Relative Wildland Fire Hazard of Idaho

To determine the relative wildland fire hazard for this analysis, fuel hazard, expected fuel moisture (aspect), and slope effect on fire behavior were used. Fire behavior is dependent upon fuels (arrangement, composition, and structure - relatively constant), weather (variable), and topography (aspect/slope constant). For this analysis, relative fire hazard was analyzed excluding the effects of real-time weather condition.   A rating of high displays areas where fires may be more difficult to control.  Relative Wildland Fire Hazard was then derived using the standardize values for fuel hazard, fuel moisture (aspect), and fire intensity (slope):

Relative Wildland Fire Hazard = Fuel Hazard + Fuel Moisture + Fire Intensity/3

At best, predicting surface and canopy fuel loads from mid-scale data is problematic at best.  The structure, composition, and arrangement of fuels are dependent upon the disturbance history of any given stand.  Disturbance history includes natural processes (e.g., fire, wind, insects, and pathogens), as well as anthropogenic processes (e.g., silvicultural treatments and grazing practices).  The only available proxy to the disturbance history (and consequently fuel loadings) available at a mid-scale level is the current structure and composition of vegetation (e.g., cover type, canopy cover, and size class).  Unfortunately, the current structure and composition of vegetation is a very poor predictor of stand history.  For example, stands having the same cover type, canopy cover, and size class may have substantially different histories; one could have been logged and the fuels cleaned up, and the other could have been impacted by mountain pine beetles.

Since the structure and composition of the current vegetation is a poor predictor of fuel loadings, we had Forest Service and BLM fuels specialist assign a very coarse qualitative ranking of "fuel hazard" (e.g., containment problems) to unique combinations of PVT and FBFM.  The specialists considered the following fire behavior attributes when making these assignments: ROS, fireline intensity, the potential for active crown fires, and the potential for spotting.   

For details on how aspect was used to model relative fuel moisture, refer to the metadata for the Fuel_moist GRID

For details on PVT/FBFM/Fuel Hazard, please refer to the metadata for Fuel Hazard

The next step was to develop a relationship between fire intensity and slope using BehavePlus.  We first derived fire intensity values for two fire behavior fuel models (FBFM6 and FBFM10) and the midpoint of four slope classes (5, 20, 45, and 80%).  Values for other variables needed to run BehavePlus for estimating fire intensity are displayed below:

Parameter                                                           Value
1-hr fuel moisture                                                 5%
10-hr fuel moisture                                               6%
100-hr fuel moisture                                              7%
Percent moisture for live woody material                 100%
Mid-flame wind speed                                             5 mph
Wind vector direction                                             0 degrees


Estimates of fire intensity for each fuel model were averaged by slope class, and then standardized between 0.0 and 1.0.  These standardize values were then used to reflect the effects of slope on fire behavior.
Slope       Slope                                                Average        Standarized
Class      Midpoint(%)      FBFM6      FBFM10      Fire Intensity     Fire Intensity 
1                   5                337            217           277                0
2                 20               355            231           293                0.06
3                 45               436            289           363                0.32
4                 80               652            446           549                1


Relative Fire Hazard  was then derived using the standardize values for fuel hazard, fuel moisture (aspect), and slope:

Rel_fire_haz = (FUEL_HAZ + FUEL_MOIST + SLOPEstd)/3

Relative wildland fire hazard was not assigned to agriculture, rock, urban, and water land cover classes since we assumed that wildland fires do not occur on these areas, and also because they were not characterized by a fire behavior fuel model.

No warranty is made by the Bureau of Land Management as to the accuracy, reliability, or completeness of these data  for individual use or aggregate use with other data.

These data were designed to characterize mid-scale patterns across the state of Idaho at a scale of approximately 1:100,000.  The use of these data at scales less than 1:100,000 is not recommended without field verification.

This data set is provided "as-is" without warranty of any kind, including, but not limited to, the implied warranties of merchantability and fitness or a particular purpose.  The user assumes all responsibility for the accuracy and suitability of this dataset for a specific application.  In no event will the creators or USDA Forest Service be liable for any damages, including lost profits, lost savings, or other incidental or consequential damages arising from the use of or inability to use this data set.  Use of these data may require the ability to read ArcInfo Grid datasets.  

Although the resolution of the this theme is a 90-m cell, the expected accuracy does not warrant its use for geographic extents smaller than approximately 10,000 acres.  That is, these data were not designed to be used for "project level" assessments that typically require 1:24,000 scale data.