Changing Fuel layer cells for road crossings and fire barriers in an FDS Level Set case?

[engrahernandez]

Hello everyone,

I am working on modeling a small historical Level Set simulation of an recent urban-wildfire that happened in the Texas Panhandle. I am using QGIS, QGIS2FDS, LANDFIRE FBFM13 data, and FDS.

I am still fairly new to working with the Level Set model and FDS, and I have a questions about possibly modifying the fuel raster? In my current level set 1 simulation, roads and some areas classified as urban or nonburnable affect the shape of the simulated burned area. In several locations, the Level Set fire stops or changes direction at these cells, even though post-fire imagery appears to show that the real fire continued into areas on the other side. I understand that this is by design and expected behavior of the simulation and also would not physically model ember transport or spotting. However, I would like to test whether some of the disagreement is caused by the fuel classifications acting as complete barriers. Is it possible to manually reclassify selected pixels in the fuel layer raster?

For example, could I:

Change selected road or urban pixels to the surrounding grass fuel model so the Level Set fire can continue through those locations Change selected grass pixels to barren, urban, or another nonburnable classification to create a simple fire barrier? Use the second approach as rough surrogate for a fire line or other documented suppression action? Would it be better to edit the FBFM13 raster directly in QGIS before exporting, or is there a supported way to modify the corresponding fuel assignments in the pre or post generated FDS input file? I am also wondering whether these classifications must remain fixed for the entire simulation. Can selected cells become nonburnable at a specified simulation time, or would that require restarting the case?

I have attached:

The FBFM13 fuel layer of simulation
Post-fire imagery showing the observed burned area
The part of the simulated Level Set burned area overlaid on the imagery

Any advice on the recommended workflow on if this is possible or for editing selected fuel cells would be appreciated!

Thank you!

[ericvmueller]

It is possible to define custom fuels in a variety of ways (either modifying existing fuel definitions or setting spread rates and wind speed functions manually ...see 17.5 in the User's Guide). You will then have to add the new definition of your fuel type to the fds input file that QGIS generates.

There are many ways this could be done. The simplest way would just be to put the new spread parameters on the SURF line for for the Urban fuel. You can do it directly in the fds file, or you can do it in the landuse definition file so that it is applied automatically by QGIS when generating the file.
You could also define your custom fuel as a completely new entry in the landuse type (with a new index), and then modify the raster layer in QGIS to apply that new index wherever you want to modify the fuel.

For example adding landuse type 999 to the csv file:
999, &SURF_ID='my_custom_fuel' VEG_LSET_ROS_00=0.1 VEG_LSET_ROS_FIXED=T'
should apply a fuel that spreads with a fixed rate of 10 cm/s anywhere there is a pixel index of 999.

I do not think there is any way to modify a fuel definition as a function of time.