An Evaluation of Mortality Rates Within thePath of Well-Warned Significant Tornadoes

National Weather Service WFO Detroit, MichiganJoseph V Clark Joseph.V.Clark@noaa.gov

Richard Wagenmaker Richard.Wagenmaker@noaa.gov

• Quantify a key aspect of the impact of violent tornadoes on society (mortality rate)

• Dispel myth that the high death toll associated with the Joplin EF-5 was due to warning failure or other unexpected factors

• Put success of modern warning system in perspective by calculating mortality rate for a historic case and comparing to recent violent tornadoes

Motivations

Hypotheses

• The mortality rate associated with the Joplin, MO EF-5 was typical of violent tornadoes. The high death toll was a function of population.

• Using mortality rate as a metric, the warning system is similarly effective across several examples of modern day violent tornadoes.

• The mortality rate associated with the unwarned Flint-Beecher (1953) tornado (116 fatalities) will be much higher than that of modern day violent tornadoes, including Joplin.

Methodology

• Determine mortality rate using two independent methods (one by each author):

• Method 1: Calculate population affected by the EF4+ portion of the wind field using storm survey data, Census block population data, and basic spatial analysis. Use final death toll to calculate the mortality rate.

Methodology

• Determine mortality rate using two independent methods (one by each author):

• Method 1: Calculate population affected by the EF4+ portion of the wind field using storm survey data, Census block population data, and basic spatial analysis. Use final death toll to calculate the mortality rate.

• Method 2 (when possible): Calculate population affected using houses sustaining EF4+ damage and Census population per household. Use final death toll to calculate mortality rate.*

*Limited Data Availability

Method 1Spatial analysis to estimate population inside the EF-4+ wind field

Path of EF4+ damage (grey shaded)

Census block 1 Census block 2

Census block 4 Census block 3

Population: 100

Impacted: 100

Population: 100

Impacted: 100

Population: 100

Impacted: ?

Population: 100

Impacted: ?

Example

Method 1Spatial analysis to estimate population inside the EF-4 wind field

Population: 100

Impacted: 100

Population: 100

Impacted: 100

Population: 100

Impacted: 50

Population: 100

Impacted: 50

Impacted population: 300

Example

Calculate percentage of overlap (say 50%)Assume evenly distributed population

Method 1Spatial analysis to estimate population inside the EF-4 wind field

Method 2Direct estimation from storm survey using U.S. Census data

Survey information courtesy of NWS WFO Springfield

Number of houses destroyed: xx

People per house: xx

Mortality rate: xx

Fatalities: 158

Events AnalyzedGreensburg, KS EF-5 (2007)

Survey information courtesy of FEMA

Mortality Rate

Fatalities: 11Method 1: 1.6%Method 2: 1.3%

Events AnalyzedHackleburg, AL EF-5 (2011)

Survey information courtesy of NWS WFO Birmingham

Mortality Rate

Fatalities: 18Method 1: 3.1%Method 2: N/A

Events AnalyzedMoore, OK EF-5 (2013)

Survey information courtesy of NWS WFO Norman

Mortality Rate

Fatalities: 23Method 1: 1.6%Method 2: N/A

Events AnalyzedJoplin, MO EF-5 (2011)

Survey information courtesy of NWS WFO Springfield

Mortality Rate

Fatalities: 158Method 1: 1.5%Method 2: 1.7%

Events AnalyzedSmithville, MS EF-5 (2011)

Survey information courtesy of NWS WFO Memphis

Mortality Rate

Fatalities: 15Method 1: 1.6%*Method 2: N/A

ResultsSimilar results yielded by both methods

*Due to lack of information, assumes every fatality occurred in Smithville

Population Center Fatalities Warned Method 1 Method 2

Greensburg, KS (2007) 11 Y 1.6% 1.3%

Hackleburg, AL (2011) 18 Y 3.1% N/A

Moore, OK (2013) 23 Y 1.6% N/A

Joplin, MO (2011) 158 Y 1.5% 1.7%

Smithville, MS (2011) 15 Y 1.6%* N/A

ResultsSimilar results yielded by both methods

• The mortality rate of 1.5% associated with the Joplin EF-5 is on par with other recent violent tornadoes, including the Greensburg EF-5, often cited as a success story of the warning system

• Mortality rates across several examples fell between 1.5% and 3%

*Due to lack of information, assumes every fatality occurred in Smithville

Population Center Fatalities Warned Method 1 Method 2

Greensburg, KS (2007) 11 Y 1.6% 1.3%

Hackleburg, AL (2011) 18 Y 3.1% N/A

Moore, OK (2013) 23 Y 1.6% N/A

Joplin, MO (2011) 158 Y 1.5% 1.7%

Smithville, MS (2011) 15 Y 1.6%* N/A

Events AnalyzedHistorical case: Flint-Beecher EF-5 (1953)

Mortality Rate

Fatalities: 116Method 1: 6.8%Method 2: 10%

ResultsSimilar results yielded by both methods

Population Center Fatalities Warned Method 1 Method 2

Greensburg, KS (2007) 11 Y 1.6% 1.3%

Hackleburg, AL (2011) 18 Y 3.1% N/A

Moore, OK (2013) 23 Y 1.6% N/A

Joplin, MO (2011) 158 Y 1.5% 1.7%

Smithville, MS (2011)* 15 Y 1.6%* N/A

Beecher, MI (1953) 116 N 6.8% 10%

• The 6.8% mortality rate associated with the Flint-Beecher tornado supports the hypothesis that the modern warning system has resulted in a drastic reduction in fatalities associated with violent tornadoes.

• Data was insufficient to include other historic cases such as Waco (1953) or Worcester (1953).

*Due to lack of information, assumes every fatality occurred in Smithville

Conclusions

• The mortality rate associated with the Joplin, MO EF-5 was within normal limits based on a comparison with several recent violent tornadoes. The death toll is therefore confidently attributed to the high population.

• The mortality rate for several violent tornadoes is similar. It ranges from around 1.5% to 3%, an indication that the warning system has been similarly effective across several episodes of violent tornadoes.

• Comparison to Flint-Beecher (1953) indicates about a significant reduction in death toll due to violent tornadoes due to the modern warning system.

References

Federal Emergency Management Agency. Tornado Damage Investigation for Greensburg Kansas. http://www.fema.gov/media-library-data/20130726-1646-20490-3544/greenburg_ks_tornado_damage.pdf . 1 March, 2014.

Hackleburg (Marion County) EF-5 Tornado April 27, 2011. http://www.srh.noaa.gov/bmx/?n=event_04272011hackleburg. 1 March, 2014.

The Tornado Outbreak of May 20, 2013. http://www.srh.noaa.gov/oun/?n=events-20130520. 1 March, 2014.

Joplin Tornado Event Summary. http://www.crh.noaa.gov/sgf/?n=event_2011may22_summary. 1 March, 2014.

Smithville, MS EF-5 Tornado. http://www.srh.noaa.gov/meg/?n=apr2011toroutbreaksmithville. 3 March, 2014.

The Flint-Beecher Tornado. http://www.crh.noaa.gov/dtx/stories/talesjun.php. 12 March, 2014. Beecher 50th Anniversary Commemoration. http://www.crh.noaa.gov/dtx/1953beecher/video.php. 13 March, 2014

For questions and additional information:NWS Detroit/Pontiac, MI

Joseph.V.Clark@noaa.govRichard.Wagenmaker@noaa.gov

Comments or Questions?

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