High-resolution observations of microscale influences on a tornado track using Unpiloted Aerial Systems (UAS)

Topography can have a significant influence on tornado intensity and direction by altering the near-surface inflow. However, past research involving topographic influence on tornadoes has shown significant variety in investigative approaches and conclusions. This study uses Unpiloted Aerial Systems (UAS)-based high-resolution imagery, UAS-based 3D-modeling products, and correlation analyses to examine topographical influences on a portion of the 01 May 2018 Tescott, Kansas EF3 tornado. Two new metrics, Visible Difference Vegetative Index (VDVI) gap and (VDVI) aspect ratio, are introduced to quantify damage severity using UAS-based imagery and elevation information retrieved from a UAS-based digital surface model (DSM). Areas of enhanced scour are seen along the track in areas of local elevation maxima. Correlation analysis shows that damage severity, as measured by VDVI gap and VDVI aspect ratio, are both well correlated with increasing elevation. VDVI gap is only weakly correlated with slope, while VDVI aspect ratio is not correlated with slope. These findings are statistically significant at p < 0.05. As the tornado weakened in intensity, the path became non-linear, traversing between two local elevation maxima. It is hypothesized that fast-moving intense flow formed and weakened as elevation increased over the short spatial distance. This research shows topography and surface conditions are two of many important variables that should be considered when performing tornado-damage site investigations. It also illustrates the importance of UASs in detailed tornado analysis. VDVI gap and VDVI aspect ratio can provide insight into damage severity as a function of topography.