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Title: Mitigation of the Impact of Tornadoes in the Canadian Prairies
Author: Walawe Durage, Samanthi
Advisor: Wirasinghe, S.C.
Ruwanpura, Janaka
Keywords: Engineering--Civil
Issue Date: 1-May-2014
Abstract: Tornadoes are a destructive form of the extreme weather associated with thunderstorms. Canada gets more tornadoes than any other country with the exception of the United States. This thesis is the first study centered on the mitigation of the impact of tornadoes in the Canadian Prairies. Initially, a regression based analysis of the Prairie tornado database is conducted to obtain the trend for the number of tornadoes reported in each year. Given that the population is an influencing factor; both population and time are considered as important parameters in the model development. Based on this analysis, a wave form for the time trend with a period of around 65 years is recognized. The detection, warning and communication stages at the pre-touchdown phase of a tornado are analyzed using network modelling and simulation methods. The simulation results of the network developed for the City of Calgary illustrating the role of collaborating partners provide a probabilistic representation of the overall time consumption from tornado detection point to the warning completion point. Furthermore, a qualitative comparison of the Canadian tornado detection, warning and communication system with the US system supports the recognition of key areas that need to be improved. The evacuation response behaviour of households and drivers during a tornado is analyzed through a stated preference survey. Probit models are developed to examine the factors influencing the evacuation behaviour of households and drivers. The behavioural responses that emerge from the survey provide important factors to be considered in mitigating the impact of tornadoes at the individual level as well as the community level. The total time consumption from the warning issuance point to the evacuation completion point is analyzed by combining the time distribution of the network and the evacuation time distribution developed based on the survey data. The comparison of the probabilistic time estimates obtained from the resultant distribution with the warning lead time of around 10 minutes indicates why it is imperative to improve the warning lead time. The forecasters’ warning decision-making and the public’s decision to respond to a warning is analyzed using the decision tree approach. A logical basis for the warning decision-making is developed and a fundamental inequality of decision making for issuing tornado warnings is identified. False warning and missed event probabilities are also analyzed using the data from the Canadian Prairies. Further, the underlying factors for false warnings and missed events are analyzed in detail. The overall analysis provides important suggestions to improve the warning performance. The research contributes to a deeper understanding of the tornado detection, warning and communication system by providing an overall analysis that spans across different areas under the general umbrella of tornado disaster mitigation. A set of recommendations are offered as guidelines for consideration and possible adoption by stakeholders who are involved at different stages of the tornado detection, warning, communication and evacuation process.
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