Geoscience Reference
In-Depth Information
Because of the limitations of the original 13 standard fuel models, some fire
behavior models (such as the ones discussed later in this chapter) allow users to cre-
ate custom fuel models that better capture the structures being modeled. Meanwhile
there has been considerable effort to develop a new extended set of fuel models that
can better capture the full extent of fuels we might find in the field without establish-
ing an infinitely expansive set of models. One commonly used such classification is
a new set of 40 fuel models that are an extension of Anderson's original 13 (Scott
and Burgan
2005
).
Understanding and mapping fuels remains a complicated and elusive activity.
Any set of models will underrepresent the variability in the landscape and there is
no obvious “correct” pixel size or mapping-unit for analyzing fuels or for mapping
the underlying terrain. Even massive governmental efforts (such as the LANDFIRE
project) using satellite data to map regions into the standard 13 fire behavior fuel
models tend to provide controversial results (Aplet and Wilmer
2003
; Provencher
et al.
2009
).
3.4.1 Intensity
Fire intensity theoretically refers to the amount of energy released by the process of
combustion. Therefore, it would seem natural that this important constituent of fire
regimes would be quantified and mapped in some measure of energy released per
unit area over a specific amount of time. But wildland fire is complicated. In many
large fires, thermal sensors, both on the ground and airborne, are used to identify
and map hotter parts of the fire. Rather than mapping extreme fire behavior and the
hottest temperatures, these tools tend to be used at night to identify areas that have
remained hot after the passage of the flaming front of a fire. These are the areas
fire fighters worry about extinguishing to avoid further spread of the fire during the
following afternoon or in future windy conditions.
Researchers interested in fire behavior might instead be concerned with map-
ping the internal patterns of fire intensity or perhaps modeling future fire intensity.
Depending on their ecological focus they may be interested in the peak tempera-
ture reached when the initial flaming front passes or they may be more interested
in the length of time the soil was exposed to certain temperatures during the glow-
ing combustion or smoldering phase of fire, which may continue for hours after the
flame front passes, resulting in significant changes to the organic materials in soils.
However, such measurements are problematic in the field. Therefore, flame height,
flame length, or even the rate at which the fire spreads are often used as proxies for
the energy released by fire.
Unfortunately, such measures are only able to be tied to specific amounts of
energy released when they are tied to specific fuel configurations (Cheney
1990
).
Also, there is no single system or nomenclature for estimating the intensity of a
wildland fire after it has burned. Therefore, analysts tend to look at the degree of
change seen on the landscape after the fire to map the associated fire intensity.
