Side-by-side tree and house damage in the May 2013 Moore, OK EF-5 tornado: Lessons for the Enhanced Fujita scale
Residential (FR12) EF-scale damage categories were obtained from the Norman, Oklahoma NWS Forecast Office storm surveys as reported in the online Damage Assessment Tool. Tree damage was estimated visually using several sources of aerial post-tornado imagery. For homes with a known EF-scale rating, damage characteristics of nearby trees (i.e., within 20 m) were recorded, subject to clarity and resolution constraints of the imagery. Tree damage was clearly less in the vicinity of EF-1 or EF-2 homes, compared to EF-4 or EF-5 homes. However, there appear to be no trends to support assignment of tree uprooting versus trunk breakage to different wind speed classes as is currently done in EF-scale damage assessments. While this method could resolve differences in tree diameter only to subjective small, medium, or large classes, smaller trees clearly experienced less debarking or removal of all major branches (stubbing) than large trees when near homes with a rating of EF-3 or greater. The current EF-scale tree DIs assign a degree of damage to debarked and stubbed trees that corresponds with inferred wind speeds at the EF-2 and EF-3 levels, but only a small percentage of the trees near EF-2 or EF-3 homes were stubbed. The percentage is much higher for trees near EF-4 and EF-5 homes. These results imply that stubbed and debarked trees are more indicative of EF-4 and EF-5 winds rather than EF-2 and EF-3 winds, supporting the conventional wisdom that this type of damage is indicative of extremely high wind speeds.