Nat. Hazards Earth Syst. Sci., 17, 449–466, 2017 www.nat-hazards-earth-syst-sci.net/17/449/2017/ doi:10.5194/nhess-17-449-2017 © Author(s) 2017. CC Attribution 3.0 License. Assessment of island beach erosion due to sea level rise: the case of the Aegean archipelago (Eastern Mediterranean) Isavela N. Monioudi1, Adonis F. Velegrakis1, Antonis E. Chatzipavlis1, Anastasios Rigos1,2, Theophanis Karambas3, Michalis I. Vousdoukas4,1, Thomas Hasiotis1, Nikoletta Koukourouvli5, Pascal Peduzzi6, Eva Manoutsoglou1, Serafim E. Poulos7, and Michael B. Collins8 1Department of Marine Sciences, University of the Aegean, University Hill, 81100 Mytilene, Greece 2Department of Cultural Technology and Communication, University of the Aegean, University Hill, Mytilene 81100, Greece 3School of Civil Engineering, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece 4European Commission, Joint Research Centre (JRC), Directorate for Space, Security and Migration Disaster Risk Management Unit, Via E. Fermi 2749, 21027 Ispra (VA), Italy 5Department of Geography, University of the Aegean, University Hill, 81100 Mytilene, Greece 6UNEP/DEWA/GRID-Geneva, International Environment House, 11 Chemin des Anémones, 1219 Châtelaine, Switzerland 7Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, Panepistimioupoli Zografou, 15784 Athens, Greece 8Plentziako Itsas Estazioa, University of the Basque Country, Areatza z/g, 48620 Plentzia-Bizkaia, Spain Correspondence to: Michalis I. Vousdoukas ([email protected]) Received: 17 October 2016 – Discussion started: 7 November 2016 Revised: 17 January 2017 – Accepted: 4 February 2017 – Published: 21 March 2017 Abstract. The present contribution constitutes the first com- vulnerable to mean sea level rise (MSLR) and episodic SLRs prehensive attempt to (a) record the spatial characteristics due to (i) their narrow widths (about 59 % of the beaches of the beaches of the Aegean archipelago (Greece), a crit- have maximum widths < 20 m), (ii) their limited terrestrial ical resource for both the local and national economy, and sediment supply, (iii) the substantial coastal development (b) provide a rapid assessment of the impacts of the long- and (iv) the limited existing coastal protection. Modeling re- term and episodic sea level rise (SLR) under different scenar- sults indeed project severe impacts under mean and episodic ios. Spatial information and other attributes (e.g., presence of SLRs, which by 2100 could be devastating. For example, coastal protection works and backshore development) of the under MSLR of 0.5 m – representative concentration path- beaches of the 58 largest islands of the archipelago were ob- way (RCP) 4.5 of the Fifth Assessment Report (AR5) of tained on the basis of remote-sensed images available on the the Intergovernmental Panel on Climate change (IPCC) – a web. Ranges of SLR-induced beach retreats under different storm-induced sea level rise of 0.6 m is projected to result morphological, sedimentological and hydrodynamic forcing, in a complete erosion of between 31 and 88 % of all beaches and SLR scenarios were estimated using suitable ensembles (29–87 % of beaches are currently fronting coastal infrastruc- of cross-shore (1-D) morphodynamic models. These ranges, ture and assets), at least temporarily. Our results suggest a combined with empirically derived estimations of wave run- very considerable risk which will require significant effort, up induced flooding, were then compared with the recorded financial resources and policies/regulation in order to pro- maximum beach widths to provide ranges of retreat/erosion tect/maintain the critical economic resource of the Aegean and flooding at the archipelago scale. The spatial information archipelago. shows that the Aegean “pocket” beaches may be particularly Published by Copernicus Publications on behalf of the European Geosciences Union. 450 I. N. Monioudi et al.: Assessment of island beach erosion due to sea level rise 1 Introduction coastal infrastructure and assets and/or as significant envi- ronments of leisure (e.g., Paula et al., 2013). Therefore, as- Beaches are critical components of the coastal zone; not sessments of the beach morphological evolution at different only are they significant habitats in their own right (e.g., spatiotemporal scales are required based on advanced nu- Defeo and McLachlan, 2013), but they also provide protec- merical, analytical and/or empirical models constructed and tion from marine flooding to other transitional ecosystems applied by experienced operators and set up/validated using and the coastal assets, infrastructure and activities they front appropriate field data and backed by expert analysis (e.g., (e.g., Neumann et al., 2015). At the same time, tourism has Roelvink et al., 2009; Bosom and Jiménez, 2010; Ding et been increasingly associated with beach recreational activ- al., 2013). However, such efforts are usually hampered by ities according to the dominant “Sun, Sea and Sand - 3S the (a) scarcity of relevant information in many coastal areas tourism” model (Phillips and Jones, 2006). Consequently, and (b) dearth in the necessary human and financial resources beaches have become very important economic resources (e.g., Parker et al., 2013); this is particularly true when as- (Ghermandi and Nunes, 2013) forming one of the pillars of sessments of beach erosion are carried out over larger spatial tourism, an economic sector that contributes an estimated scales. Nevertheless, it is necessary to assess future beach re- 5 % of Gross Domestic Product (GDP), and about 6–7 % treat/erosion and flood risk at large spatial scales in order to of global employment (directly and indirectly) (Hall et al., identify “hot spots” and plan for effective adaptation policies 2013). and efficient allocation of resources. Beaches are also very dynamic environments, controlled Against this background, the objective of the present study by complex forcing-response processes that operate at var- is to assess the erosion and temporary inundation/flood risks ious spatiotemporal scales (Short and Jackson, 2013). They of the beaches of the Aegean archipelago islands (Greece) are generally under erosion (Eurosion, 2004; IPCC SREX, under different scenarios of sea level rise (SLR). Towards 2012; IPCC, 2013), which can be differentiated into (a) long- this objective, spatial characteristics such as the area, length, term erosion, i.e., irreversible retreat of the shoreline, due to maximum width, orientation, sediments and the presence of mean sea level rise (MSLR) and/or negative coastal sedimen- coastal works and backshore development of the Aegean tary budgets that force either beach landward migration or beaches were recorded. This information was then used in drowning (Nicholls and Cazenave, 2010), and (b) short-term conjunction with projections from ensembles of cross-shore erosion caused by storm surges and waves which, may or morphodynamic models to obtain estimates of the ranges of may not, result in permanent shoreline retreats but can be potential beach retreat/erosion and flooding under different nevertheless devastating (e.g., Smith and Katz, 2012; UN- MSLRs and storm conditions. ECE, 2013). The accelerating MSLR coupled with episodic storm events will aggravate the already significant beach ero- sion with severe impacts on coastal activities, infrastructure 2 Aegean archipelago beaches: significance, and assets (e.g., Jiménez et al., 2012), and the beach carry- environmental setting and sea level rise ing capacity for recreation/tourism (Valdemoro and Jiménez, 2006; McArthur, 2015). 2.1 Significance of the Aegean archipelago beaches Beach erosion appears to be particularly alarming in is- lands. Island beaches are increasingly vulnerable to erosion The Aegean archipelago (Fig. 1) consists of several thousand due to their (generally) limited dimensions and diminish- islands and rock islets with a combined area of 17 550 km2 ing sediment supply (e.g., Velegrakis et al., 2008; Peduzzi and a total coastline length of about 5880 km (Eurosion, et al., 2013). At the same time, island beaches are amongst 2004). Few of these islands and islets are populated; less the most significant 3S tourism destinations. For example, 3S than 70 islands have more than 100 permanent inhabitants tourism accounts for more than 23 % of the Gross Domestic and 45 have more than 1000 (http://www.statistics.gr/en/ Product in many Caribbean Small Island Developing States interactive-map). Yet Aegean islands form very significant and in some cases, e.g., Antigua and Barbuda, for more than tourist destinations. About 50 % of all Greek hotel beds (and 75 % (ECLAC, 2011). Mediterranean islands are also major > 60 % of all 5 star hotel beds) are located in the Aegean tourism destinations; in Greece, most of the hotel capacity archipelago, with 43 % of the foreign arrivals to Greece in and foreign tourist arrivals and earnings are associated with 2015 (7.4 out of a total of 17.1 million) arriving at its 11 in- the Greek islands (SETE, 2016). ternational airports (SETE, 2016). Under a variable and changing climate, projections on the In recent years, tourism has become a most signif- future evolution of beach morphology are not easy due to un- icant economic activity in Greece. In 2013, foreign certainties regarding both forcing and beach response (e.g., earnings of the Greek tourist industry were about Short and Jackson, 2013). Nevertheless, beach erosion is EUR 15.5 billion (http://www.bankofgreece.gr/Pages/el/