Comprehensive Risk Assessment for Natural Hazards - Planat

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Comprehensive risk assessment for natural hazards local people in the assessments should include: seeking information and advice from them; training those with the technical background to undertake the assessments themselves; and advising those in positions of authority on the interpretation and use of the results. It is of limited value for experts to undertake all the work and provide the local community with the finished product. Experience shows that local communities are far less likely to believe and use assessments provided by others and the development of local expertise encourages further assessments to be made without the need for external support. As discussed briefly in this section, it is evident that comprehensive risk assessment would benefit from further refinement of approaches and methodologies. Research and development in various areas are encouraged, particularly in the assessment of vulnerability, risk assessment and the compatibility of approaches for assessing the probability of occurrence of specific hazards. It is felt that that society would benefit from the application of the various assessment techniques documented herein that constitute a comprehensive assessment. It is hoped that such applications could be made in a number of countries. These applications would involve, among a number of items: • agreeing on standard terminology, notation and symbols, both in texts and on maps; • establishing detailed databases of natural systems and of primary land uses; • presenting descriptive information in an agreed format; • using compatible map scales, preferably identical base maps; • establishing the local level of acceptable risk; • establishing comparable probabilities of occurrence for various types of hazards; and • establishing mitigation measures. As mentioned, the techniques and approaches should be applied, possibly first in pilot projects in one or more developing countries. Stress should be placed on a coordinated multidisciplinary approach, to assess the risk of combined hazards. The advancement of mitigation efforts at the local level will result through, in part, the application of technologies, such as those documented herein. 1.4 REFERENCES Bondi, H., 1985: Risk in Perspective, in Risk: Man Made Hazards to Man, Cooper, M.G., editor, London, Oxford Science Publications. Gilard, O., 1996: Risk Cartography for Objective Negotiations, Third IHP/IAHS George Kovacs Colloquium, UNESCO, Paris, France, 19-21 September 1996. Karlsson, P-O. and Y.Y. Haimes, 1989: Risk assessment of extreme events: application, Journal of Water Resources Planning and Management, ASCE, 115(3), pp. 299-320. Schwing, R.C., 1991: Conflicts in health and safety matters: between a rock and a hard place, in Risk-Based Decision Making in Water Resources V, Haimes, Y.Y., Moser, D.A. and Stakhiv, E.Z., editors, New York, American Society of Civil Engineers, pp. 135-147. Thompson, K.D., J.R. Stedinger and D.C. Heath, 1997: Evaluation and presentation of dam failure and flood risks, Journal of Water Resources Planning and Management, American Society of Civil Engineers, 123 (4), pp. 216-227. United Nations Department of Humanitarian Affairs (UNDHA), 1992: Glossary: Internationally Agreed Glossary of Basic Terms Related to Disaster Management, Geneva, Switzerland, 93 pp. United Nations General Assembly, 1989: International Decade for Natural Disaster Reduction (IDNDR), Resolution 44/236, Adopted at the forty-fourth session, 22 December. Viscusi, W.K., 1993: The value of risks to life and health, Journal of Economic Literature, 31, pp. 1912-1946. 5
Chapter 2 METEOROLOGICAL HAZARDS 2.1 INTRODUCTION Despite tremendous progress in science and technology, weather is still the custodian of all spheres of life on earth. Thus, too much rain causes flooding, destroying cities, washing away crops, drowning livestock, and giving rise to waterborne diseases. But too little rain is equally, if not more, disastrous. Tornadoes, hail and heavy snowfalls are substantially damaging to life and property. But probably most alarming of all weather disturbances are the low pressure systems that deepen and develop into typhoons, hurricanes or cyclones and play decisive roles in almost all the regions of the globe. These phenomena considerably affect the socioeconomic conditions of all regions of the globe. The objective of this chapter is to provide a global overview of these hazards; their formation, occurrence and life-cycle; and their potential for devastation. It must, however, be pointed out that these phenomena in themselves are vast topics, and it is rather difficult to embrace them all in their entirety within the pages of this chapter. Thus, because of the severity, violence and, most important of all, their almost unpredictable nature, greater stress is laid upon tropical storms and their associated secondary risks such as storm surge, rain loads, etc. 2.2 DESCRIPTION OF THE EVENT 2.2.1 Tropical storm In the tropics, depending on their areas of occurrence, tropical storms are known as either typhoons, hurricanes, depressions or tropical storms. In some areas they are given names, whereas in others they are classified according to their chronological order of occurrence. For example, tropical storm number 9015 means the 15th storm in the year 1990. The naming of a tropical storm is done by the warning centre which is responsible for forecasts and warnings in the area. Each of the two hemispheres has its own distinct storm season. This is the period of the year with a relatively high incidence of tropical storms and is the summer of the hemisphere. In some regions, adjectives (weak, moderate, strong, etc.) are utilized to describe the strength of tropical storm systems. In other regions, tropical storms are classified in ascending order of their strength as tropical disturbance, depression (moderate, severe) or cyclone (intense, very intense). For simplicity, and to avoid confusion, all through this chapter only the word tropical storm will be used for all tropical cyclones, hurricanes or typhoons. Furthermore, the tropical storm cases dealt with in this chapter are assumed to have average wind speed in excess of 63 km/h near the centre. During the period when an area is affected by tropical storms, messages known as storm warnings and storm bulletins are issued to the public. A storm warning is intended to warn the population of the impact of destructive winds, whereas a storm bulletin is a special weather message providing information on the progress of the storm still some distance away and with a significant probability of giving rise to adverse weather arriving at a community in a given time interval. These bulletins also mention the occurring and expected sustained wind, which is the average surface wind speed over a ten-minute period; gusts, which are the instantaneous peak value of surface wind speed; and duration of these. Extratropical storms, as their names suggest, originate in subtropical and polar regions and form mostly on fronts, which are lines separating cold from warm air. Depending on storm strength, warning systems, which are not as systematically managed as in the case of tropical storms, are used to inform the public of the impending danger of strong wind and heavy precipitation. Warnings for storm surge, which is defined as the difference between the areal sea level under the influence of a storm and the normal astronomical tide level, are also broadcast in areas where such surges are likely to occur. Storm procedures comprise a set of clear step-by-step rules and regulations to be followed before, during and after the visit of a storm in an area. These procedures may vary from department to department depending on their exigencies. Tropical storms are non-frontal systems and areas of low atmospheric pressure. They are also known as “intense vertical storms” and develop over tropical oceans in regions with certain specific characteristics. Generally, the horizontal scale with strong convection is typically about 300 km in radius. However, with most tropical storms, consequent wind (say 63 km/h) and rain start to be felt 400 km or more from the centre, especially on the poleward side of the system. Tangential wind speeds in these storms may range typically from 100 to 200 km/h (Holton, 1973).Also characteristic is the rapid decrease in surface pressure towards the centre. Vertically, a well-developed tropical storm can be traced up to heights of about 15 km although the cyclonic flow is observed to decrease rapidly with height from its maximum values in the lower troposphere. Rising warm air is also typical of tropical storms. Thus, heat energy is converted to potential energy, and then to kinetic energy. Several UN-sponsored symposia have been organized to increase understanding of various scientific aspects of the phenomena and to ensure a more adequate protection against the destructive capabilities of tropical storms on the basis of acquired knowledge. At the same time, attempts have been made to harmonize the designation and classification of tropical storms on the basis of cloud patterns, as depicted by satellite imagery, and other measurable and determinable parameters. 2.2.2 Necessary conditions for tropical storm genesis It is generally agreed (Riehl, 1954; Gray, 1977) that the conditions necessary for the formation of tropical storms are:
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Chapter 6 HAZARD ASSESSMENT AND LAN
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CHAPTER 8 STRATEGIES FOR RISK ASSES
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