Of all the systems that are sensitive to climatic change, the cryosphere may be the most vulnerable; no adaptation measure can counter the disappearance of snow and ice in an environment that is likely to experience more frequent episodes of above-freezing temperatures than at present. In very restricted situations, the use of snowmaking equipment may help to extend the skiing season in particular areas, but this solution is expensive, and its environmental impact has not been fully evaluated.
In terms of water resource management, technological measures-including land-use criteria and erosion control, reservoirs and pipelines to increase the availability of freshwater supply, and improvements in the efficiency of water use-can be envisaged. Socioeconomic options should include direct measures to control water use and land use, as well as indirect measures such as incentives or taxes; institutional changes for improved resource management also may be needed. Specific examples of possible options include supplementing rain-fed agriculture with irrigation; water-conserving irrigation practices; enhanced coordination of surface and groundwater management; changes in cropping patterns; watershed management; structural and nonstructural flood-control management; and reallocation of water resources among water-use sectors and among nations.
Coastal zones are characterized by highly diverse ecosystems that are important as sources of food and habitats for many species. In many areas in Europe, population, economic activity, and arable land are concentrated in coastal zones, which has led to a decrease in their resilience and adaptability to variability and change. Some coastal areas-such as much of The Netherlands, the fens in eastern England, and the Po River plain (Italy)-already are beneath mean sea level; many more areas are vulnerable to flooding from storm surges. Fixed, rigid flood defenses and sea-level rise already are causing "coastal squeeze" (i.e., a decline in intertidal coastal habitats).
Sea-level rise and possible changes in the frequency and/or intensity of extreme events-such as temperature and precipitation extremes, cyclones, and storm surges-represent consequences of climate change that are of most concern to coastal zones. Except for sea-level rise itself, there currently is little understanding of the possible interaction of different aspects of climate change in the coastal zone. Other possible changes in climate could be costly. In The Netherlands, the costs of protection against an adverse 10% change in the direction and intensity of storms may be worse than the costs of a 60-cm rise in sea level (Peerbolte et al., 1991; IPCC 1996, WG II, Chapter 9).
Under the IS92a scenario, global sea level is projected to rise by about 5 mm/yr (with an uncertainty range of 2-9 mm/yr). This increase is two to five times the rate experienced over the past century. Regional and local sea-level rise will not necessarily be the same as the global average because of vertical land movements (glacial isostatic rebound, tectonic activity, subsidence) and possible changes in ocean water characteristics (oceanic circulation, wind and pressure patterns, ocean water density). Other climatic change in Europe is uncertain. An increase in precipitation intensity seems likely, increasing the flood risk in low-lying coastal areas.
Without adaptation, a rise in sea level would inundate and displace wetlands and lowlands, erode shorelines, exacerbate coastal storm flooding, increase the salinity of estuaries, threaten freshwater aquifers, and otherwise impact water quality. The impacts would vary from place to place and would depend on coastal type and relative topography. Areas most at risk would be tidal deltas, low-lying coastal plains, beaches, islands (including barrier islands), coastal wetlands, and estuaries. Tidal range also is a key factor: In general, the smaller the tidal range, the greater the response to a given rise in sea level. This pattern suggests that the Mediterranean and Baltic coasts, with their low tidal range, may be more vulnerable to sea-level rise than the open ocean coasts.
Examples of susceptible coasts include the Rhone, Po, and Ebro deltas (Jimenez and Sanchez-Arcilla, 1997; Sanchez-Arcilla and Jimenez, 1997). These areas already are subsiding because of natural and sometimes human factors, and they are sediment-starved as a result of changes in catchment management. For example, the Ebro delta has lost 97% of its sand supply since the 1950s. Reduction or loss of these areas would impact important agricultural and natural values. Many of Europe's largest cities-such as London, Hamburg, St. Petersburg, Thessaloniki, and Venice-are built on estuaries and lagoons (Frasetto, 1991). Such locations are exposed to storm surges, and climatic change is an important factor to consider for long-term development. In Venice, a 30-cm rise in relative sea level this century has greatly exacerbated flooding and damage to this unique medieval city; permanent solutions to this problem are still being investigated. Beaches tend to erode given sea-level rise, which destroys a valuable resource and exposes human activities landward of the beach to increased wave and flood action. Intense recreational use of beaches in many coastal areas, particularly around the Mediterranean, makes this erosion a particular problem; some response to such changes often is essential. In higher latitudes, gravel beaches are more common than sand beaches (Carter and Orford, 1993). Gravel beaches often provide an important coastal protection function, which sea-level rise may disrupt.
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