Risk is defined as the probability of meeting danger or suffering harm or loss. In relation to disaster, risk has been more specifically described as the probability that a disaster will occur, using relative terms such as high risk, average risk, and low-risk to indicate the degree of probability. Risk assessment includes an evaluation of all the elements that are relevant to an understanding of existing hazards and their effect on a specific environment. Knowledge of hazards is provided by the various physical sciences such as meteorology, hydrology, geomorphology, seismology, and volcanology. The understanding of vulnerability includes physical, social, and economic aspects. To turn risk assessment into a useful planning tool, accurate information must be gathered from numerous and diverse sources, ranging from remote sensing of crop yields to the monitoring of volcanic activity, to the historical records of floods or earthquakes, and social surveys of livelihoods, living patterns, and a community’s perception of risk. From these data, a fairly complete picture may be assembled of the prevailing risk expressed in terms of probabilities. There are several steps in risk assessment based on the related processes of hazard mapping and vulnerability analysis. They establish the nature, location, and scale of risks to society and its assets. This information can assist decision makers in deciding what can and should be protected and up to what level of safety, measured against the potentially disastrous effects of not initiating risk-reduction measures. Hazard Assessment Disasters result from vulnerable conditions being exposed to a potential hazard. Therefore, the first step in taking any mitigation measures is to assess the hazard. Hazard assessment aims to come to grips with: the nature, severity, and frequency of the hazard; the area likely to be affected; and The time and duration of impact. Hazard assessment concerns the properties of the hazard itself (i.e., cyclone, flood, drought, earthquake, volcanic eruption, etc.) and its direct effect, not its effect on the socioeconomic environment which is covered by vulnerability analysis. Hazard assessment begins with data collection; existing assessments and hazard maps; scientific data (meteorological, hydrological, seismological, volcano logical, etc.); other maps (topographical, geological, etc.); local lore and historical records; and socioeconomic or agricultural surveys. The data are then analysed. One effective way of presenting hazard assessment is through hazard mapping. Hazard maps can be of macro or micro scale; for cyclones (cyclone track maps, wind velocity zoning maps, and cyclone/storm surge hazard maps); for floods (inundation maps); for earthquake and tsunami (epicentre maps, seismic zoning maps, seismic zone source maps, tsunami hazard maps); and for landslides (landslide hazard maps). Next, data and maps are analysed to arrive at the hazard assessment. The level of sophistication of hazard assessment will depend on the perception of risk and available resources. Formats for expressing the intensity (power or impact) of a particular hazard are well established. Tropical cyclones can be measured in terms of wind speeds; floods in terms of return periods, duration, and inundation levels relative to normal river or
sea levels; earthquakes in terms of intensity indicating their effects on man-made structures or in terms of magnitude on the Richter scale. Finally, an attempt should be made to express the probability of the event occurring over time. Probabilities are assessed on the basis of scientific data and historical records. Sophisticated new tools are available to assist in hazard mapping and assessment. For instance, aerial photography and satellite imagery can provide information about the landscape, flooding, fissures, fault lines, etc. Microcomputers have a growing potential for applications in developing countries as they become more...
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