Sensitivity Analysis of Upwind Fetches for More Accurate Effective Roughness in Landfalling Hurricanes

Accurate modeling of storm structure, intensity and wind field is crucial to develop a state of the art tropical cyclone catastrophe model. However, wind hazard modeling is not complete until the actual surface winds are calculated using a rigorously defined local surface roughness. Once the marine exposure surface wind speeds are modeled, appropriate steps should be taken to estimate the effective surface roughness. One of the most challenging aspects of calculating the effective roughness at a given location is assessing the distance over which the wind is affected by the underlying land surface. This distance, known as fetch, is the starting point in assessing friction and gust factors. In this study, sensitivity tests are conducted using surface winds computed by the new asymmetric parametric tropical cyclone model currently developed at AIR Worldwide. Hurricane wind observations from Automated Surface Observing System (ASOS) as well as data from academic institutions such as Texas Tech University and University of Florida are also used. Data from multiple recent tropical cyclones at various locations with diverse exposures are used in this study. Local roughness is calculated using 2011 data from the National Land Cover Database (NLCD), created by the United States Geological Survey (USGS). The NLCD land use land cover (LULC) classifications are assigned appropriate roughness lengths based on scientific literature. The USGS classifications are provided at 30-meter resolution, which is resampled at a 0.002-degree (220 meter) resolution. Local roughness factors are used to define an effective roughness for a given location.