A global review of disaster reduction initiatives - Welcome to the ...

2Living with Risk: A global review of disaster reduction initiativesHazard assessmentThe objective of a hazard assessment is to identifythe probability of occurrence of a specifiedhazard, in a specified future time period, aswell as its intensity and area of impact. Forexample, the assessment of flood hazard isextremely important in the design and settingof engineering facilities and in zoning for landuse planning. Construction of buildings andresidences is often restricted in high flood hazardareas. Flood assessment should be developedfor the design and setting of sewagetreatment as well as land and buildings havingindustrial materials of a toxic or dangerousnature, due to the potential spread of contaminants.Certain hazards have well-established techniquesavailable for their assessment. This isthe case for floods, earthquakes and volcanichazards. Many of the analytical techniquesuseful for hazard assessment can be appliedusing medium powered computers and widelyavailable software packages.On seismic hazards, the dynamic ground shakingand ground movement are the two mostimportant effects considered in the analysis.Dynamic ground shaking is a critical considerationfor buildings and construction. Theobjective of a statistical earthquake hazardassessment is to assess the probability that aparticular level of ground motion at a site isreached or exceeded during a specified timeinterval. An alternative approach is to considerWMO and the IDNDR Scientific and Technical Committeepromoted a project to further develop the concept of comprehensive,multi-hazard or joint assessment of natural hazards.It was recognised that society is usually at risk from severaldifferent hazards, many of which are not water-related or naturalin origin. More importantly, it was also recognised thatjoint assessment of risk from these various hazards is in itsinfancy. Recognising these points, the project focused on themost destructive and most widespread natural disasters, namelythose of meteorological, hydrological, seismic, and volcanicorigin. An example of the development and application ofsuch approach in land-use planning was provided by Switzerlandwhere the composite exposure to risks from floods, landslidesand avalanches were considered. The project noted thatan increased understanding of the hazard assessment methodologiesof each discipline is required, as these methodologiesvaried from discipline to discipline.68the evaluation of the ground motion producedby the maximum conceivable earthquake in themost unfavourable distance to a specific site.Earthquake hazard assessment in areas of lowseismic activity is much more subject to largeerrors than in areas with high earthquake activity.This is especially the case if the time span ofthe available data is considerably smaller thanthe mean return interval of large events, forwhich the hazard has to be calculated.In most cases, one is able to characterise theoverall activity of a volcano and its potentialdanger from field observations by mapping thevarious historical and prehistoric volcanicdeposits. These deposits can, in turn, be interpretedin terms of eruptive phenomena, usuallyby analogy with visually observed eruptions.Other hazards have less well-defined assessmentmethodologies. In the future, efforts must continue toincrease our understanding and develop methodologiesfor the assessment of hazards such as heatwaves and dust storms; in particular, with regardto the factors which influence their development,movement and decay.Multi-hazard assessments are difficult toachieve due in part to the different approachestaken by the various disciplines in assessing thespecific potential hazards. But multi-hazardassessments are essential, for example, in thecase of a tropical storm event. The event cannotbe looked at in isolation and should considerthe different components that actuallyrepresent the risks occurring either separatelyor all together. These components are flood,landslide, storm surge, tornado and wind. Varioushazards will be measured according to differentscales, which make comparisons difficult.An earthquake will be quantified based onthe amount of energy released (Richter scale)or the amount of damage potentially caused(Modified Mercalli scale), while a heat wave ismeasured using maximum temperatures and awind storm using wind velocity.Even without sophisticated assessment tools, itis possible for local communities to collect hazardinformation. Such steps are suggested inUNEP’s Technical Report N°12, HazardIdentification and Evaluation in a Local Community,consisting of basic checklists to identify,and basic approaches to map major hazards ina locality. Various tables invite more detailed