|Working Group II: Impacts, Adaptation and Vulnerability|
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22.214.171.124. Coastal Zones
Coastal zones in Europe contain large human populations and significant socioeconomic activity. They also support diverse ecosystems that provide significant habitats and sources of food. Significant inhabited coastal areas in countries such as The Netherlands, England, Denmark, Germany, Italy, and Poland already are below normal high-tide levels, and more extensive areas are vulnerable to flooding from storm surges. Hard defenses to prevent such flooding, combined with the loss of the seaward edge of coastal habitats as a result of existing rates of sea-level rise, already are causing significant coastal squeeze in many locations (e.g., Pye and French, 1993; Rigg et al., 1997; Lee, 1998). Deltaic areas often are particularly threatened because they naturally subside and may have been sediment-starved by dam construction (e.g., Sanchez-Arcilla et al., 1998). Other nonclimate change factors such as pollution may condition the impacts of climate change. Information further to the summary given below appears in the chapter on coasts in the European ACACIA report (Nicholls, 2000).
Climate change could cause important impacts on coastal zones, particularly via sea-level rise and changes in the frequency and/or intensity of extreme events such as storms and associated surges. Under the SRES climate change scenarios, global sea level is expected to rise by 13–68 cm by the 2050s. Regional and local sea-level rise in Europe generally will differ from the global average because of vertical land movements (glacial isostatic rebound, tectonic activity, and subsidence). Deviations from the global mean sea level also will occur as a result of oceanic effects such as changes in oceanic circulation, water density, or wind and pressure patterns. Mediterranean sea levels have fallen by as much as 20 mm relative to the Atlantic since 1960, probably as a result of declining freshwater input and consequent seawater density increase (Tsimplis and Baker, 2000). Looking to the future, the net effect of these processes is likely to be as much as 10% of global mean change to the 2080s (Gregory and Lowe, 2000).
Sea-level rise can cause several direct impacts, including inundation and displacement of wetlands and lowlands, coastal erosion, increased storm flooding and damage, increased salinity in estuaries and coastal aquifers, and rising coastal water tables and impeded drainage (Bijlsma et al., 1996). Potential indirect impacts are numerous; they include changes in the distribution of bottom sediments, changes in the functions of coastal ecosystems, and a wide range of socioeconomic impacts on human activities.
Other climate change factors also may be important. For example, rising air and sea temperatures may cause significant shifts in the timing and location of tourism (Perry, 1999) and recreational and commercial fisheries and decrease the incidence of sea ice during winter. These changes also may influence water quality through the occurrence of algal blooms, which would have adverse effects on tourism and human health (Kovats and Martens, 2000). Changes in the frequency and track of extratropical storms are less certain. It is worth noting that an analysis of the HadCM2 climate change simulations found a decrease in the number of northern hemisphere storms, but with a tendency for deeper low centers (Carnell and Senior, 1998). This would have important implications for coastal areas, including an additional increase in flood risk. Several studies suggest that storm surges in northwest Europe might change as a result of climate change (von Storch and Reichardt, 1997; Flather and Smith, 1998; Lowe and Gregory, 1998), but further investigation is required to produce definitive results. Storm occurrence has displayed significant interannual and interdecadal variability over the past 100 years (WASA, 1998); this could produce important and costly impacts without other changes (e.g., Peerbolte et al., 1991) and might interact adversely with sea-level rise.
The impacts of sea-level rise would vary from place to place and would depend on the magnitude of relative sea-level rise, coastal morphology/topography, and human modifications. The most threatened coastal environments within Europe are deltas, low-lying coastal plains, islands and barrier islands, beaches, coastal wetlands, and estuaries (Beniston et al., 1998). Tidal range is a key factor: In general, the smaller the tidal range, the greater the susceptibility to a given rise in sea level. The Mediterranean and Baltic coasts have a low tidal range (<1 m), which suggests that they will be more vulnerable to sea-level rise than the Atlantic Ocean and North Sea coasts (Nicholls and Mimura, 1998).
A regional/global model of flood and coastal wetland losses described by Nicholls et al. (1999) considers the interacting effects of sea-level rise, population growth, and improvements in protection standards. All other climate factors are assumed to be constant. This model allows the impacts of the SRES scenarios on Europe [excluding the former Soviet Union (FSU)] to be explored. Because increases in population and protection standards in Europe are minor, the major changes are caused by sea-level rise. In 1990, about 25 million people were estimated to live beneath the 1-in-1,000 year storm surge, with the largest exposure along the Atlantic/North Sea seaboard. However, these people generally are well protected from flooding now. The changes in flooding, shown in Table 13-3, indicate a significant increase in the incidence of coastal flooding by the 2080s, assuming no adaptation, particularly around the Mediterranean.
Europe (excluding the FSU) is estimated to have at least 2,860 km2 of saltmarshes and 6,690 km2 of other unvegetated intertidal habitat, mainly composed of sites recognized in the Ramsar treaty. Based on coastal morphological type and the presence or absence of coastal flood defenses, Table 13-4 shows wetland losses resulting from sea-level rise. Wetland losses are most significant around the Mediterranean and Baltic. Under the A2-high scenario, wetlands in these regions could be eliminated. Any surviving wetlands may be substantially altered. Such losses could have serious consequences for biodiversity in Europe, particularly for wintering shorebird and marine fish populations.
Available national results emphasize the large human and ecological values that could be affected by sea-level rise. Table 13-5 shows results of national assessments in The Netherlands (Baarse et al.,1994; Bijlsma et al., 1996), Poland (Zeidler, 1997), and Germany (Sterr and Simmering, 1996; Ebenhöh et al., 1997) for existing development and all costs adjusted to 1990 US$. In Table 13-5, adaptation assumes protection except in areas with low population density. People at risk are the numbers of people flooded by storm surge in an average year. Adaptation/protection costs for Poland include capital and annual running costs; % GNP assumes that costs are all incurred in 1 year. Subnational and local studies from East Anglia, UK (Turner et al., 1995); South Coast, UK (Ball et al., 1991); Rochefort sur Mer, France (Auger, 1994); Estonia (Kont et al., 1997); and Ukraine (Lenhart et al., 1996), as well as regional reviews (Tooley and Jelgersma, 1992; Nicholls and Hoozemans, 1996) also support this conclusion. Many of Europe’s largest cities—such as London, Hamburg, St. Petersburg, and Thessaloniki—are built on estuaries and lagoons (Frasetto, 1991). Such locations already are exposed to storm surges, and climate change is an important factor to consider for long-term planning and development.
Other values that may be affected include archaeological and cultural resources at the coast; these resources sometimes are being recognized only now (Fulford et al., 1997; Pye and Allen, 2000). In Venice, a 30-cm relative rise in sea level in the 20th century has greatly increased the frequency of flooding and damage to this unique medieval city; solutions to this problem are the subject of a continuing debate and need to consider climate change (Consorzio Venezia Nuova, 1997; Penning-Rowsell et al., 1998).
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