Assessment of tornado hazard for spatially distributed systems in southern Ontario

Tornado hazard assessment for a single critical facility such as a hospital or a power generation station is well established. However, a quantitative tornado hazard assessment for a group of facilities, for a pair of points or areas, or for transmission lines, including consideration of the towers, is not available, although it is expected that an increase in the spatial separation among critical facilities is likely to reduce the hazard for all facilities experiencing the same tornado. This quantitative hazard estimation can be important in order to facilitate and guide disaster mitigation planning. This study is focused on a sensitivity analysis of the tornado hazard considering multiple ‘facilities’ with different orientations, footprints and spatial separations. The tornado hazard is expressed in terms of the annual probability that the maximum gust wind speed due to the same tornado exceeds a specified value at two facilities or transmission line systems. Although the adopted simulation-based analysis procedure is applied to southern Ontario, it is equally applicable to other geographic locations. Numerical results suggest that, in general, the dimensions of the footprint of the facilities can be ignored for large separations. The tornado hazard tends to decrease by one order of magnitude as the separation increases by one order of magnitude. Further, the hazard for at least one point on a transmission line is significantly higher than that for at least one transmission tower on the line.