Coupled Weather-Wildland Fire Modeling
Simulating
Fundamental
Aspects
of Wildland Fire Behavior
The following animations show coupled weather-fire behavior model
simulations of the growth of wildfires. They were simulated using the Coupled Atmosphere-Wildland Fire Environment
(CAWFE) model.
The widely-observed "universal fire
shape" evolves from the physics of fire interactions with the
atmosphere.
The fire starts as a line; constant easterly winds of 3 m/s are driving
the fire from behind. The fuel is "chaparral", a brush common in
parts
of CA, AZ, and the central Rocky Mtns. Wildfire control in
chaparral (a species that has adapted itself to recurring fires)
is notoriously difficult, because coupling Santa Ana winds, with
droughts, long summers, and (often) steep terrain, creates intense,
rapidly spreading fires.
The misty field is smoke, denser and more red where the fire is burning
most intensely.
As the fire spreads, it evolves into a shape well-known to fire
managers, with three parts: 1) the "head" - the leading edge of the
fire where the heat is focussed, 2) two "flanks" - along the side, here
the winds blow basically parallel to the edge of the fire, and 3) the
"back" - the slowest moving part of the fire that creeps against the
wind. The heat from the fire rises in updrafts(s) that the winds
focus at the head of the fire. These updrafts draw warm air into
their base from all directions, guiding the wind to flow along the
flanks and focus the heat at the front. In this way, the
interaction of the fire with environmental winds creates a
self-perpetuating, universal shape that is observed in fires in many
conditions all around the world.
Animation -
click here for .avi
As the fire grows, perturbations (seen in the
next animation to be fire
whirls) grow occur along the fire flank, which are brought forward to
the head, which gets stronger (changing the airflow all around the
fire, directing some parts of the fireinto fresh fuel, creating some
local heat and more fire whirls, etc. This increase in intensity is not
due to the environment (which remains constant) or fuel (the fuel is
the same throughout the domain), but purely the fire-induced winds.
Animation - click here for
avi
The simulations were visualized using Vis5D.
Keywords: wildfire models, fire behavior, forest fires, fire model, wildland fire model