of Wildland Fire Behavior
The following animations show coupled weather-fire behavior
simulations of the growth of wildfires. They were simulated
using the Coupled Atmosphere-Wildland
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
the fire from behind. The fuel is "chaparral", a brush
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.
As the fire grows, perturbations (seen
next animation to be fire
whirls) grow occur along the fire flank, which are brought
the head, which gets stronger (changing the airflow all around
fire, directing some parts of the fireinto fresh fuel, creating
local heat and more fire whirls, etc. This increase in intensity
due to the environment (which remains constant) or fuel (the
the same throughout the domain), but purely the fire-induced
The simulations were visualized using Vis5D.