Terrain Influences on Tornado Hazard in the Southeast across 25 years (1990-2014)

There is increasing recognition of the potential influence of terrain on tornado formation, movement, and behavior, but few attempts to use large database records to investigate such influences.  In this study, >3000 tornado database records are combined with digital elevation models to examine the influence of terrain on tornadoes in the Southeast (TN, MS, AL, GA, NC, and SC).  Primary questions were, “Are southeastern tornadoes:”  “1) longer or shorter when traversing rough terrain?”; “2) in more or less rugged terrain than unaffected areas nearby?”; and “3) in rugged terrain typically more or less intense than those in less rugged terrain?”.  We combined tornado records for the focal states during the period of 1990-2014 and 10-m digital elevation models (DEMs).  Tornado start and end points, and a mean track width (50 m) were combined to define polygons of the tornado tracks, and overlaid on the DEMs.  To test whether observed tornado tracks were more or less rugged than nearby locations, the start and end points of each observed tornado were shifted 2 km and 5 km (separate analyses) to the east, west, north and south, to develop a distribution of terrain variability available in the region. This was then used to compare to observed variability of each tornado’s path. In addition, elevation variability in 0.5 degree (lat, long) squares was regressed against total tornado track length in each square to test for a terrain effect on track lengths.  Spatial and tabular databases were created and will be used in future studies to predict areas that may be more prone to tornado activity.