Risk assessment of oil spills along the Mediterranean coast: A sensitivity analysis of the choice of hazard quantification
Graphical abstract
Introduction
The Mediterranean basin extends over an area of 2.5 M km2 representing only 0.8% of the world's sea surface and 0.3% of its volume, but it is characterized with a heterogeneous typology and rich ecosystem that hosts ~ 8% of the world's biodiversity (WWF, 2015, UNEP-MAP, 2012, Coll et al., 2010, Bazairi et al., 2010, Olson and Dinerstein, 1998). It is considered an important hub for trade and is known to be one of the busiest waterways worldwide, encompassing 15% of the world's shipping activity and 10% of vessel deadweight tonnage with ~ 200,000 commercial ships passing through it annually (UNEP-MAP, 2012). As a result, the basin is considered highly vulnerable to pollution (Gürlük, 2009). Its vulnerability stems from its intrinsic physical characteristics and anthropogenic activities along its coastline, with the threat of oil spills being of particular concern due to the presence of offshore rigs, oil-related operations, and heavy oil traffic (Abdulla and Linden, 2008). These factors along with recent important oil and gas discoveries and production in the Levantine basin compel observance for oil spill hazards and risks along the Mediterranean. Whether they occur as a result of tanker accidents, rig explosions, loading/unloading incidents, storage leakage, or acts of war, oil spills represent a serious concern both environmentally, due to their adverse impacts on coastal ecosystems, and socio-economically, given their impacts on activities along the coastline.
In the event of an oil spill, its slick trajectory is of interest to direct available resources towards control and mitigation. The movement of the oil slick is simulated as a function of prevailing winds, currents, and wave conditions, while also accounting for the physical, chemical and biochemical processes affecting the oil (Olita et al., 2012). Mathematical modeling is often relied upon for this purpose to simulate the transport and weathering of oil once an accident occurs (El-Fadel et al., 2012, Darras, 1982, Baruque et al., 2010) or to better prepare emergency response plans in anticipation of a potential incident. Moreover, oil spill modeling is used both for hindcasting or forecasting purposes.
While oil spill modeling has historically focused on simulating the fate and transport of actual spills, either as part of an oil spill response (Berry et al., 2012, El-Fadel et al., 2012, Baruque et al., 2010, Wang et al., 2005, Al-Rabeh et al., 1992, Galt et al., 1991, Al-Rabeh et al., 1989, Darras, 1982) or as part of model validation (Chao et al., 2003, Elhakeem et al., 2007, French-McCay, 2004), the integration of oil spill modeling within national oil spill contingency plans has been gaining ground and is now considered as an essential tool in risk assessment procedures and emergency response planning (IPIECA, 2008, IPIECA-OGP, 2015a, IPIECA-OGP, 2015b, REMPEC, 2005, UNEP, 2005). Oil spill risk assessments aim to quantify the probability of damaging consequences following a spill over a certain period of time (Castanedo et al., 2009). Various methods have been developed to assess oil spill risks based on empirical and intuitive approaches while others are simulation-based (Stewart and Leschine, 1986).
This study adopts the second approach to examine the risks posed by potential oil spills along the Mediterranean coastline by quantifying the hazards associated with a spill and accounting for the sensitivity of the shoreline. Several hazard indices are developed including the probability of oil slick contact at a given shoreline, the average concentrations of oil stranding onto the shore, as well as the mean time of oil shoring. Differences in risk characterization between these metrics is then assessed and linked to geomorphological characteristics of the coastline. For this purpose, several scenarios covering a range of spill conditions, shorelines, and weathering conditions, were tested at four pilot areas to develop a new assimilative oil spill hazard metric for use along the Mediterranean coastline. The integration of the developed oil spill hazard metric within the existing Mediterranean-wide decision support system is also explored. Emphasis is placed on the opportunity to optimize response following an event with regards to resource deployment.
Section snippets
Study pilot areas
Within the framework of the European Union (EU) Great Med Project, four Mediterranean countries were considered in the analysis, namely France and Italy on the northern Mediterranean coastline, Lebanon on the Eastern coastline, and Tunisia on the southern coastline (Fig. 1). In each country, the coastal vulnerability and exposure to potential oil spills were assessed. In France, the Provence-Alpes-Côte d'Azur (PACA) region was chosen. It includes many protected sites, national parks and
Oil spill hazard quantification
In Marseille, the simulated number of hits, concentrations, and time to beach along the coastline are depicted in Fig. 2, Fig. 3. The hazard based on the number of hits proved to be highly correlated with the hazard quantified as a function of average yearly-beached oil concentrations, with a Pearson's correlation coefficient of 0.98 suggesting that shorelines likely to get hit by oil are also highly susceptible to receive high oil volumes. Correlations were also found between the time to shore
Conclusion
Potential oil spills at pilot areas along the northern, eastern, and southern Mediterranean were simulated using MEDSLIK II. Oil hazard was assessed using three different metrics: susceptibility of oiling per beach segment, the average volume of oiling expected in the event of beaching, and the average oil beaching time. The results indicate that while the three indices largely agreed when the shoreline morphology is simple, considerable differences in the quantification of hazards were
Acknowledgements
The GREAT Med project is financed by the European Union (ENPI CBC Mediterranean Sea Basin Programme) through the European Neighborhood and Partnership Instrument. Its Grant Agreement is no. 39/2377.
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