February 2008 Super Tuesday Tornado Outbreak Damage Assessment

Amber E. Reynolds1, Richard Krupar2, Tanya Brown1, Anneley McMillan3, Beverley J. Adams3, Daan Liang1, and J. Arn Womble1

1 Wind Science and Engineering Research Center, Texas Tech University 2 Valparaiso University 3 ImageCat, Inc. ABSTRACT The Super Tuesday tornado outbreak began the afternoon of February 5, 2008 and continued until early morning the next day, leaving widespread damage in many states, including Arkansas, Mississippi, Alabama, Tennessee, and Kentucky. This outbreak, with 62 confirmed fatalities, is considered the deadliest since the May 31, 1985 tornado outbreak that affected Southern Ontario, Ohio, Pennsylvania, and upstate New York. This research is based on damage data collected from Madison and Macon counties in Tennessee using the Visualizing Impacts of Earthquakes with Satellites (VIEWS) system developed by ImageCat, Inc. Enhanced-Fujita (EF) Scale damage ratings were assigned to provide detailed per-building damage assessments which indicate various levels of wind force. Preliminary results suggest damage in Madison County, which included the highly publicized damage to Union University in Jackson, was not as extensive as damage in Macon County. These results are derived from a small sample of an entire data set acquired during a four-day ground survey in western and central Tennessee. Future work will include an in-depth examination of tornado damage in relation to certain meteorological storm characteristics to attain a better understanding of how to enhance building resistance and community resilience, minimizing long-term losses. A comparison with National Weather Service tornado damage ratings, as well as with Quickbird and Worldview visible satellite imagery, will be carried out. INTRODUCTION The Super Tuesday tornado outbreak began on the afternoon of February 5, 2008 and continued into the early morning hours of the next day. Figure 1 shows approximate tornado tracks based on radar imagery and storm reports as well as the number of fatalities by state. The EF-Scale is used for rating tornadoes based on the amount of damage that they cause. The scale has the same basic design as the original Fujita scale, using six categories from zero to five to represent increasing degrees of damage. The new EF-Scale takes into account variables such as differences in construction quality. There are 28 Damage Indicators (DI), or types of structures and vegetation, with varying numbers of Degrees of Damage (DOD) that are used to assign EF-Scale ratings to the damage (WISE 2006). Different structures, depending on their building materials and ability to survive high winds, have their own DIs and DODs.

Figure 1. Preliminary tornado tracks and fatalities by state (NOAA 2008). DATA & METHODOLOGY Two weeks after the tornado outbreak occurred, a team deployed to the region and used the VIEWS system to document damage. The VIEWS system is composed of two high-definition (HD) video cameras set up on tripods in the back of a vehicle situated to record structures at the street level. The cameras are connected to a GPS tracking system to collocate recorded damage documentation. VIEWS is a notebook-based system, which integrates GPS-registered digital video footage with high-resolution satellite imagery collected before and after a disaster. After the data were processed, a GoogleEarth file was created to provide georeferenced still images. This analysis provides the first instance of the VIEWS system being used to document tornado damage over a widespread area. Thirty two hours of data were collected. Figure 2 shows several examples from the deployment of the VIEWS system. Previous studies using the VIEWS system include the 2003 Bam, Iran earthquake (Adams et al., 2004a), Hurricane Charley (Adams et al. 2004b), Hurricane Katrina (Womble et al. 2006), the October 2004 Niigata, Japan earthquake (Huyck et al., 2006), the 2004 tsunami (Ghosh et al., 2005) and the 2007 California wildfires (McMillan et al. 2008a).

Figure 2. Deployment of the VIEWS system (Photo courtesy of MCEER Quick Response Report by McMillan et al. 2008b).

In this case, the area of focus was along two long-lived tornado tracks, examining the variability of damage along each length. The damage in Madison County occurred along the same tornado track that impacted Memphis, Tennessee, while the Macon County damage occurred along a second tornado track that occurred farther to the east. For each county, every fourth photo was rated, corresponding to a resolution of approximately 15 meters. Damage Indicators and Degrees of Damage were referenced from the EF-Scale (WISE 2006). MADISON COUNTY Figure 3 shows a GoogleEarth image of the track driven to provide damage documentation in Madison County. Areas in the southwestern portion of the track show varying levels of damage to buildings in and around Union University, including one of only two photos that exhibited EF-4 damage to residence halls on campus. Further to the northeast, single family homes exhibited anywhere from less than EF-0 damage (indicating no damage sustained) to EF-3 damage with most of the walls in the house collapsed, except for small interior rooms.

Figure 3. GoogleEarth image of track driven to document damage in Madison County including pictures of various levels of damage to institutional buildings, low-rise buildings, and single family residences.

MACON COUNTY

Figure 3 shows a GoogleEarth image of the track driven to provide damage documentation in Macon County. Again, damage ranged anywhere from less than EF-0 to EF-4. The damage documented in this county occurred in the small town of Lafayette, Tennessee. Most of the damage occurred to single family residences, with 46 residences sustaining EF-4 level damage.

Figure 4. GoogleEarth image of track driven to document damage in Macon County including pictures of various levels of damage to single family residences. RESULTS & DISCUSSION Figure 5 shows pie charts for the percentage of various levels of damage for Madison and Macon Counties. The percentage of EF-1, EF-0, and less than EF-0 level damage is similar between the two counties. However, the largest differences between the counties can be seen with EF-2 and greater damage. For Madison County, 6% of the damaged documented was rated as EF-2, while 2% of the damage was rated as EF-3. However, only 2 photos out of the 2648 rated were rated as EF-4. For Macon County, 3% of the damage was rated as EF-2, 1% as EF-3, and 3% as EF-4. From these pie charts, the largest difference between these two counties was the increased amount of severe damage, as indicated by an EF-4 rating, which occurred in Macon County. To fully document the results in the aftermath of a natural disaster, especially when considering perishable building damage, a quick response is necessary from damage document teams composed of scientists and engineers. In this study, clean-up

efforts began prior to damage documentation, which sometimes made rating images difficult. The accuracy of any damage assessment declines significantly as the amount of time between the damaging event and the damage documentation increases. In this case, a two week delay occurred in regards to data acquisition.

Figure 5. Pie charts of the percentage of various levels of damage in Macon and Madison County. CONCLUSIONS & FUTURE RESEARCH

The preliminary results of this ongoing research indicate that there was significantly more severe damage, as seen with the increased amount of EF-4 level damage, in Macon County than in Madison County. To further validate this study, a comparison with results obtained by the NWS Nashville, TN office will be conducted in the near future. Future work for this project will include an analysis of damage rating capabilities using satellite imagery obtained after the outbreak. These ratings can be compared with ratings obtained through the VIEWS survey to determine the feasibility of using satellite and aerial imagery for damage assessments. The imagery obtained was for an area covering nearly 26 square kilometers in Madison County, and was purchased from Digital Globe for three dates, using two different platforms. Imagery was obtained on February 10, 2008 from the Worldview 1 satellite; this imagery is panchromatic and offers a 50 cm resolution. Imagery was also obtained on February 8 and March 2, 2008 from the Quickbird satellite; this imagery is panchromatic and multi-spectral, with 60 cm resolution. By selecting imagery captured several days after the event, as well as imagery captured nearly a month after the event, the progress of recovery in the area may be identified by the amount of debris cleanup and rebuilding that has taken place by the time of the last image. In addition, because the imagery is collected from two platforms with different resolution, a comparison of the quality of the images will be possible as well.

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