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In line with global trends, more than half of the region's population—1.7 billion people—presently resides in the coastal zone of Asia (Middleton, 1999). Given the relentless and cumulative process of global environmental change driven by, among other factors, demographic changes, urbanization and industrial development, trade and transport demands, and lifestyle changes, the coastal zones of Asia are under increasing anthropogenic pressures (Turner et al., 1996). The consequences of this process pose a significant threat to environmental and socioeconomic systems located in Asian coastal zones. All coastal areas are facing an increasing range of stresses and shocks, the scales of which now pose a threat to the resilience of human and environmental coastal systems and are likely to be exacerbated by climate change.
Climate impacts on coastal zones of Asia include accelerated sea-level rise and more frequent and severe storm events. Large populations in coastal areas of southeast and south Asia are vulnerable to pressure from unsustainable resource use and environmental degradation (e.g., Dow, 1999). These areas already are subject to numerous climate change-related stresses, including loss of coastal mangroves that act as major environmental determinants of coastal fisheries (Daily, 1997; Field et al., 1998; Primavera, 1998). Major delta areas of Asia are likely to be subjected to stresses associated with sea-level rise, changes in water regimes, saltwater intrusion, siltation, and land loss (see Chapter 6). Low-lying coastal cities will be at the forefront of impacts; these cities include Shanghai, Tianjin, Guangzhou, Jakarta, Tokyo, Manila, Bangkok, Karachi, Mumbai, and Dhaka—all of which have witnessed significant environmental stresses in recent years. Jakarta, Bangkok, and Tianjin, for example, have experienced changes in relative sea level of as much as 5 cm yr-1 during the 1980s and 1990s as a result of subsidence associated with groundwater withdrawal (ESD-CAS, 1994; Nicholls, 1995). In addition, increases in temperature can lead to increased eutrophication in wetlands and freshwater supplies.
Tropical Asia experiences the impact of present-day climate variability associated with ENSO, therefore is more prone to changes in ENSO-related impacts with global climate change. The ENSO phenomenon is a major cause of year-to-year variability in the number of cyclones in the Asia Pacific region (Li, 1987; Nishimori and Yoshino, 1990; Lander, 1994). The numbers are higher during La Niña events, particularly late in the season over southeast Asia (Kelly and Adger, 2000). The 1982-1983 El Niño caused a decline in rainfall and associated impacts over large areas, including parts of Indonesia (Salafsky, 1994, 1998; Glantz, 1996). El Niño events are known to have significant impacts on coastal areas and water resources in southeast Asia through decreased precipitation in El Niño years and increased frequency of typhoons in subsequent La Niña years (Kelly and Adger, 2000).
Sea levels of interior seas in arid and semi-arid Asia have dramatically changed, driven either by climatic or anthropogenic factors. The level of the Caspian Sea lowered by about 4 m from 1930 to 1977; since 1978 it has begun rising (Mikhailov, 1998). The coastline also propagated landward by 20-40 km; 2 Mha of farming land and more than 100 oil wells have been inundated. Many cities in the coastal zone, such as Makhachkala and Kaspisk, are seriously damaged (Svitoch, 1997). The Volga delta propagated 17 km during the period of lowering sea level but has retreated 12-15 km during the period of the rise in sea level (Kasimov, 1997; Tian and Liu, 1999). Caspian Sea level fluctuations are attributed mainly to the Volga water discharge controlled by climate anomalies in its catchment area (Malinin, 1994). The Aral Sea area also reduced, from 60,000 to 28,500 km2, in the period 1960-1989; the exposed seabed (particularly deltas) now have frequent dust and salt storms, and there are shortages of freshwater (Ellis, 1990; Tian and Liu, 1999).
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