Remotely Visible Width and Discontinuity of 50 Tornado Damage Paths through Forested Landscapes

Abstract

Tornado damage-path width is a necessary component for calculation of area impacted, which allows estimation of hazards. To date, rarely has variation in damage path width or path discontinuity been a focus. In this paper, using a damage threshold of >25% canopy damage, we quantify width and discontinuity in 50 tornado paths in forested areas. Tornado-path starting and end points were overlaid on Google Earth imagery obtained ≤24 months after the tornadoes, and damage-path width (or absence of damage) was measured for severities >25% canopy loss, at fixed intervals. Width was measured only where both sides of the damage path were clearly defined by forest tree damage, thus many points were excluded from our analysis. Given our threshold level of forest canopy damage, no EF0 tornadoes showed remotely visible damage, and analyses were thus restricted to ≥EF1 tornado paths. Variation in remotely visible damage width was quantified as coefficient of variation, which ranged from 0.227 to 0.852, with a mean of 0.531 among the 50 paths. Discontinuity in remotely visible damage also varied among damage paths; up to 45% of the total number of measured points within a path lacked visible damage. Almost 40% of tornado damage paths exhibited such discontinuity along 20% or more of their path length. We suggest that the long, narrow EF-scale contours (particularly for ≥EF1) often reported after storm surveys may mask extensive width variation in severe damage and substantial portions of tornado paths with no severe damage.