--- NESL, the NCAR
      Earth System Laboratory ---

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.


                                                                                                                                                                    

Simulation of
          the evolution of a fire line with CAWFE, NCAR's Coupled
          Atmosphere - Wildland Fire - Environment model. 

Animation - click here for .avi (55 Mb)
Animation - click here for .mp4 (3 Mb)


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.

Vertical
          vorticity (i.e. the rotation around a vertical axis) - red is
          positive, blue is negative. Animation - click here for avi


The simulations were visualized using Vis5D.


Keywords:  wildfire models, fire behavior, forest fires, fire model, wildland fire model