9.3.6. Coastal Systems

9.3.6.1. Sea-Level Rise and Coastal Changes

Major coastal impacts will result from accelerated sea-level rise; these effects will include coastal erosion, saline intrusion, and sea flooding, among other impacts. Impact studies have confirmed that low-lying deltaic and barrier coasts, low reef islands, and coral atolls are especially vulnerable to the potential impacts of sea-level rise (Maul, 1993). Some small islands could suffer land loss and experience increased beach erosion, inundation, and flooding from a sea-level rise of between 50 cm and 1 m. Leatherman (1994) suggests that sea-level rise could convert many islands in the Maldives to sandbars and significantly reduce available dry land on larger, more heavily populated islands. In Majuro Atoll (Marshall Islands), computation of land loss from a 1-m rise in sea level, based on the Bruun rule, suggests that approximately 60 ha of dry land (8.6% of the total land area) would be lost to erosion. It also is estimated that more than 115 ha of Majuro Atoll would be inundated if a 1-m sea-level rise were superimposed on present-day flooding from wave runup and overtopping (Holthus et al., 1992). In the case of Kiribati, Woodroffe and McLean (1992) have suggested that 12.5% of the total land area would be vulnerable with a 1-m rise in sea level.

Notwithstanding these projections, the response of islands to the impacts of climate change will vary within regions and even within countries. Islands are not passive systems; they will respond dynamically in variable and complex ways to sea-level and climate changes (Aalbersberg and Hay, 1993; McLean and d'Aubert, 1993; McLean and Woodroffe, 1993). For example, the extent to which relative sea-level rise will affect coastal recession rates will depend on many factors, including (though not limited to) the rate of sediment supply relative to submergence; the width of existing fringing reefs; the rate of reef growth; whether islands are anchored to emergent rock platforms; whether islands are composed primarily of sand or coral rubble; the presence or absence of natural shore-protection structures, such as beachrock or conglomerate outcrops; the presence or absence of biotic protection, such as mangroves or other strand vegetation; the health of coral reefs; and, especially, the tectonic history of the island.

9.3.7. Human Settlement

9.3.7.1. Infrastructure and Settlement

Generally, the largest concentrations of settlements on small islands occur no further than 1-2 km from the coast, and sometimes much less. In most of the eastern Caribbean states, for instance, more than 50% of the population resides within 2 km of the coast; the corresponding figure in Barbados is estimated to be in the region of 60% (Nurse, 1992). Similarly, large coastal populations are the norm in the Pacific and Indian Ocean islands-especially the atoll states, where settlement areas may even be sited on the beach itself or on the sand terrace (e.g., Tuvalu, Kiribati, Maldives). Clearly, such settlements are at risk from projected sea-level rise-which, in all likelihood, would be accompanied by inundation, increased flooding, coastal erosion, and consequently land loss.

On many small islands, critical infrastructure tends to be located in or near coastal areas; this infrastructure will be highly vulnerable to the effects of projected sea-level rise, especially during extreme events. Similarly, significant infrastructural damage could result from any increase in the frequency or intensity of extreme events such as floods, tropical storms, and storm surges (Pernetta, 1992; Alm et al., 1993). Moreover, because island populations tend to congregate in the few urban centers where most of the infrastructure and services are located, damage to important infrastructure (e.g., coastal roads, bridges, seawalls) would be disruptive to several types of economic, social, and cultural activities. In Malta, for example, vital desalinization facilities on the coast would be at risk in such circumstances (Sestini, 1992). Social and economic dislocation would be especially severe among communities with high population densities-such as Eauripik, Federated States of Micronesia (950 persons/km²); Majuro, Marshall Islands (2,188 persons/km²); and Male, Republic of Maldives (5,000 persons/km²).

The costs of protecting the shoreline and other infrastructure will vary, depending on the kind of protection needed, the length of area to be protected, design specifications to be adopted, and the availability of construction materials. There is concern, however, that the overall costs of infrastructure protection will be beyond the financial means of many island nations. Vulnerability studies conducted for selected small islands suggest that the costs of coastal protection ("hard" options) would be a significant proportion of GNP (see IPCC 1996, WG II, Table 9-3). In Malta and Cyprus, it is estimated that approximately US$550 million and US$190 million, respectively, would be needed to provide adequate shore protection works against a 20-30 cm rise in relative sea level (Sestini, 1992). Although these estimated costs might not be excessive in the context of large economies, they represent considerable financial resources that these small island states would have to reallocate.

The cost of insurance is another important factor that must be taken into consideration in any assessment of climate change impacts on infrastructure. Property insurance costs are extremely sensitive to the effects of catastrophic events such as hurricanes, floods, and earthquakes. High-risk locations therefore could face high insurance premiums-and even, in extreme cases, withdrawal of coverage (Box 9-3).

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