The impacts of climate change on coastal areas in Tropical Asia could be severe and in some areas catastrophic. Nicholls et al. (1995) estimate that (assuming no adaptation and no change in existing population) a 1-m rise in sea level could displace nearly 15 million, 7 million, and at least 2 million people from their homes in Bangladesh, India, and Indonesia, respectively; millions more could be threatened in Viet Nam, Myanmar, Thailand, and the Philippines. (Potential impacts on special tropical coastal ecosystems, including coral reefs and mangroves, are discussed in Section 11.3.2.)
Sea-level rise and heavy rainfall events are projected with some confidence to increase with climate change; these increases, superimposed on existing coastal problems, would have major impacts, regardless of whether there is any change in the frequency or intensity of tropical storms.
Projected impacts include:
Nicholls et al. (1995) consider the first of these impacts to be the most serious coastal issue in the region. They estimate that a 1-m rise in sea level could lead to land loss in Bangladesh, India, Indonesia, and Malaysia of nearly 30,000; 6,000; 34,000; and 7,000 km2, respectively. In Viet Nam, 5,000 km2 of land could be inundated in the Red River delta, and 15,000-20,000 km2 of land may be threatened in the Mekong delta.
Several studies have been undertaken on the vulnerability of Bangladesh to climate change, particularly to sea-level rise. A comprehensive summary appears in Warrick and Ahmad (1996). Recent geological studies suggest that the magnitude of tectonic subsidence in the Ganges-Brahmaputra delta of Bangladesh is greater than has been taken into account in some earlier projections; this subsidence is expected to result in higher estimates of relative sea-level rise. Around the city of Dhaka, average subsidence is about 0.62 mm/yr; elsewhere, it can exceed 20 mm/yr (Alam, 1996).
The Ganges-Brahmaputra delta is one of the world's most densely populated areas, and the combined effects of subsidence and sea-level rise could cause serious drainage and sedimentation problems, in addition to coastal erosion and land loss. With higher sea level, more areas would be affected by cyclonic surges; inland freshwater lakes, ponds, and aquifers could be affected by saline and brackish-water intrusion. The present limit of tidal influence is expected to move further upstream, and increases in soil salinity, as well as surface-water and groundwater salinity, may cause serious water supply problems for drinking and irrigation over large areas (Alam, 1996). Reduced dry-season freshwater supply from upstream sources may further exacerbate salinity conditions in the coastal area of Bangladesh. These impacts clearly would have immense socioeconomic costs.
The other large deltaic areas in Tropical Asia-such as the Irrawaddy in Myanmar and the Mekong and Red in Viet Nam-as well as smaller deltaic regions and low-lying coastal plains in India, Thailand, Cambodia, Malaysia, Indonesia, and the Philippines will be affected in similar ways. Specific examples of vulnerability assessments and impact analyses for several south and southeast Asian countries are given in McLean and Mimura (1993), Chou (1994), Nicholls and Leatherman (1995), Erda et al. (1996), and Milliman and Haq (1996).
The magnitude of physical and socioeconomic impacts of sea-level rise alone on a small segment of the Malaysian coast in West Johor, which is occupied by 150,000 people, has been detailed by Teh and Voon (1992). In this example, a projected coastal embankment failure resulting from sea-level rise would result in a substantial reduction in the area under agriculture and extensive damage to houses, schools, and other social amenities. In addition, millions of dollars of revenue loss from the destruction of the three main crops (coconuts, oil palm, and rubber) ultimately could involve a population shift inland. This example is duplicated many times in the region, with the implication that greenhouse-induced sea-level rise may require a reassessment of existing and future coastal developments-as has been done in Malaysia (Midun and Lee, 1995).
In the previous example, the area was essentially rural and agricultural. The potential impact of sea-level rise on recreational and tourist sectors-for example, on the east coast of peninsular Malaysia (Wong, 1992) and at Phuket, Thailand (Wong, 1995)-and on infrastructure, harbors, and airports also would be severe. Indeed, Nicholls (1995) shows that present and future megacities of the region-including Jakarta, Bangkok, and Manila-are especially vulnerable. For Bangkok, the steady rise in sea level poses a threat for the investment, operation, and safety levels of the flood-control system, which could have an estimated annual pumping cost of up to US$20 million (Sabhasri and Suwarnarat, 1996).
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