The Implementation and Application of the Enhanced Fujita Scale in Canada: An Update

This new version of the EF scale was implemented in Canada in April of 2013. Since that time, the responsibility for wind damage surveying in Canada has moved from Environment Canada to Western University’s Northern Tornadoes Project (NTP, now part of the Canadian Severe Storms Laboratory) and the NTP has continued to make improvements to the EF-scale guidance as our understanding of the impacts of wind on structures and trees has evolved.

Supporting text guidance for several commonly used DIs (e.g. residential housing, trees, electrical transmission lines) has been expanded, and for the Farm Silos and Grain Bins DI both the wind speed guidance and supporting text guidance have received significant updates. The Scalable Box Method used for the estimation of the percentage of snapped and/or uprooted trees with the Trees DI has been documented in detail in an appendix.

Alternative methods for wind speed estimation have also been explored. An appendix has been added describing how in-situ wind measurements made at weather stations hit by tornado or downburst winds can be used to obtain an EF-scale rating. Two other alternative methods are nearing implementation: the estimation of peak wind speed in a tornado using observed treefall patterns with a tornado model, and the estimation of peak wind speed in a tornado using observed debris trajectories and a debris flight model.

When fully implemented, the NTP will be able to use these techniques with new events and for the re-rating of historical events. Given the highest possible EF-scale rating in Canada’s vast boreal forest is typically EF2, the treefall pattern method has the potential to redefine the climatology of F/EF2+ events there. Combined with results from the debris flight model, the potential exists to redefine the F/EF2+ climatology for Canada overall.

Lastly, researchers at the NTP have been involved with the US-led development of a new wind speed estimation engineering standard for use with the EF scale. It is anticipated that this new standard, with minor modifications for the Canadian context, will replace the current EF scale in Canada within the next several years.