Fire Danger

Fig. 1 - Evaluation of fire danger

There were pronounced differences in fire danger between subwatersheds in the northern and southern portions of the study area (Figure 1). Support for the proposition of low fire danger was generally moderate in the north and low in the south, which also contained small pockets of very low support. Dangerous wildfire conditions were largely driven by conditions conducive to severe fire behavior. Figure 2 shows the partial products of the entire evaluation process; from viewing this composite, it is possible to see the various contributions to overall fire danger. We summarize the results of the partial products immediately below.

Fig. 2 - Composite of all partial
product evaluations

Fire Hazard

Throughout much of the northern half of map zone 16, evaluation of fire hazard showed moderate to full support for the proposition of low fire hazard. The outstanding exception was the northern peninsula of subwatersheds extending to the east, where most of the subwatersheds showed low support for the proposition (Figure 2). Likewise, in much of the northern half of the map zone, evaluation of fire regime condition class showed moderate to full support for the proposition of low departure of vegetation and fuel conditions from historical ranges. The southern half was mixed in its support but with a considerable number of subwatersheds showing low, very low, and no support.

The canopy fuels evaluation was composed of the partial evaluations of canopy bulk density and canopy base height. In general, the canopy fuels evaluation showed subwatersheds displaying conditions favorable to severe wildfire in both the northern and southern portions of the map zone. Evaluation of canopy base height showed conditions conducive to severe wildfire in the northern peninsula of subwatersheds extending to the east and especially in the southern subwatersheds. Evaluation of canopy bulk density showed conditions favorable to severe wildfire throughout the map zone, but most especially in the northern peninsula of subwatersheds extending to the east.

The surface fuels evaluation was composed of the partial evaluations of fire behavior fuel model and fuel loading. In general, the surface fuels evaluation showed subwatersheds displaying conditions favoring severe wildfire in both the northern and southern portions of the map zone, but most especially in the northern peninsula of subwatersheds extending to the east (Figure 2). Here, fuels were dominated by shrub types with grassland-savanna fuel types also common. Evaluation of fire behavior fuel model showed that with the exception of the northernmost peninsula of subwatersheds extending to the east, the northern half of the map zone showed moderate to full support for the proposition that expected fire behavior would be low. In the subwatersheds of the southeastern portion of the map zone, the evaluation suggested that expected wildfire behavior would be severe. The evaluation of fuel characterization class showed highly mixed results throughout the map zone, with the exception of the northernmost peninsula of subwatersheds extending to the east where surface fuels were conducive to severe wildfire.

Fire Behavior

The fire behavior evaluation consisted of the partial product evaluations of fire spread rate, flame length, fireline intensity, and crown fire potential (Table: Logic outline, Figure 2). Throughout the map zone, there was low to very low support for the proposition that expected wildfire behavior would be low.

The evaluation of wildfire spread rate showed that expected spread rate of surface fires would be high under 90^th percentile conditions especially in the central and northern sectors. In the flame length evaluation, the likelihood of high flame length was high in the southern half of the map zone and in the southernmost peninsula of subwatersheds extending to the east in the northern sector. The evaluation of fireline intensity produced results similar to those of the flame length evaluation, and crown fire potential results were similar to those of the spread rate evaluation (Figure 2).

Ignition Risk

The ignition risk evaluation consisted of the partial product evaluations of the Palmer Drought Severity Index, the Keetch-Byram Drought Index, NDVI-relative greenness, and the relative number of cloud-to-ground lightning strikes. Throughout the southern half of the map zone, there was low support for the proposition that likelihood of wildfire ignition is low. In general, higher overall ignition risk was driven by the tendency for more severe annual summer drought and lower relative greenness in the southern portion of map zone 16, and moderate to full support for relatively fewer lightning strikes in the northern and central sectors of the map zone.