Addressing Interconnections between the Built and Natural Environments through Post-Event Damage Surveys

Mitigation research to enhance community resilience to tornadoes to date has focused primarily on increasing the capacity of individual low-rise residential structures in order to reduce damage and debris impacts. Yet no research has systematically discussed the highly interconnected nature of debris and damage propagation in both the built and natural environment and how this contributes to the overall risk to the public from tornadoes.

Preliminary analyses based on damage surveys from the Joplin, MO tornado indicate that at lower wind speeds estimated by a treefall model, shielding from nearby structures is advantageous to structural performance. However, a higher home density, and therefore a higher probability of debris, puts structures at increased risk for catastrophic damage.  This result parallels recent findings that indicate that forest trees are less likely to be damaged in low-intensity tornadoes if they are surrounded by a high density of neighbors compared with trees having fewer neighbors.  The magnitude of this sheltering effect decreases and sometimes even reverses in high-intensity storms.  Thus, a sheltering effect clearly exists in both the built and natural environments such that nearby structures and trees reduce risk, but that benefit vanishes or reverses at extreme wind speeds.

To understand these interactions, a vortex model coupled with a mechanistic treefall model simulates a tornado as it propagates through an interconnected built and natural environment. Fragility curves for structures initiate damage and probabilistic debris flight models simulate debris propagation. Here, model results will be compared to analyses from historical surveys. The investigators hope to carry out field sampling to validate the model results during the 2017 VORTEX-Southeast field campaign.