The EXPOS model uses a digital elevation model (DEM) to estimate exposed and protected areas for a given hurricane wind direction and inflection angle. The resulting topograhic exposure maps can be combined with output from the HURRECON model to estimate hurricane wind damage across a region.
EXPOS contains two main functions:
The output file is a raster file in GeoTiff format with the following values: 0 = missing data, 1 = protected, 2 = exposed. Output files are named “expos-xxx-yy.tif” where xxx is the wind direction and yy is the inflection angle.
In previous studies, spatial resolutions of 30 or 60 meters and an inflection angle of 6 degrees were found to work well (see below). Note that increasing the inflection angle tends to decrease the size and number of protected areas while increasing the odds that these sites are protected.
The output file is a raster file in GeoTiff format with the following values: 0 = missing, 1 = no damage, 2 = EF0 damage, 3 = EF1 damage, 4 = EF2 damage, 5 = EF3 damage, 6 = EF4 damage, 7 = EF5 damage. Output files are named “hhhh-damage-yy-z.tif” where hhhh is the hurricane ID, yy is the inflection angle, and z is the reduction in EF rating for protected areas.
Note: for large areas, best results will be obtained by converting the DEM to latitude/longitude coordinates (if necessary) before running expos_model and expos_damage and then converting the resulting damage maps to the desired map projection.
Here are the basic steps for using the model. Please see below for more details.
All user functions begin with “expos”. The wind direction and inflection angle must be specified in degrees.
The user specifies a directory (exp_path) for a given study area. Input and output files are stored on the following subdirectories of this directory:
exp_path/dem exp_path/exposure exp_path/damage exp_path/vector
The dem subdirectory contains the input elevation file. The exposure subdirectory contains output files from the expos_model function. The damage subdirectory contains input files from the HURRECON model, the reprojection file, and output files from the expos_damage function. Shapefiles that contain geographic and political boundaries for viewing results are stored on the vector subdirectory.
To run the model, create the above directories, copy the input files to their respective subdirectories, and use the library function to load ExposR.
expos_set_path expos_get_path expos_model expos_damage expos_summarize expos_plot
The expos_set_path function sets the path for the current set of model runs. The expos_get_path function returns the current path. Use expos_set_path before using other functions.
The expos_model function creates a raster file of topographic wind exposure as a function of wind direction and inflection angle.
The expos_damage function uses output from EXPOS and HURRECON to create a raster file of wind damage where topograhic exposure at each location is determined by peak wind direction. If a location is protected, the enhanced Fujita scale rating is reduced by a specfied amount.
The expos_summarize function displays summary information for a specified raster file, including the number of rows and columns, spatial extent, cell height and width, and minimum and maximum value.
The expos_plot function creates a plot of a specified raster file.
expos_set_path("c:/expos/wach_30m") expos_get_path() expos_model(wind_direction=90, inflection_angle=6) expos_damage(hurricane="AL1938-06", inflection_angle=6, protect=2) expos_summarize("dem") expos_summarize("expos-090-06") expos_summarize("AL1938-06-damage-06-2") expos_plot("dem") expos_plot("expos-090-06") expos_plot("AL1938-06-damage-06-2")
The original EXPOS model was written in Borland Pascal and depended on Idrisi for spatial visualization. The model was used in published studies of the ecological impacts of historical hurricanes in New England and Puerto Rico:
Boose, E. R., Foster, D. R., Fluet, M. 1994. Hurricane impacts to tropical and temperate forest landscapes. Ecological Monographs 64: 369-400. doi.org/10.2307/2937142.
Boose, E. R., Chamberlin, K. E., Foster, D. R. 2001. Landscape and regional impacts of hurricanes in New England. Ecological Monographs 71: 27-48. doi.org/10.1890/0012-9615(2001)071[0027:LARIOH]2.0.CO;2.
Boose, E. R., Serrano, M. I., Foster, D. R. 2004. Landscape and regional impacts of hurricanes in Puerto Rico. Ecological Monographs 74: 335-352. doi.org/10.1890/02-4057.