FARSITE 4.0 now includes a Post-Frontal Combustion model. Previous versions of FARSITE only modeled the flaming fire front for the simulation. The Post-Frontal Combustion model simulates both flaming and smoldering fire activity behind the flaming front. This allows calculations of heat flux and emissions so that impacts such as smoke production and soil heating can be simulated.
Post-Frontal Combustion requires two optional GIS themes; Duff loading and Coarse Woody themes. Like some other themes these can be entered as constants across the entire landscape. Use Input > Project Inputs to set constants. Also required is a Coarse Woody Profile file, which contains specific fuel profile data for each value in the Course Woody theme.
To utilize Post-Frontal Combustion use the Model > Post-Frontal Combustion command and check the Simulate Post-Frontal Combustion checkbox. The Post-Frontal Calculations are very intensive and will increase the run time of your simulation several times over, so first attempt a short duration simulation.
Simulation-Level distance checking is required if the simulation includes post-frontal combustion. FARSITE will automatically use Simulation-Level distance checking if post-frontal combustion is enabled. When the Simulate Post-Frontal Combustion checkbox is cleared a dialog box appears with a choice to return to Fire-Level distance checking.
Never Combine Surface and CWD fuels - Use this option when surface fuels are already included in the Course Woody Profile file.
Always Combine Surface and CWD fuels - Use this option when the surface fuels are NOT included in the Course Woody Profile file.
Use Surface Fuels when CWD absent - Use this option when the surface fuels in the fuel Model are the best information available
The combustion history and its numerical integration is more detailed under the High Precision setting, meaning a slightly longer computation time and more precise solutions.
When the Post-Frontal Combustion model is selected the simulated fire displayed in the "LANDSCAPE" window is changed to show fire activity behind the flaming front.
The combustion zone is color coded to show energy release, colors range from yellow (greatest) through orange, red, maroon, and black (least).
The simulation area where combustion is finished is displayed as a darker shade of the visible theme color. Fuels from the Course Woody Profile (.CWD) File have finished burning. Some fuels such as stumps and buried logs, which are not modeled, will be still burning in an actual fire. Sometimes with screen redraws portions of the zone where combustion is finished will turn clear and return to the visible theme colors. This does not indicate a change in post frontal combustion, it is just the way the simulation is redrawn once post frontal combustion is completed for a time step.
Raster maps of heat and emission production can be produced while the simulation is suspended by using the Output > Combustion Maps command.