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The Mediterranean region under climate change

 | 
Jean-Paul Moatti
, 
Stéphane Thiébault

Part 2. Vulnerability and impacts

Sub-chapter 2.2.2. Vulnerability of the Mediterranean coastal zones faced with the risk of climate change

Maria Snoussi et Alessio Satta

Texte intégral

Introduction

1Coastal communities and assets have been repeatedly threatened by the unpredictable sea conditions. Scientific evidence suggests that more intense storm surges and accelerated sea-level rise, related to climate change, are serious global threats for coastal areas and human society (IPCC, 2012). In the Mediterranean region, where nearly 40% of the coastline is built up and given the effects of future human encroachment on the coast, local authorities are faced with the increasingly complex task of balancing development and managing coastal risks, especially coastal erosion and flooding. Investigating the role of climate and non-climate drivers on coastal zones is therefore crucial to understand the underlying risks and identify appropriate and cost efficient response measures.

2According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2014), the risk of climate related impacts results from the interaction of climate related hazards with the vulnerability and exposure of human and natural systems, and changes in both the climate system and socio-economic processes are the key drivers of vulnerability, exposure and hazards. In this context, a comprehensive approach, based on a multi-risk method (Torresan et al. 2012; Satta et al. 2015; Gallina et al. 2016), is the most valuable tool that can be directly applied in coastal development programs in both the short and long term, and can assist decision makers in the implementation of preventive management strategies in the most sensitive areas. However, assessing current and future vulnerabilities and risks to coastal hazards is a challenge for both researchers and policy makers. It is important to understand that the assessments remain inherently uncertain, as they are derived from a process necessarily involving assumptions about a number of key factors, based on best available projections and expert knowledge (Markandya et al. 2016).

Multi-scale coastal risk assessment for the Mediterranean

3Satta et al. (2015) developed and applied a multi-scale coastal risk index, whose application at the regional scale (the Mediterranean basin) was called CRI-MED. This index has several advantages that make it particularly suitable to support decision making despite scarce resources, limited local data (especially along some of the southern and eastern shores of the Mediterranean) and uncertain information about the future. The CRI-MED is composed of three sub-indexes:

  1. Coastal forcing, characterizing the variables related to climate hazards (storms, drought, sea-level rise) and non-climate forcing (population growth, the number of tourists);
  2. Coastal vulnerability, integrating the resilience variables (age of the population, level of education) and coastal vulnerability variables (landform, elevation);
  3. Coastal exposure, describing coastal locations potentially at risk, the exposure (land cover, population density).

4The selected variables contribute in different ways to the risks affecting Mediterranean coastal zones and must be weighted accordingly for accurate calculation of CRI-MED. For the purposes of this study, sea level rise, storminess, as well as landform and elevation of coasts are considered to play the most significant roles in generating coastal risk.

5The CRI-MED spatial index combines multiple variable layers, representing different aspects of risk, in sub-indexes (vulnerability, forcing and exposure) layers, in such a way that risk hot-spots as well as areas of relatively lower risk emerge from the integration of the layers (Satta et al. 2015). The values for each variable, represented by a layer, are normalized to a consistent ordinal or unitless scale. The scaled layers are then averaged or summed to come up with a score referring to its contribution to coastal risk. The application of the CRI-MED to 11 Mediterranean countries selected for the ClimVar project led to ranking of the relative risk of each coastal region in relation to potential coastal hazards (coastal erosion, coastal flooding and saltwater intrusion) generated and/or exacerbated by climate forcing combined with human-induced forcing. The resulting risk map (Figure 1) represents the visualization and prioritization of risk in the coastal zones of the countries involved in the study. The final risk rankings are dimensionless numbers that judge the relative degree of risk of coastal zones to each coastal hazard analyzed, related to qualitative risk classes (i.e. extremely high, high, medium, low, extremely low). In this sense, higher risk values do not imply high risk in absolute terms, but only compared to other case coastal zones.

Figure 1
Coastal risk map of 11 Mediterranean countries (Satta et al., 2015).

6The CRI-MED therefore makes it possible to list the coastal hot-spots identified in each country. Coastal areas at extremely high risk are mainly located in the southern Mediterranean region; the countries concerned by coastal hot-spots include Morocco, Algeria, Libya, Egypt, Palestine, and Syria. Other countries in the region have areas at high risk (colored orange on the map), for instance in Albania and other Adriatic coastal sites. Finally, as per methodological assumptions, the hot-spot threshold was set in a way to highlight only areas that appear exceptionally at risk according to the statistical distribution of cells, where areas at high risk are located next to areas that are also at high risk.

Multi-scale coastal risk at the local scale (CRI-LS): the case of Tetouan coastline (Morocco)

7The local spatial scale application of the multi-scale coastal risk index methodology is called CRI-LS and it differs in some respects from CRI-MED. The main differences concern the need to define the coastal hazard zone at the local scale. The coastal hazard zone is the zone affected by the occurrence of the hazard, which may cause damage to, or loss of, natural ecosystems, buildings, and infrastructure. Concerning this point, Article 8 of the ICZM protocol specifically provides the definition of setback areas for the Mediterranean coastal regions, considered as the landward limit of the buffer zone behind the coastline, beyond which the acceptable level of risk produced by coastal hazard is defined (Satta et al. 2015). As the main hazards that act as forcing in the Mediterranean region are erosion and flooding (Satta et al., 2016), the overall hazard zone results from the overlaying of the erosion hazard zone and the flooding hazard zone. Higher resolution is required at the local than at the regional scale. In fact, in order to obtain more detailed information to plan appropriate strategies, several more variables are introduced for the three sub-indexes of vulnerability and exposure at the local scale.

8The first phase of the CRI-LS method consists in defining the coastal hazard zone, which results from the overlaying of the erosion hazard zone and the flooding hazard zone. Nineteen variables are proposed to describe the hazard, vulnerability and exposure sub-indexes (Table 1). The scores corresponding to each variable are calculated and the weights assigned using expert knowledge. The resulting values are hosted on a geographic information system (GIS) platform that enables the individual variables and aggregated risk scores to be color coded and mapped across the coastal hazard zone.

Table 1. CRI-LS variables

Coastal hazard sub-index

Coastal vulnerability sub-index

Coastal exposure sub-index

Sea level rise

Landform

Land cover

Storms

Coastal slope

Population density

Mean annual max daily precipitation

Land roughness

Drought events

Historical shoreline change

Population growth

Elevation

No of tourists

Distance from the shoreline

River flow regulation

Ecosystem health

Education level

Age of population

Coastal protection structures

9Tetouan is one of the coastal areas identified as a hot-spot in the CRI-MED assessment (Satta et al. 2015). Indeed, the coastline has been evolving in a sediment-deficit context (due to damming of rivers and overexploitation of sand dunes) for the last two decades. In addition, it has been subjected to increasing human pressure, including the construction of residential buildings on the foredunes and on vulnerable low lying coasts, construction of leisure ports (M’diq, Smir Marina and Kabila) and a road network along the coast. Over 95% of the coastal dunes have been destroyed by housing and tourism infrastructure. These coastal developments have seriously disturbed cross shore sediment transport and/or interrupted sediment transport along the shore, leading to a severe coastal erosion. Like for the definition of the coastal erosion and flooding, the worst SLR and extreme wave conditions (100 year return period) scenarios to 2100 were used. The application of the CRI-LS to the coastal hazard defined for Tetouan led to the ranking of the values of forcing, vulnerability and exposure illustrated in figure 2.

Figure 2
Coastal forcing (a), Coastal vulnerability (b), Coastal exposure (c).

10Figure 2b shows that respectively 10% and 27% of coastline investigated are classified as very highly and highly vulnerable because of the combination of high erosion rates with high capital land use. The risk scores were obtained by multiplying the scores obtained by three sub-indices. In contrast to the CRI-MED index, here, higher risk values imply high risk in absolute terms and the proposed CRI-LS method makes it possible to rank the risk at the local scale of the study area. The risk map (figure 3) identifies areas within the coastal hazard zone with a relatively higher risk of climate related hazards. The risk map shows that some areas, especially the coastal plains, at distances of more than 5 km from the coast, are characterized by high levels of risk due to the low topography of the flood plains and to the high exposure values.

Figure 3
Coastal risk index.

11For direct application in policies, the CRI-LS provides the definition of the coastal hazard zone under the 2100 scenario, and a set of risk maps to assist policy makers in prioritizing coastal management efforts that need to be undertaken to minimize risks or mitigate the consequences of climate and non-climate related hazards. This tool can be easily incorporated in overall coastal management and adaptation strategies to support the implementation of the integrated coastal zone management (ICZM) Protocol.

Conclusion

12Multi scale risk assessment of Mediterranean coastal zones revealed many hot-spots along the southern and eastern shores, mainly associated with urban low-lying centers that are under multiples pressures from land use patterns and practices. In both the short and medium term, Mediterranean Sea coasts will probably experience greater stresses produced by non-climatic factors such as population growth, intensification of tourism, poor land and water management, resource overexploitation, urbanization, and the development of coastal infrastructure. Climate change and related impacts are expected to be more severe in the southern and eastern parts of the Mediterranean basin, the adaptability of which is generally limited by weaker economic and institutional conditions as well as by poorer availability of financial and technological resources. A feature of the Mediterranean is the commitment of the multilateral community and its institutional structures to resolve problems by taking action, including regulation and legal instruments, policy and planning initiatives, capacity building and public participation mechanisms.

13From the methodological point of view, the clear advantage of the multi-scale index is the choice of the balance between an overview and a detailed view. Users can chose the trade-off that is appropriate to their needs by selecting the most suitable index scale for the desired scale of management. The application of the MS-CRI at two different scales (CRI-MED and CRI-LS) emphasized that spatial scale is also an important aspect to take into account in the development of coastal vulnerability indices. No single scale is suitable for all needs. Different scales tend to reflect different priorities, and the influence of a given variable will increase or decrease as the scale changes (Satta et al. 2015). Multi-scale indices, like those presented here, can be used to assist coastal policy makers at different scales and scopes of application. Nevertheless, major differences exist between the regional and the local level (Satta et al. 2015). With CRI-MED, detail is sacrificed in order to gain an overview of the risk faced by the whole Mediterranean coastline, whereas, with CRI-LS, the level of detail is high but there is no real overview. It is up to the coastal manager or policy maker to determine the most appropriate scale or scales of index to apply, depending on whether the policy is national, regional or local. In an ideal world, indices would be based on local-level information that is aggregated and simplified as larger scales are considered. However, in terms of data availability, storage and processing, this is rarely feasible, given the time needed to undertake such risk assessment. Possible further developments could include creating an initial database of relevant methods and tools for risk and vulnerability assessment in the Mediterranean.

Acknowledgements

14The results presented in this chapter were achieved in the framework of the ‘‘Strengthening the Knowledge Base on Regional Climate Variability and Change” project prepared by Acclimatise and its associates. This project was funded by the GEF in the framework of the ClimVar project and implemented by Plan Bleu, Regional Activity Centre of the UNEP-MAP.

Bibliographie

References

Gallina V., Torresan S., Critto A., Sperotto A., Glade T., Marcomini A. (2016)
A review of multi-risk methodologies for natural hazards: Consequences and challenges for a climate change impact assessment. Journal of Environmental Management 168 (2016) 123-132.

IPCC (2012)
Managing the risks of extreme events and disasters to Advance climate change adaptation. A special report of working groups I and II of the intergovernmental Panel on climate change. In: Field, C.B., Barros, V., Stocker, T.F., Qin, D., Dokken, D.J., Ebi, K.L., Mastrandrea, M.D., Mach, K.J., Plattner, G.-K., Allen, S.K., Tignor, M., Midgley, P.M. (Eds.), Cambridge University Press, Cambridge, UK, and New York, NY, USA, p. 582

IPCC (2014)
Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1132 pp.

Markandya A., Dale N., Vafeidis A., Hinkel J., Lincke D., Wolff C. (2016)
Assessing the Socio-Economic Impacts and Adaptation Options for Climate Variability and Change in Mediterranean Coastal Zones. UNEP/PAP/RAC Report, Split, 67p.

Satta, A., Venturini, S., Puddu, M.,
Firth, J., Lafitte, A., (2015) Application of a Multi-Scale Coastal Risk Index at Regional and Local Scale in the Mediterranean. Plan Bleu Technical Report-September 2015.

Satta A., Snoussi M., Puddu M., Flayou L., Hout R. (2016)
An Index-based method to assess risks of climate-related hazards in coastal zones: the case of Tetouan. Estuarine, Coastal and Shelf Science, doi: 10.1016/j. ecss. 2016.03.021

Torresan, S., Critto, A., Rizzi, J., and Marcomini, A. (2012)
Assessment of coastal vulnerability to climate change hazards at the regional scale: the case study of the North Adriatic Sea, Nat. Hazards Earth Syst. Sci., 12, 2347-2368.

Table des illustrations

Légende Figure 1Coastal risk map of 11 Mediterranean countries (Satta et al., 2015).
URL http://books.openedition.org/irdeditions/docannexe/image/23463/img-1.jpg
Fichier image/jpeg, 157k
Légende Figure 2Coastal forcing (a), Coastal vulnerability (b), Coastal exposure (c).
URL http://books.openedition.org/irdeditions/docannexe/image/23463/img-2.jpg
Fichier image/jpeg, 225k
Légende Figure 3Coastal risk index.
URL http://books.openedition.org/irdeditions/docannexe/image/23463/img-3.jpg
Fichier image/jpeg, 105k

Auteurs

University Mohamed V, Morocco
Coastal Geoscientist, University Mohamed V, Faculty of Sciences, Department of Earth Sciences, Rabat, Morocco
ma.snoussi@gmail.com

University of Cagliari, Italy
Coastal geoscientist, Chief researcher climate change adaptation and coastal management The Mediterranean Sea and Coast Foundation - MEDSEA
alessiosatta@medseafoundation.org

© IRD Éditions, 2016

Conditions d’utilisation : http://www.openedition.org/6540