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Lecture

# 7._Risk_assesst_and_mgmt-2.pdf

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School
Department
Course
Professor
Uma Acharya
Semester
Summer

Description
ADMS3701: Meeting-Groups-3,4,5 Disaster Risk Management WEEK-4.1 Lecture Plan Last week • Risk Assessment and Management: – Risk assessment: quantitative and qualitative • Extreme event analysis – Risk categories: voluntary and involuntary • Risk perceptions and communication – Multiplication and addition theories – Event tree technique – Magnitude and frequency relationships – Stages Smith et.al., ‘Hazards’ book, Chapter 4- ‘risk assessment and management’ The book is available as ebook online through the Scott Library at the following link : http://www.library.yorku.ca/find/Record/2464122 1 EXTREME EVENT ANALYSIS Extreme event analysis concerned with the distribution of annual maximum or minimum values at a given site- to forecast recurrence and probability of annual frequency Example: annual maximum wind gusts recorded at Tiree in western Scotland Continued… over a 59-year period from 1927 to 1985. • These events can be given a rank, m, starting with m = 1 for the highest Disaster Risk recorded wind gust, m = 2 for the next highest and so on in descending order. • The return period or recurrence interval Tr (in years) can then be computed Assessment and from Tr (years) = (n +1)/ m Management • where m = event ranking and n = number of events in the period of record. The percentage probability for each event may then be Pbtained from : (per cent) = 100/Tr • The annual frequency (AF) can be given by: 1/ Tr (years) = AF EXTREME EVENT ANALYSIS EXTREME EVENT ANALYSIS Example: 39 years of data available • In all probability based approaches reliability of Rank intensity flood rate 4 the results depend on the qualities of database Annual frequency AF=1/ Tr (years)? • Predictions are based on past records and • Tr (years) = (n +1)/ m assumptions that there will be no change in the • where m = event ranking and n = number of events in the environment in the future, known as stationarity period of record. The percentage probability for each assumption-which ignores environmental change event may then be obtained from and is based on normal distribution of data within • 39+1 =10 return period the population. 4 • changes occur naturally and are also human 100/10=10 percentage probability of return/occurrence induced each year • AF= 1/10= 0.10 2 Risk perception and communication Approaches to study Risk Perceptions: Risk is perceived in two ways: Two common approaches: • Objective- (statistical) view of risk • Subjective- (perceived) view of risk-perception • revealed preferences: observes how people behave- takes this as a reflection of public perception by Risk perception – includes emotions, personal assuming that, through trial and error, society has preferences arrived at an ‘acceptable’ balance between the risks and • Purely qualitative, cannot be replicated in its benefits associated with any activity. entirety • Risk means different things to different people • expressed preferences : uses questionnaire surveys- • All individual perceptions of risk are regarded as samples of people to express verbally what their equally valid and, for any given threat, each preferences are individual chooses – within the available limits – their own response. Risk perceptions: three basic types • Determinate perception/determinism- (gambler’s fallacy) Risk perceptions: types – exists when lay people find difficult to accept the random element of hazardous events Probabilistic perception
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