 |
|
|
INTRODUCTIONEvery year tens of millions of dollars are spent suppressing wildfires and protecting resources and human life. In response to this escalating threat, the Western Governor's Association has recommended that a national hazard and risk assessment be developed and implemented, focusing particularly on the wildland-urban interface (NFPA, Wildfire News and Notes, 1995). The wildland-urban interface is the transition zone between urban development and the surrounding unurbanized landscape. Almost every part of the nation has an interface problem, and the situation is only getting more complex (Davis, 1990). In a time of agency downsizing and broad-based management, GIS applications in fire mangement are timely and extremely useful.
OBJECTIVESThe purpose of this project is to outline an effective, proactive wildland fire assessment method and develop one portion of it. Ideally, a comprehensive assessment method would evaluate risk, hazard, and value and then combine these elements to identify high and critical fire danger areas (see figure 1). Because of our limited GIS capabilities and class deadlines, this project will only develop one component of the assessment method--the hazard map.
Figure 1
 |
Hazard is defined as "the amount of available fuel that can burn and contribute to the spread and intensity of a wildfire, given an ignition source" (Wakimoto and Close, 1993). The following derived or constructed layers were used to create the hazard map: topography, aspect, slope, vegetation, insect and disease. If time had permitted we would have also combined these layers with an evapo-transpiration (precipitation and temperature) layer.
The project area is the greater Logan Ranger District (20 quads), which extends from the Wellsville Wilderness Area (west) to Bear Lake (east) and the Utah-Idaho border (north) to south of Blacksmith Fork Canyon.
The lattice was built from DEM's.
Figure 2
The shaded relief was built using the lattice in GRID.
Figure 3
The aspect map was created using GRID and the following reclass table:
-2 -1:1 0 22.5:360 22.5 67.5:45 67.5 112.5:90 112.5 157.5:135 157.5 202.5:180 202.5 247.5:225 247.5 292.5:270 292.5 337.5:315 337.5 360:360
Figure 4
Aspect Map
The slope map was created using GRID and the following reclass table:
Lattice Map
Shaded Relief Map
0 10:1
11 20:2
21 30:3
31 40:4
41 81:5
Figure 5
Slope Map
Aspect and slope were combined using following matrix:
ASPECT
N NE E SE S SW W NW
SLOPE
1 4 3 3 3 2 2 3 4
2 3 2 2 2 1 1 2 3
3 3 2 2 2 1 1 2 3
4 3 2 2 2 1 1 2 3
5 3 2 2 2 1 1 2 3
Vegetation (figure 6) was combined with aspect and slope based on the fuel and fire behavior characteristics of the vegetation. For example, if a conifer stand was on a north aspect with a slope of 0-10 (1), it would receive a low hazard rating (4). However, if that same stand was on a 50-degree (1) south aspect, it would receive a much higher factor weighting (2 or 1), because of changes in fuel moisture, vertical arrangement, and horizontal continuity.
Figure 6
Vegetation Map
The insect and disease data was obtained from Boise Pest Management and overlaid on the combined aspect, slope, and vegetation map to produce the hazard map.
Figure 7
Insect and Disease Map
Figure 8
Hazard Map
CONCLUSION
