an evaluation of mortality rates within the path of well-warned significant tornadoes national...
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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?
Thank you.Comments or Questions?
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