People tend to respond to the threat of sea-level rise. Three broad response strategies can be distinguished: planned retreat, accommodation, and protection. In the latter strategy, land is maintained as it is now, albeit with a decline in natural functions and values. In the first strategy, coastal processes are allowed to occur naturally, but valuable developments are prevented or withdrawn in time. The strategy of accommodation is intermediate; the response in this case is to control the impacts of sea-level rise by changing land use. The strategy chosen depends on national circumstances, including the economic and ecological importance of the coastline, technical and financial capabilities, and the legislative and political structure of the countries concerned.
Because most low-lying coastal areas in Europe already are protected from flooding, a rise in sea level by itself will not cause serious inundation of human-occupied areas. Assuming other climatic factors remain constant, the protection offered by the flood defenses will decline as sea level rises, but its effectiveness will not disappear immediately (see, e.g., Kelly, 1991, for a discussion of the Thames Barrier, which protects London). Based on the GVA, the reduction in flood protection will be largest around the Mediterranean (Nicholls and Hoozemans, 1996). Anticipating accelerated sea-level rise in the design of new flood defenses will counter this effect (U.K. Department of the Environment, 1996).
Analysts often employ simplifying assumptions regarding response strategies. The costs in Table 5-4, for example, assume that all densely populated areas will be protected. An alternative assumption is that the costs of protection (including the monetary values of nature) will be balanced against the costs of land loss. Fankhauser (1994) analyzed this assumption for countries in the OECD. He concludes that it is optimal to protect all harbors and cities. Open coasts and beaches need to be maintained and protected in densely populated areas (such as The Netherlands) and in areas where beach tourism is important (such as Greece, Italy, and Spain). On the other hand, areas with low population density (such as Norway and Iceland) and poorer areas (such as Turkey) have a lower optimal level of protection. Turner et al. (1995) analyzed protection in East Anglia, England. At the regional scale, protection can be justified for the entire coast. When the 113 individual flood compartments were evaluated, however, the study indicated that it may not be economically justifiable to continue to protect 20% of compartments, even with modest rates of sea-level rise. This analysis assumes that there is no interaction between flood compartments-which may not always be the case. However, it suggests that a range of responses, rather than a single response, may be appropriate at regional and national scales.
Responses may be hindered by resource constraints. In Cyprus, the coast is almost totally sediment-starved as a result of catchment regulation and management (Nicholls and Hoozemans, 1996), and there are no ready sources of sand available for beach nourishment. Yet maintaining the beach is critical to the tourist industry. Therefore, external (and hence costly) sources of sand may be required for beach nourishment. Many other Mediterranean islands appear to have similar problems.
Some adaptation that anticipates climate change already is being implemented, despite the costs (U.K. Department of the Environment, 1996). In The Netherlands, national policies that outlaw erosion and mandate maintenance to the present shoreline position already are in place (Koster and Hillen, 1995). In the Ebro, Rhone, and Po deltas, conceptual and quantitative models of deltaic responses to sea-level rise are being developed (Jimenez and Sanchez-Arcilla, 1997; Sanchez-Arcilla and Jimenez, 1997). The ultimate goal of this work is to harness natural processes within deltas to counter global and local (due to subsidence) sea-level rise. However, other coastal settings often are not being managed with climate change in mind (Nicholls and Hoozemans, 1996). This approach often ignores numerous opportunities to use existing changes, such as the redevelopment cycle of coastal urban areas, to adapt to climate change (IPCC 1996, WG II, Chapter 9). Planning for and responding to sea-level rise raise important questions of equity, such as who pays for eroded land (if retreat is a response). These issues remain to be addressed systematically.
A more strategic and integrated perspective regarding coastal management and shoreline protection has been triggered by climate change, although resulting efforts have to consider more than just climate change. In Britain, guidelines for estuary management (English Nature, 1993) and shoreline management (U.K. Ministry of Agriculture, Fisheries and Food et al., 1995) have been published, and a number of shoreline management plans and estuary management plans have been completed or are being formulated. Recognition of sediment cells and the benefits of erosion and beach nourishment in terms of sediment supply to other parts of the cell are being more fully realized (Bray et al., 1996). The flood-prevention benefits of coastal wetlands also are being assessed. In eastern Britain, some managed setback schemes have been carried out on a pilot basis. In these areas-which had previously been reclaimed for agriculture-the sea defense has been realigned and the seawall breached to recreate areas of salt marsh and intertidal habitat. This strategy is expected to assist in the restoration of natural balance in estuaries and to provide flood alleviation benefits. It is anticipated that larger-scale application of such defense realignment, in appropriate locations, may be required to counter expected losses of intertidal habitat and relieve pressure on artificial defenses from sea-level rise. Such a policy may find more widespread application in Europe and would help minimize wetland losses resulting from sea-level rise.
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