Cabo de Palos buoy) and the mean duration of this event was 115 hours. The maximum significant wave height was measured at the Valencia buoy (8.4 m), which was the highest ever measured in this buoy. All buoys, except Mahón and Cabo de Palos reached historic significant wave heights. 2 The associated SPImax ranged from 4,000 to 8,000 m ·h and the wave energy from 400 to 800 m2·s. The maximum wave energy during the peak of the storm corresponds to the Valencia site and the highest SPImax to Mahón and Begur sites, where the duration of the storm was longer. Table 3. Wave characteristics (maximum significant wave height and the associated peak period and wave direction and the duration), maximum Storm Power Index (SPImax) and wave energy (E) during the peak of the Gloria event measured in different buoys of the Puertos del Estado network (Barcelona buoy stopped to register at the beginning of the peak of the storm and the data is not included). Wave Hsmax Tp Hmax Duration SPImax E Buoy directionHmax Coastline (m) (s) (h) (m2·h) (m2·s) (º) Begur 7.8 12.5 67 124 7544 760 Girona Tarragona 7.6 11.9 78 123 7104 687 Tarragona/Castellón Valencia/North of Valencia 8.4 11.7 55 95 6703 825 Alicante (Cabo la Nao) Cabo de South of 6 11.7 26 114 4104 Palos 761 Alicante/Murcia Dragonera 8 11.9 27 109 6976 Mallorca (W) (Mallorca) 756 Mahón 8 12.3 90 127 8067 787 Mallorca (E) Table 4 shows the maximum sea level measured during the storm and the sea level that occurred simultaneously with the maximum wave height along measurement stations.