X = strong; x= weak; - = negligible or not established.

X = strong; x= weak; - = negligible or not established.

this will compound the impacts of other climate changes (see Chapter 10). Coastal ecosystems are particularly at risk from climate change (CBD, 2003; Section 6.4.1), with serious implications for the services that they provide to human society (see Section 6.2.2; Box 6.4 and Chapter 4, Section 4.4.9).

Since the TAR, some important observations on the impacts and consequences of climate change on human society at coasts have emerged. First, significant regional differences in climate change and local variability of the coast, including human development patterns, result in variable impacts and adjustments along the coast, with implications for adaptation responses (Section 6.6). Second, human vulnerability to sea-level rise and climate change is strongly influenced by the characteristics of socio-economic development (Section 6.6.3). There are large differences in coastal impacts when comparing the different SRES worlds which cannot be attributed solely to the magnitude of climate change (Nicholls and Lowe, 2006; Nicholls and Tol, 2006). Third, although the future magnitude of sea-level rise will be reduced by mitigation, the long timescales of ocean response (Box 6.6) mean that it is unclear what coastal impacts are avoided and what impacts are simply delayed by the stabilisation of greenhouse gas concentration in the atmosphere (Nicholls and Lowe, 2006). Fourth, vulnerability to the impacts of climate change, including the higher socio-economic burden imposed by present climate-related hazards and disasters, is very likely to be greater on coastal communities of developing countries than in developed countries due to inequalities in adaptive capacity (Defra, 2004; Section 6.5). For example, one quarter of Africa's population is located in resource-rich coastal zones and a high proportion of GDP is exposed to climate-influenced coastal risks (Nyong and Niang-Diop, 2006; Chapter 9). In Guyana, 90% of its population and important economic activities are located within the coastal zone and are threatened by sea-level rise and climate change (Khan, 2001). Low-lying densely populated areas in India, China and Bangladesh (see Chapter 10) and other deltaic areas are highly exposed, as are the economies of small islands (see Chapter 16). Freshwater resources

The direct influences of sea-level rise on freshwater resources come principally from seawater intrusion into surface waters and coastal aquifers, further encroachment of saltwater into estuaries and coastal river systems, more extensive coastal inundation and higher levels of sea flooding, increases in the landward reach of sea waves and storm surges, and new or accelerated coastal erosion (Hay and Mimura, 2005). Although the coast contains a substantial proportion of the world's population, it has a much smaller proportion of the global renewable water supply, and the coastal population is growing faster than elsewhere, exacerbating this imbalance (see Section 6.2.2 and Chapter 3, Section 3.2).

Many coastal aquifers, especially shallow ones, experience saltwater intrusion caused by natural and human-induced factors, and this is exacerbated by sea-level rise (Essink, 2001). The scale of saltwater intrusion is dependent on aquifer dimensions, geological factors, groundwater withdrawals, surface water recharge, submarine groundwater discharges and precipitation. Therefore, coastal areas experiencing increases in precipitation and run-off due to climate change (Section 6.3.2), including floods, may benefit from groundwater recharge, especially on some arid coasts (Khiyami et al., 2005). Salinisation of surface waters in estuaries is also promoted by a rising sea level, e.g., Bay of Bengal (Allison et al., 2003).

Globally, freshwater supply problems due to climate change are most likely in developing countries with a high proportion of coastal lowland, arid and semi-arid coasts, coastal megacities particularly in the Asia-Pacific region, and small island states, reflecting both natural and socio-economic factors that enhance the levels of risks (Alcamo and Henrichs, 2002; Ragab and Prudhomme, 2002). Identifying future coastal areas with stressed freshwater resources is difficult, particularly where there are strong seasonal demands, poor or no metering, and theft of water (Hall, 2003). Overall efficiency of water use is an important consideration, particularly where agriculture is a large consumer, e.g., the Nile delta (see Chapter 9, Box 9.2) and Asian megadeltas.

Based on the SRES emissions scenarios, it is estimated that the increase in water stress would have a significant impact by the 2050s, when the different SRES population scenarios have a clear effect (Arnell, 2004). But, regardless of the scenarios applied, critical regions with a higher sensitivity to water stresses, arising from either increases in water withdrawal or decreases in water available, have been identified in coastal regions that include parts of the western coasts of Latin America and the Algerian coast (Alcamo and Henrichs, 2002).

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