Enhanced Fujita scale

Enhanced Fujita scale
Name	Enhanced Fujita scale
Introduced	2007
Developed by	Tetsuya Theodore Fujita (original concept), National Weather Service, Wind Science and Engineering Research Center
Used by	United States National Weather Service, Environment and Climate Change Canada, Japan Meteorological Agency (limited)
Scale range	EF0–EF5
Purpose	Classification of tornado damage

Enhanced Fujita scale is a damage-based system used to estimate tornado intensity by correlating observed structural and vegetation damage with wind speed estimates. It was developed to improve upon the earlier Fujita scale by incorporating engineering principles, standardized damage indicators, and collaborations among meteorologists, structural engineers, and forensic wind scientists. The scale is primarily applied by agencies such as the United States National Weather Service, Environment and Climate Change Canada, and has informed international assessments in Japan, Australia, and parts of Europe.

History and development

The Enhanced Fujita scale traces its conceptual roots to Tetsuya Theodore Fujita's work at the University of Chicago and the Stagg Field era of tornado research, which influenced later collaborative efforts involving the National Oceanic and Atmospheric Administration, the National Severe Storms Laboratory, and the Wind Science and Engineering Research Center at Texas Tech University. In the late 1990s and early 2000s, reviews by panels convened by the American Meteorological Society and the National Academies of Sciences, Engineering, and Medicine found discrepancies between Fujita's wind speed assignments and observed structural performance, prompting a multi-institutional revision spearheaded by the National Weather Service and stakeholders including the Federal Emergency Management Agency and the Institute for Business and Home Safety. The result, adopted in the United States in 2007, refined damage descriptions and incorporated guidance from structural engineers associated with FEMA and the American Society of Civil Engineers.

Scale description and rating methodology

The Enhanced Fujita scale assigns ratings from EF0 through EF5 based on post-event damage surveys performed by personnel from agencies such as the National Weather Service, Environment and Climate Change Canada, and local emergency management offices like FEMA field teams. Survey teams evaluate damage indicators developed with input from structural engineers at institutions like Texas Tech University and use standardized charts endorsed by the American Meteorological Society and the International Association of Emergency Managers. Each rating corresponds to an estimated three-second gust wind speed range derived from engineering analysis; for example, an EF3 rating indicates estimated winds sufficient to cause severe damage similar to that discussed in reports by the National Academies of Sciences, Engineering, and Medicine. Investigations often coordinate with law enforcement agencies such as the Federal Bureau of Investigation when events overlap with public safety incidents.

Damage indicators and degrees of damage

Damage indicators (DIs) are specific categories—such as one- or two-family residences, mobile homes, small barns, and large metal buildings—developed with input from organizations including the American Society of Civil Engineers, FEMA, and the Wind Science and Engineering Research Center. For each DI, degrees of damage (DoD) describe progressive failure states from minor loss of roof covering to complete destruction, informed by case studies from events like the Joplin tornado (2011), the Moore tornado (2013), and the Gainesville tornado (1936). Surveyors use DI/DoD matrices to select appropriate indicators, cross-reference with photographic evidence collected by agencies such as the National Weather Service and media outlets like The Weather Channel, and apply consensus-derived wind speed estimates. The methodology emphasizes contextual factors documented in engineering reports from Texas Tech University, Oklahoma State University, and other research centers specializing in severe convective storms.

Differences from the original Fujita scale

Unlike the original Fujita scale conceived by Tetsuya Theodore Fujita—which assigned a single wind speed for each damage level—the Enhanced Fujita scale bases its ratings on multiple damage indicators and refined degrees of damage informed by structural engineering research from the American Society of Civil Engineers and case studies reviewed by the National Severe Storms Laboratory. The EF scale reduced the nominal wind speeds for several ratings, adjusted thresholds to reflect observed building performance in events like the Iowa–Minnesota tornado outbreak (2008), and added detailed guidance on assigning ratings to manufactured homes, schools, and other specific structures cited in FEMA mitigation documents. The change aimed to improve consistency among surveyors from agencies such as the National Weather Service and to align damage interpretation with modern construction practices codified in standards by the International Code Council.

Implementation and usage by countries

The United States National Weather Service implemented the EF scale nationwide in 2007, incorporating training materials from the American Meteorological Society and post-event survey protocols used by the National Weather Service's Storm Prediction Center and local Weather Forecast Offices. Environment and Climate Change Canada adopted the EF scale framework with modifications for Canadian building practices, coordinating with agencies such as Public Safety Canada and provincial emergency management offices. Other countries and institutions, including the Japan Meteorological Agency, researchers in Australia at institutions like the Bureau of Meteorology, and meteorological services in parts of Europe, have referenced the EF methodology in comparative studies but may adapt indicators to local construction norms and standards from bodies such as the International Code Council and regional engineering associations.

Criticisms, limitations, and revisions

Critiques from scholars affiliated with the National Academies of Sciences, Engineering, and Medicine and university research groups at Texas Tech University and Iowa State University note that any damage-based scale is inherently limited by variations in building practices, maintenance, and anchoring. Analyses published following major events like the Joplin tornado (2011) and the Moore tornado (2013) sparked calls from organizations such as the American Meteorological Society and independent researchers to refine damage indicators, improve training for survey teams from the National Weather Service and Environment and Climate Change Canada, and integrate mobile Doppler radar data from projects involving the National Center for Atmospheric Research and the Doppler on Wheels program. Ongoing revisions focus on reducing subjectivity, expanding the DI catalog to include a wider array of structures studied by the American Society of Civil Engineers, and reconciling discrepancies between measured wind speeds and post-storm damage assessments documented in reports by the National Severe Storms Laboratory.

Category:Weather scales