Letras

First order draft (10.09.2005): do not cite or quote. Expertise for WBGU on Oceans and Global Change

Sea Level Rise: Coastal Impacts and Responses
Nick Brooks, Robert Nicholls, Jim Hall
Introduction In the 1990s it was estimated that 21 and 37 per cent of the global population lived within 30 km and 100 km, respectively, of the coast (Cohen et al. 1997; Gommes et al. 1997). Many large citiesare situated near or on coastlines, and a large proportion of global economic productivity derives from coastal areas (Turner et al., 1996). Trends towards urbanisation are likely to increase population densities in low-lying coastal areas; the population living within 30 km of the coast is growing at twice the global average and GDP growth in coastal areas exceeds the national average in manycountries (Bijlsma et al., 1996; Nicholls et al., 1999). Coastal zones are therefore of great importance as zones of settlement and play a vital role in the economic well-being of many nations. Sea level rise (SLR) will have profound implications for many coastal populations and the systems on which they depend. The consequences of SLR for a given population in a particular locality will depend onthe following factors: • • • • the amount of SLR locally the effects of this SLR on hazards such as storm surges the physical exposure of the population and associated systems to the immediate impacts of SLR and related coastal hazards the ability of the population and related systems to cope with these impacts.

Here we address the impacts of SLR using a risk framework, in which the risk to asystem is a function of the nature of the hazards faced by that system and the vulnerability of the system to the impacts of those hazards (Brooks, 2003; Brooks and Adger, 2005). A system may be an ecosystem, human population, settlement or geographic region, or other system or unit. Risk may be measured in terms of the likelihood of a particular outcome (for example of economic losses above acertain threshold), or the losses accruing over a particular period (for example financial losses, area of land lost, or people killed). For coastal systems vulnerability is heavily influenced by physical exposure, particularly in terms of elevation above mean sea level, distance from the shoreline, and the presence of coastal defences or natural barriers such as wetlands, coral reefs or mangroveswhich can dissipate the energy of hazards such as storm surges. However, such natural barriers will provide little defence against long-term SLR. Vulnerability will also depend on the resilience of systems to the immediate impacts of coastal hazards, for example the quality of physical infrastructure, the preparedness of communities, and the ability of a system to recover from damage associated withcoastal hazards. Recovery will be aided by the availability of financial and other resources. In the longer term, vulnerability will depend on the ability of 1

First order draft (10.09.2005): do not cite or quote. systems to adapt to evolving hazards; this “adaptive capacity” will depend on a number of factors including the availability of resources, the availability of information on thelikely evolution of coastal hazards, and the availability and cost of technology that may assist in adaptation. This paper addresses each of the above issues at the global level, with examples from specific regions and locations where appropriate. The paper is divided into two parts, with the first section addressing the potential physical impacts of SLR on coastal areas. Issues of exposure areaddressed first, based on a number of plausible SLR projections for the next millennium. Sea levels will continue to rise for many centuries, even if atmospheric greenhouse gas concentrations (which are likely to remain the principal driver of SLR for the foreseeable future) are stabilised at relatively low levels (Wigley, 2005). A millennial timescale is therefore appropriate for studies of the...