Enhanced Fujita Scale (EF-Scale)

On April 1, 2013, Environment Canada’s Weather Service introduced a new scale to measure the intensity of wind damage. This scale, called the Enhanced Fujita Scale or EF-Scale, is a more modern and improved version of the original Fujita Scale (F-Scale).

As with the original scale, the EF-Scale is a 6-point scale that goes from zero (weakest) to five (strongest). Its adoption unifies the approach to wind damage assessment in Canada and the United States.

Environment Canada used the F-Scale to rate wind damage, in particular tornado damage, for several decades. However, the F-Scale, developed by Prof. T. Fujita in the 1960’s, was found to have significant shortcomings. There was a limited number of damage indicators with which to rate damage, and engineering studies had shown that the F-Scale wind speeds were not well correlated with actual damage.

The EF-scale employs a large number of damage indicators, ranging from residential housing to office towers to trees. Wind speeds are more accurately related to wind damage thanks to an expert elicitation process that involved the meteorological, engineering and architecture communities. The damage ratings are also backwards compatible with the original F-Scale; only the associated wind speeds have undergone major changes.

The EF-scale was adopted by the United States in 2007. EC had been evaluating the scale and its use in the US since that time. Based on that evaluation, a number of minor revisions were made so that the EF-Scale is better suited to the Canadian context. EC uses 31 damage indicators and a wind speed scale that ranges from 90 km/h (low end of EF0) to more than 315 km/h (high end of EF5).

The EF-scale wind speeds and comparison to the original F-scale wind speeds are shown below.

Table 1. Comparison of F-Scale and EF-Scale Wind Speeds
F/EF RatingF-Scale Wind Speed
Rounded to 10 km/h
EF-Scale Wind Speed
Rounded to 5 km/h
060-11090-130
1120-170135-175
2180-240180-220
3250-320225-265
4330-410270-310
5420-510315 or more

Table 1. Comparison of F-Scale and EF-Scale wind speeds (adapted for Environment Canada) associated with damage ratings. Note that for the EF-Scale wind speeds have been increased for lower ratings and decreased for higher ratings.