Quantification of Wind Speeds in the 19 March 2018 Jacksonville, AL Tornado Through Analyses of Very High-Resolution Tree Damage in a Residential Neighborhood

Efforts are underway to upgrade tree damage indicators in the enhanced Fujita (EF) scale, yet such improvements must necessarily remain categorical and can therefore provide wind speed estimates with only modest precision. More detailed methods are available to use tree damage to estimate wind speeds, although these approaches must be done on a tree-by-tree basis and have substantial data requirements that will seldom be provided from typical post-storm damage surveys. However, surveys in a residential neighborhood following the 19 March 2018 EF3 tornado that impacted Jacksonville, AL allowed the collection of such detailed information on tree characteristics, geographic coordinates, and damage condition for over 100 trees. By feeding these tree characteristics to a coupled wind and tree resistance model, it is possible to determine whether the tree falls at a given hypothetical wind speed. The lowest wind speed required to overcome the resistance of the trunk or root system becomes the minimum (maximum) wind speed estimate at the location of each fallen (standing) tree. When this approach is applied to many trees, it can provide a detailed set of point wind speed estimates at greater precision than is possible using the tree damage indicators of the EF scale. A growing number of studies in recent years have used this or similar treefall-related approaches to generate wind speed estimates in locations where traditional damage indicators are sparse. Maps of wind speed estimates at each tree location plotted alongside the degree of damage determined from more traditional damage indicators within the neighborhood allow a spatial comparison of each type of approach to wind speed estimation.