Influence of spatial inhomogeneity of tornado occurrence on estimated tornado hazard

Abstract

Tornado hazard assessment is often based on the consideration that the spatial distribution of tornado occurrence is homogeneous in a region. Although this assumption simplifies the analysis, it could overestimate and underestimate tornado hazard for regions with lower and higher tornadic activity if an average rate of tornado occurrence is employed. The degree of overestimation and underestimation is unknown. This study is focused on the assessment of the impact of spatial inhomogeneity of tornado occurrence on the estimated tornado hazard and the development of tornado hazard maps for southern Ontario. The results indicate that at the factored design wind speed the exceedance probability for tornadic winds is much smaller than that for synoptic winds, even if the spatial inhomogeneity of tornado occurrence is considered. Furthermore, the results show that the spatial inhomogeneity of tornado occurrence has significant impact on the spatial tornado hazard level, that the return period values of tornado wind speed vary significantly over the considered region, and that the inhomogeneity must be considered in developing probabilistic quantitative tornado hazard maps.