Wednesday, 25 January 2012
Assessing the Magnitude and Societal Impacts of the 25-28 April 2011 Tornado Outbreak in the Southeastern U.S
Hall E (New Orleans Convention Center )
The 25-28 April 2011 tornado outbreak affected a large region of the southeastern U.S. and produced an extraordinary number of strong tornadoes. Preliminary reports suggest that the intensity of this tornado outbreak may be greater than any other outbreak observed in recent history, including the April 1974 super outbreak. In this study, GIS is employed to objectively ascertain the magnitude and societal impact of this outbreak and compare it with other notable tornado outbreaks. Two metrics are developed to estimate the intensity of the outbreaks. First, the collective work of each tornado, specifically the wind force of each tornado multiplied by its track distance, is calculated and summed up to provide a quantitative measure of outbreak intensity. Second, the track distance for each tornado in the outbreak is multiplied by the identified EF intensity level and summed up to provide a more eloquent and simplistic measure of outbreak strength, coined “Fujita miles”. Preliminary analyses indicate that the total work of the tornadoes in each outbreak is very highly correlated with the total Fujita miles.
Several metrics are developed to provide measures of the societal impacts of each tornado outbreak. First, the affected population in each outbreak is estimated by utilizing census block data to approximate the number of people residing within 1 km of each track. This measure is then multiplied by the tornado intensity or Fujita miles and summed to provide an aggregate measure of the tornado outbreak's impact. Secondly, the number of mobile homes is calculated within 1-km of each tornado track and used to approximate the vulnerability of the population affected by the tornadoes in each outbreak. These measures are then compared with the deaths and injuries reported for each outbreak.