Marine-related physical natural hazards affecting coastal megacities of the Asia-Pacific region - awareness and mitigation

The fast-growing, coastal megacities of the Asia-Pacific region are expanding into areas that are vulnerable to marine-related physical natural hazards, or, because of physical environmental changes, will become increasingly vulnerable within the timescale of city planning. The hazards comprise those that are due to extreme events such as storm surge and tsunami which may be catastrophic in their impacts; and those that relate to continuing changes over the long-term, notably global sea-lever rise, sedimentary consolidation and coastal erosion. The latter may be exacerbated by human activities such as the increasing production of 'greenhouse' gases and over-abstraction of groundwater, and, while not threatening catastrophic loss of life or destruction of property, do have important economic and social implications for the future. There are two complementary approaches to hazard mitigation - constraining the hazard, and reducing vulnerability to the hazard. The contributions that science can make in the planning and implementation of sustainable adaptive measures are to improve the quantification of the incidence and severity of the various hazards, establishing realistic timescales of incidence, estimating return periods; and to establish the geographical limits of vulnerability to the hazards in a range of likely scenarios over timescales appropriate to the planning cycle. Contemporary, high risk, hazard scenarios for existing city developments demand an approach which focuses on effective warning networks and emergency planning; long-term, incremental hazards that are forecast to affect both developed and periurban areas can be addressed with a strategic planning approach, involving relocation and capital protective works. The selection of strategic measures demands the best possible predictive information on hazards and on vulnerability, including its full socio-economic evaluation so that the costs and benefits of the possible mitigation options can be realistically assessed. A predictive capacity, developed through modelling, requires the collection of reliable baseline and monitoring data relating to the hazards over a range of timescales in local, regional and global perspectives. (C) 1998 Natural Environment Research Council. Elsevier Science Ltd.