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. In general, water level increases towards the southwest from Barcelona to Gandia, and decreases between Gandia and Alicante. The water level was comparatively low in the Balearic Islands tide gauges (Table 4 and Figure 3).

Run-up estimations reached several meters along the coast during the peak of the storm and the combination of run-up and storm surge surpassed 4 m from Girona to North of Alicante areas (Table 5). Therefore, flooding of the beaches was generalised along the coast.

Table 4. Maximum sea level measured at each tide gauge (max) and sea level associated to the maximum

wave height (Hmax).  Coastline Tide gauge max (m) Hsmax (m) Barcelona2 0.23 0.07 Barcelona Tarragona 0.41 0.28 Tarragona/Castellón Valencia3 0.57 0.37 Valencia Gandia 0.62 0.55 Gandia/North of Alicante (Cabo la Nao) Alicante 0.52 0.34 Alicante Murcia 0.33 0.08 Murcia Palma de Mallorca (W) 0.02 Mallorca 0.11 Alcudia 0.15 - Mallorca (E)

Table 5. Runup (R2%) and inundation index (ID) along the Spanish Mediterranean coast affected by Gloria. Barcelona is not included as the buoy stopped to measure during the peak of the event. Coastline R2% (m) ID (m) Girona 4.03 - Tarragona/Castellón 3.79 4.06 Valencia 3.91 4.28 Gandia/North of Alicante (Cabo la Nao) 3.91 4.47 Alicante (South) 3.31 3.64 Murcia 3.31 3.39 Mallorca (W) 3.89 3.90 Mallorca (E) 4.01 -

Figure 2. Time series of the wave height (Hs), peak period (Tp) and wave direction () during the storm event Gloria.

Figure 3. Time series of the water level during Gloria event at the different sites.

3.2 Comparison with the previous extreme storm In order to evaluate the singularity of the Gloria event, wave conditions are compared with that of the former extreme and regional storm event occurred on 21 January 2017. The wave characteristics, the SPImax and the wave energy E during the peak of the storm are shown in Table 6. Comparing to Gloria wave characteristics (Table 3), the January 2017 event had longer duration (more than 300 hours in some stations), although the maximum wave height (6.7 m) and period (10.7 s) were lower. Consequently, this event exhibited a higher SPI max but a lower wave energy during the peak of the storm than the Gloria event.

Table 6. Wave characteristics (maximum significant wave height and the associated peak period and wave direction and the duration), maximum SPI and wave energy during the peak of the storm on 21/01/2017 measured in different buoys of the Puertos del Estado network. Tp Wave Hsmax Duration SPImax E Buoy Hmax directionHmax Coastline (m) (h) (m2·h) (m2·s) (s) (º) Begur 6.4 10.2 77 321 13148 418 Girona Barcelona 5.2 10.6 104 137 3704 287 Barcelona Tarragona 6.2 10.5 74 229 8803 404 Tarragona/Castellón Valencia/North of Alicante Valencia 6.6 10.6 51 227 9888 462 (Cabo la Nao) Cabo de 6.6 9.5 30 196 8538 414 South of Alicante/Murcia Palos Dragonera 6.3 10.7 28 305 12105 425 Mallorca (W) (mallorca) Mahón 6.5 10.7 55 - - - Mallorca (E)

3.3 Storm-induced damages The inventory of beach damages reported in newspapers shows that 100% of the beaches of Castellón were to some extent damaged, followed by Valencia (97%), Barcelona (64%), Murcia (48%), Mallorca (36%) and Tarragona (20%).

The regional variability of storm Gloria induced damages along the Spanish Mediterranean coast is presented in Figure 4. The main reported damages were erosion and destruction. The Valencia area was the most severely impacted, followed by Castellón and Barcelona. However, it has to be highlighted that any obvious correlation between the damage intensity and wave/storm surge conditions is observed and differences in damage intensity are larger than wave/sea level regional changes. For instance, although Valencia was the most impacted area and with the maximum erosion damage, this area does not correspond to the maximum SPI but with highest wave energy during the storm.

Figure 4. Regional distribution of the damage (weighted by the number of beaches) caused by Gloria event

Focusing on the inundation, Girona and Valencia regions reached the highest values, that correspond with the maximum runup and inundation index (¡Error! No se encuentra el origen de la referencia.). As the methodology focuses on damages of beaches, inundation results for Tarragona region are underestimated because an extreme coastal flooding of 3 km inland in the Cape Tortosa and La Marquesa Beach areas occurred in the Ebro Delta (Copernicus Emergency Management Service, 2020) and an overwash of the Trabucador Bar remained for several weeks. Additional potential bias still unsolved in the data are the different perception/interest of the newspapers to these news (four different newspapers were analysed) or some over information around the biggest cities of these newspapers (as Barcelona and Valencia). Finally, it should be pointed out that damages caused in beaches by extreme storms largely depend of the beach characteristics (morphology, orientation, sediment,…) that are not included in the analysis. This fact can explain that the damage intensity and storm conditions are almost uncorrelated in the different study areas. In spite of these difficulties, results from this study show the large general impact of the storm Gloria along the Spanish Mediterranean coast, probably with an unprecedented regional extension, and provide the basis to establish a comparative analysis of the impact of extreme storms in this coast at a regional scale.

4. Conclusions The extreme storm Gloria impacted the Spanish Mediterranean coast from 18 to 26 January 2020. The storm severely impacted the coast and the damages caused a deep concern in society. As a ‘fast response’ actuation, we evaluated the damages caused by the Gloria storm based on news published in regional newspapers.

Wave direction was from the NE in all the sites and the mean duration of this event was 115 hours. The significant wave height reached unprecedented values in several stations (8.4 m in the Gulf of Valencia) and the storm surge reached more than 0.6 m at several sites. The comparison of wave conditions during Gloria with that of the former extreme storm event occurred on 21 January 2017 indicates that Gloria had higher values of wave energy but lower SPImax values because of the differences in storm duration. Consequently, in terms of wave energy, storm Gloria probably reached unprecedented records on a regional scale.

The regional distribution of damages shows the impact of Gloria in the majority of the beaches, erosion and destruction being the main reported damages. The most impacted provinces were Valencia (the zone with the maximum wave energy), Castellón and Barcelona. In general, the regional distribution of SPImax values is uncorrelated to the distribution of damages, in particular in the Valencia area, because the effect of beach characteristics is not included in the analysis. However, although some bias can affect the data obtained from the news, it has been characterised the damages and the extension of Gloria event impact along the Spanish Mediterranean coast and this approach can provide the basis to establish a comparative analysis of the impact of the past and future extreme storms in this coast at a regional scale.

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6. ACKNOWLEDGEMENTS This work has been done in the framework of the MOCCA research project (RTI2018-093941-B-C32) funded by the Spanish Ministry of Science, Innovation and Universities – National Agency of Research. We thank Puertos del Estado (Spanish Ministry of Public Works) and Instituto Geográfico Nacional (IGN, Ministry of Development), in particular a Mª Ángeles Fraile, for supplying wave data and water levels used in this study. We also want to thank to the newspapers that provide the data: La Vanguardia, El Levante, Diario de Mallorca and La Verdad.