Correlation of topographic speed-up factors and building damage ratios for Hurricane Fabian in Bermuda

The focus of this study is to use a linear model for boundary layer flow over topography to map the effects of topography on surface wind speeds for Bermuda, and to correlate modeled winds to observed damage to structures. In accounting for the effects of topography on surface wind speeds the standard method is to define a speed-up factor, which then acts as a multiplier on the equivalent surface wind speed above flat terrain. In areas where the speed-up factor is greater, the surface wind speed will be higher, thus one would expect heavier damage to structures.

QuickBird is a high resolution satellite owned and operated by DigitalGlobe. Using a state-of-the-art BGIS 2000 sensor, QuickBird uses remote sensing to a 0.61m pixel resolution degree of detail. Following the landfall of Hurricane Fabian in Bermuda in 2003, the QuikBird satellite captured fine resolution digital imagery of structures on the island, as well as the damage sustained to such structures, mainly in the form of damage to the roof of the building. An algorithm was developed to effectively derive a damage ratio sustained for each building based on the percentage of rooftop covered by a blue tarp, indicating a specific level of structural destruction. This data, coupled with a very detailed building inventory for the island of Bermuda, will be extremely valuable in correlating damage ratios with speed-up factors derived from the topography model.

This is one of the few times that research of this nature has been undertaken with such level of detail. It is expected that this study will lead to a better assessment of uncertainty and limitations of models for understanding speed-up and the associated impact on structures.