Fire Effects

The Fire Effects Index is comprised of two input ratings: values impacted and suppression difficulty. The purpose of the index is to identify those areas that have important values at risk to wildland fire or are costly to suppress, or both.

Values Impacted

Several important values potentially impacted by wildfire were combined into an index for inclusion in the SFRA. These values were also used in the FRA and include: 1) Transportation and Infrastructure Areas, 2) Urban Interface, and 3) Plantations (natural and planted).

The Transportation Infrastructure Effects were created from calculating a 300-m buffer around Levels 1, 2, and 3 roads and a 500-m buffer around elementary and secondary schools, airports, and hospitals.

The Wildland Urban Interface was downloaded from the SILVIS Lab at the University of Wisconsin - Madison. WUI is composed of both interface and intermix communities. In both interface and intermix communities, housing must meet or exceed a minimum density of one structure per 40 acres (16 ha). Intermix communities are places where housing and vegetation intermingle. In the intermix areas, wildland vegetation is continuous, more than 50 percent vegetation, in areas with more than 1 house per 16 ha. Interface communities are areas with housing in the vicinity of contiguous vegetation. Interface areas have more than 1 house per 40 acres, have less than 50 percent vegetation, and are within 1.5 miles of an area (made up of one or more contiguous Census blocks) over 1,325 acres (500 ha) that is more than 75 percent vegetated. The minimum size limit ensures that areas surrounding small urban parks are not classified as interface WUI.

The plantation data were obtained from each individual State. This information was supplemented with a crosswalk from GAP data where available.

Each value impacted input was assigned an impact score by State fire managers using a matrix to assign a value of 1 to 4 (1 being low effect, 4 for high) for each flame length vs. fire size scenarios. To arrive at a score for a value impacted, the individual values in the matrix were summed, i.e., 33. The Values Impacted Rating was determined by summing the Values Impacted Scores for a cell * 100 and dividing that total by the maximum possible score to normalized the result to a value between 1 and 100.

Suppression Difficulty Elements

The Suppression Difficulty Elements are fuel type, topography, and soil type. A fuels layer was used to assign each cell in the State a fuel type of grass, shrub, timber litter, or slash. A topography multiplier was assigned to each of the following slope classes by State fire managers: Slope Class 1 –is 0 – 25 percent; Slope Class 2 is 26 – 40 percent; Slope Class 3 is 41 – 55 percent; Slope Class 4 is 56 – 75 percent, and Slope Class 5 – 76+ percent. Organic/peat (muck) soils were extracted from SURGO data by the States. These soils constitute areas of concern for firefighting efforts, as fires within these areas tend to be expensive and difficult to extinguish.

In arriving at the Suppression Difficulty Rating, suppression costs are evaluated by fuel type and topography. Each burnable cell in the State was assigned a suppression score using a matrix process similar to the one used for the values impacted score. The grass, shrub, timber litter, and slash fuel type scores were based on professional judgment of the State fire managers. The increased difficulty of suppression based on slope was also made. The suppression difficulty score for organic/peat soils was assigned to be 60, which is 1.25 times the maximum score of 48. This higher value is to reflect the increased suppression difficulty in this situation. The Suppression Difficulty Rating for each cell was calculated by multiplying the Fuel Type Score and the Topography Multiplier by the product of the maximum fuel type score and the maximum slope multiplier.

Fire Effects Index

The Fire Effects Index was calculated as the sum of the Values Impacted Rating by 0.68 and the Suppression Difficulty Rating times 0.32. The final Fire Effects Values can range from 0 to 100.