IDNDR-ESCAP Regional Meeting for Asia: Risk Reduction & Society in the 21st Century
Bangkok, 23-26 February 1999
Water Hazards, Resources and Management for Disaster Prevention:
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Disaster risk management involves the assessment of hazard and vulnerability.
Hazard assessment is concerned with defining the properties of the hazard and its direct effect. The first step in hazard assessment is data collection and recording. Tropical cyclones pose three threats, namely, wind, flood and storm surge. The intensity of a tropical cyclone is measured by its wind characteristics which are described by velocity and direction. Evaluation of the hazard associated with cyclones therefore involves the measurement of wind direction, velocity and frequency at a number of meteorological stations.
The assessment of the flood hazard involves the identification of:
When combined, these elements define the nature and extent of the flood hazard at a particular locality. Generally, this information is presented in map form showing the areas which are likely to be inundated to a given depth with a specified frequency.
For hazard evaluation of storm surge, it is necessary to determine the frequency of intense winds, the topography of the continental shelf and adjacent coastline and the normal tidal behaviour.
In evaluating the relationship of hazards to the elements at risk, it is important that the analysis is applied to the entire disaster episode, encompassing onset, response, aftermath and recovery phases. Different sets of ‘elements at risk’ will emerge in the different phases of the disaster episode. For example, the threat to life and limb of the disaster prone residents is an issue during the response phase, while the rapid return of the water supply, sewerage and communication systems to serviceability is an issue during the recovery phase.
On the other hand vulnerability is a measure of the level of exposure of people and property to the various water-related hazards. Vulnerability can be measured as:
These three items, taken collectively and combined with damage information, measure the probable damage for a given frequency of hazard. When the potential damage for a given disaster has been assessed, the disaster risk can be determined by the product of the damage and the probability of occurrence of the disaster. It is usually only possible to express physical vulnerability in monetary terms.
Vulnerability is a measure of the degree of susceptibility and resilience of a disaster prone community. Vulnerability determines how well a community can cope with a disaster. This in turn depends upon the magnitude of the disaster, the disaster awareness of the community and the topographic, infrastructure, social and economic factors which determine the social and economic disruption caused by the hazard.
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By evaluating the risk of various hazards to which the country is liable or potentially liable, it becomes practicable to formulate strategies to mitigate the impact of hazards in a cost-effective way. If a community is especially vulnerable to a particular type of disaster severe risk treatment measures may be required to reduce the disaster risk to acceptable levels.
More recently, the definition of risk management has been expanded to include the notion of uncertainty. "Risk" is defined as the possibility that an expected outcome is not achieved or replaced by another, or that an unforeseen event occurs. This is a broad view of risk that includes both uncertainty due to future events and the consequences of limited knowledge, information and experience. "Uncertainty" describes the lack of sureness about something and can be represented by a probability distribution of error.
Disaster mitigation projects, as currently undertaken, are formulated to provide economical protection to disaster prone areas. Projects are determined by analyzing disaster potential, together with damage performance and cost, for a range of project sizes and configurations. The disaster mitigation plan selected is based on maximizing net economic benefits consistent with acceptable risk and functional performance. This approach treats the input variables as deterministic functions.
The trend is now towards the use of a combined risk model which incorporates "uncertainty" into the input variables as a probability density function representing possible statistical error in each of the input variable relationships. This risk management approach acknowledges that there is not a specific, unequivocal performance level.
Initially, the evaluation of risk, or the evaluation of disaster potential, is based on the analysis of available meteorological and hydrological records of the individual country, augmented by data available from other countries in the region, depending on the nature of the disaster.
Meteorological data for hazard assessment need to be based on a comprehensive, nation-wide system of meteorological recording stations. It is also highly desirable that this system is closely associated with, and compatible with, the national meteorological recording systems operated by neighbouring countries. The main categories of meteorological data needed for effective water-based natural disaster identification are:
Hydrological data for hazard assessment should also be based on a comprehensive, nation-wide system of stream gauging stations. There are three major components of hydrological data required for hazard assessment, namely, flood discharges, water levels and flow velocities. Long-term streamflow data are also required to predict and quantify drought behaviour. Where rivers cross international boundaries, the free exchange of data is vital for flood forecasting activities.
Over the past decade, remote sensing techniques have become an essential feature of data collection systems for monitoring watershed conditions. These techniques are invaluable for the rapid collection of data and for the study of extensive areas, particularly in developing countries for which conventional resource mapping sources are limited. Under favourable conditions, they are well suited for reconnaissance studies of water-related disasters affecting large areas, such as flooding.
Normal aerial photography has proved to be a useful technique for watershed monitoring, because of the high degree of resolution obtainable and the ability of this technique to show the spatial distribution of ground characteristics.
By comparison with conventional aerial photography, satellite imagery has the major advantage of low cost, enabling a much larger area to be covered by a smaller number of prints. However, the ground resolution capability of this form of imagery is much lower than that achievable with aerial photography, which generally limits the scope of its application to reconnaissance level mapping.
Over the past twenty years, the enormously increased amount of resource evaluation and assessment data available from the various types of remote sensing systems, much of it available directly in computer accessible format, and increasingly widespread availability of low-cost computer equipment, has greatly encouraged the development of techniques for the archiving, analysis, mapping and presentation of such data, using GIS methodology. These techniques are supported by a wide-range of commercial software packages and systems which allow the ready manipulation of vast amounts of data. Available computer models have been developed to predict the flood behaviour of river flow, such as rates of rise and fall, duration, frequency and magnitude of floods and periods of low flow.
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In the light of the many major disasters experienced throughout the Region during the past decade, it would be desirable to review the disaster management practices of the member countries. The experiences gained should be used as a basis to assist further evolution of disaster management practices, especially in those areas where implementation practices could be improved.
Wholesale changes do not appear warranted but adjustments to the existing approach would achieve:
To achieve these objectives, there appears to be a case for the adoption of a system which could be effectively implemented as part of the member’s disaster strategies.
After examining the available information on the status of disaster management in the ESCAP region, it is apparent that many of the member countries are yet to adopt an integrated approach for disaster management. The preferred disaster management system should integrate the following elements:
The objectives of the overall management system should ensure that:
An integrated approach is required to bring together these diverse issues, which are usually fragmented over a number of different authorities. This can be achieved through greater cooperation amongst the agencies, authorities and individuals involved in all aspects of disaster prevention and preparedness. The extent to which the integrated approach can be achieved relies on a number of factors, including the management of natural resources and the strength of existing legislation. As a general principle however, the overall coordination of disaster management plans should be vested in a single organization, preferably operating at the national level, which assumes responsibility for legal, administrative and financial matters relating to the management of natural disasters.
The ultimate goals of integrated disaster management should be to limit the hazards and damages to socially acceptable levels, to promote environmental enhancement and to provide disaster warning, response, evacuation and recovery from the onset to the aftermath of the disaster.
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The adoption of such a system could however pose a problem for some countries, which may lack the specialist technical skills needed to develop a comprehensive management plan and the capacity to implement the resulting prevention and preparedness measures. These problems could be addressed by the provision of specialist professional support and training for their agencies and institutions and financial subsidies from national governments and donor countries.
The disaster management process requires an ongoing commitment to the education and training of disaster managers by the various tiers of government and professional bodies. The exchange of information regarding difficulties, problems and solutions and the results of research is essential for improved disaster management. This can be fostered by the free flow of information at the local and international levels through formal agreement, workshops and conferences.
There is a number of significant advantages to be gained by adopting a national and international approach to water-related disaster management. This approach would lead to a better and more efficient use of the resources of each nation and the region. Disaster management principles have developed to a different degree and in different ways in the various ESCAP countries. Considerable cost savings and efficiencies could be achieved through the sharing of information and experiences in the coordination of disaster management research activities among the various countries. This form of cooperation would promote a consistent approach to disaster management policies and techniques, leading to better disaster management practices, and would help to reduce each country’s exposure to the risk of future disasters. Moreover, wider cooperation amongst neighbouring countries would facilitate the development of a regional data base of disaster related information throughout the region. This information should promote a better and more efficient allocation of resources to disaster management both within individual countries and across the region.