Topic: On the Implementation of the enhanced Fujita Scale in the USA

[John Allen]

Hi Guys, ive recently recieved a new article concerning the so-called Enhanced Fujita scale and some thoughts on it. I intend to provide a review on its material, which may take me a couple of days. For those who have access or can find access to these things the paper is:
Doswell, Brooks and Dotzek 2009: On the Implementation of the enhanced Fujita scale in the USA. Atmospheric Research, 93, 554-563.

Abstract
The history of tornado intensity rating in the United States of America (USA), pioneered by T. Fujita, is reviewed, showing that non-meteorological changes in the climatology of the tornado intensity ratings are likely, raising questions about the temporal (and spatial) consistency of the ratings. Although the Fujita scale (F-scale) originally was formulated as a peak wind speed scale for tornadoes, it necessarily has been implemented using damage to estimate the wind speed. Complexities of the damage-wind speed relationship are discussed.

Recently, the Fujita scale has been replaced in the USA as the official system for rating tornado intensity by the so-called Enhanced Fujita scale (EF-scale). Several features of the new rating system are reviewed and discussed in the context of a proposed set of desirable features of a tornado intensity rating system.

It is concluded that adoption of the EF-scale in the USA may have been premature, especially if it is to serve as a model for how to rate tornado intensity outside of the USA. This is in large part because its degree of damage measures used for estimating wind speeds are based on USA-specific construction practices. It is also concluded that the USA's tornado intensity rating system has been compromised by secular changes in how the F-scale has been applied, most recently by the adoption of the EF-scale. Several recommendations are offered as possible ways to help develop an improved rating system that will be applicable worldwide.

Anyway, review will follow.
John

[Mike]

So will they revert back to the F scale given this report?  I know Canada still has the F scale but the rest of the planet followed suit even though our building codes are amongst the toughest around so does the EF scale apply still simply because the US codes were perhaps a little lax in considering the EF scale on review?

[Colin Maitland]

Enjoyed that post John, I read

It is concluded that adoption of the EF-scale in the USA may have been premature, especially if it is to serve as a model for how to rate tornado intensity outside of the USA. This is in large part because its degree of damage measures used for estimating wind speeds are based on USA-specific construction practices.

The question is, are you supposed to understand that these tornadoes are calculated on building practices or codes, therefore leading to the conclusion  for example, that due to QLD's cyclonic building code compared to that of say NSW, which has comparatively little tie down and non cyclonic, there is a possible result of more damage in NSW and so therefore could lead to a higher rating on the EF scale? That is taking into consideration that the tornado was of the same wind velocities and characteristics in both states.

I understand that they must consider  "for a building of a certain code, you would need X amount of wind at this speed to cause this amount of damage". One scenario you could have is 2 houses side by side, the same wind speed, for example 90 km/h, but due to a couple of loose fitting tiles, a domino effect takes place and a roof can be lost, the other house has sustained no damage what so ever. There are so many variables that come into play.

That reasoning does not seem take into account all the variables that a tornado could throw at you. My mind instantly went to Japan where some of the rice paper houses still exist in high earthquakes zones. A low scale tornado would thus totally devastate a village and therefore would it gain a higher EF scale? Or most important how could you rate it? Is that the correct way of looking at the EF scale? To me that does not make sense to calculate a tornado on a damage scale compared to direct wind velocity. (The F scale . )

I had never looked at it that way before, that is if I have understood it right. As a builder, you could expose many flaws with this practice of rating. It will be interesting to see the outcome of the report.

If I have got this wrong please let me know.

Thanks

Colin

[Mike]

When will the PDF version become available, John?  Do you have to be a paid member of AMS to view it.  I'd like to read it in earnest!