An Evaluation of Mortality Rates Within the Path of Well-Warned Significant Tornadoes - PowerPoint PPT Presentation

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An Evaluation of Mortality Rates Within the Path of Well-Warned Significant Tornadoes

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  1. An Evaluation of Mortality Rates Within the Path of Well-Warned Significant Tornadoes National Weather Service WFO Detroit, Michigan Joseph V Clark Joseph.V.Clark@noaa.gov Richard WagenmakerRichard.Wagenmaker@noaa.gov

  2. Motivations 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

  3. 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.

  4. 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.

  5. 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

  6. Method 1 Spatial 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

  7. Method 1 Spatial analysis to estimate population inside the EF-4 wind field Example Population: 100 Population: 100 Impacted: ? Impacted: 100 Population: 100 Population: 100 Impacted: 100 Impacted: ?

  8. Method 1 Spatial analysis to estimate population inside the EF-4 wind field Example Calculate percentage of overlap (say 50%) Assume evenly distributed population Population: 100 Population: 100 Impacted: 50 Impacted: 100 Population: 100 Population: 100 Impacted: 100 Impacted: 50 Impacted population: 300

  9. Method 2 Direct estimation from storm survey using U.S. Census data Number of houses destroyed: xx People per house: xx Fatalities: 158 Mortality rate: xx Survey information courtesy of NWS WFO Springfield

  10. Events Analyzed Greensburg, KS EF-5 (2007) Mortality Rate Fatalities: 11 Method 1: 1.6% Method 2: 1.3% Survey information courtesy of FEMA

  11. Events Analyzed Hackleburg, AL EF-5 (2011) Mortality Rate Fatalities: 18 Method 1: 3.1% Method 2: N/A Survey information courtesy of NWS WFO Birmingham

  12. Events Analyzed Moore, OK EF-5 (2013) Mortality Rate Fatalities: 23 Method 1: 1.6% Method 2: N/A Survey information courtesy of NWS WFO Norman

  13. Events Analyzed Joplin, MO EF-5 (2011) Mortality Rate Fatalities: 158 Method 1: 1.5% Method 2: 1.7% Survey information courtesy of NWS WFO Springfield

  14. Events Analyzed Smithville, MS EF-5 (2011) Mortality Rate Fatalities: 15 Method 1: 1.6%* Method 2: N/A Survey information courtesy of NWS WFO Memphis

  15. Results Similar results yielded by both methods *Due to lack of information, assumes every fatality occurred in Smithville

  16. Results Similar 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

  17. Events Analyzed Historical case: Flint-Beecher EF-5 (1953) Mortality Rate Fatalities: 116 Method 1: 6.8% Method 2: 10%

  18. Results Similar results yielded by both methods 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

  19. 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.

  20. 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

  21. Comments or Questions? Thank you. Comments or Questions? For questions and additional information: NWS Detroit/Pontiac, MI Joseph.V.Clark@noaa.gov Richard.Wagenmaker@noaa.gov