FLARE

FLARE (Fire-Line Advancement and Reaction Engine) is the fire engine in erf-model/FLARE. It was the native fire model on the ERF-Fire branch of hgopalan/ERF until October 2026.

The FLARE repository is a full copy of ERF plus the engine and other additions. It takes ERF development merges regularly. The FLARE README describes its capabilities and how to build it. This page covers how FLARE maps to ERF, and what its repository holds that is not the engine.

What is inside each repository

How FLARE maps to ERF

Coupling item

In FLARE

Engine directory

FireEngine/

Registration

ERF_REGISTER_FIRE_ENGINE(NativeFireEngine, "flare") in ERF_NativeFireEngine.cpp

Selection

erf.fire.engine = flare, the default in a FLARE build

Build

ERF_ENABLE_FIRE is ON by default in FLARE; it is OFF in ERF

Fire engine contents. The rate-of-spread models, the Huygens and level-set front propagation, fuel and fuel moisture, ignition, acceleration, spotting, crown fire, suppression, structure ignition, and the fire plotfile, statistics and checkpoint.

In the FLARE repository but not in the engine

These items are outside FireEngine/. Some are used by fire runs, but none is part of the engine, and none is in ERF development yet.

Item

Where in FLARE

Inputs

What it does

Tied to fire?

Dust model

Source/Dust, Source/Particles/ERF_DustPC.*

erf.dust.*, ERF_ENABLE_DUST

Emission, settling, deposition and health diagnostics for bare mineral surfaces

No

Fire-dust coupling

Source/FireDust, Source/Dust/ERF_DustFireLofting.*

erf.fire_dust_coupling, erf.fire_dust_crust_reduction, erf.fire_dust_wind_*, erf.fire_dust_lofting_*

Feeds the fire’s burned area, outflow wind and heat flux into dust emission

Yes

MRF fire boost

Source/PBL/ERF_ComputeDiffusivityMRF.cpp

erf.pbl_mrf_fire_thermal_excess, erf.mrf_fire_q_threshold, erf.mrf_fire_t_excess_cap

Raises the convective velocity scale of the MRF scheme with the fire’s heat flux

Yes

Terrain-following inflow

Source/BoundaryConditions/ERF_InflowProfile.*, ERF_BoundaryConditionsInflowProfile.cpp

<face>.inflow_profile = log_law or file, <face>.inflow_profile_file

Looks up the inflow at each boundary cell’s height above its own ground

No

Sounding above ground

Source/DataStructs/ERF_InputSoundingData.H

erf.input_sounding_wind_above_ground, erf.input_sounding_theta_above_ground

Two separate switches that measure sounding winds, or theta, from each column’s ground; with theta, each column is then rebalanced hydrostatically

No

Geostrophic start

Exec/ERF_Prob.cpp

erf.abl_geo_wind

ERF uses this key as forcing only. FLARE also starts the velocity from it, for uniform initialisation with no problem-specific velocity

No

Warm bubble

Source/Prob/ERF_InitCustomPert_ABL.H

prob.bubble_dT, prob.bubble_{x,y,z}_c, prob.bubble_{x,y,z}_r

Adds a theta bubble in the form of WRF’s idealized fire start

No

Building-roof stability

Source/ImmersedBoundarySEB/ERF_IBSEBWallFunction.H

erf.ibseb.stability_scheme = louis, needs erf.ibseb.stability_correction = true

Adds the Louis (1979) stability factors on roofs

No

Imposed surface heat flux

Source/BoundaryConditions/ERF_MOSTStress.H, ERF_SurfaceLayer.*

erf.most.surf_temp_flux with bulk_coeff

ERF has this key for other flux types. FLARE also accepts it with erf.surface_layer.flux_type = bulk_coeff, where it replaces the Ch form of the heat flux

No

Joining fine boxes stacked in z

Source/Utils/ERF_ChopGrids.cpp, Source/ERF_MakeNewLevel.cpp

None

Joins refined boxes stacked in z when a level is made, and checks that column PBL schemes get full columns

No

Cases and tools

Exec/CanonicalTests/{Fire,Dust,Hazard}, Exec/Tools

Fire and dust cases; LANDFIRE fuel map, HRRR winds and map movie scripts

Mostly

The dust model is the largest of these. It uses the same surface-grid design as the fire model, but it runs with ERF_ENABLE_DUST=ON and a fire is not required.

FLARE also has one small addition to the coupling code that ERF does not have: the ERF_FIRE_DEFAULT_ENGINE compile definition, read in Source/FireCoupling/ERF_FireCouplingParams.cpp and set in CMake/BuildERFExe.cmake and Exec/Make.ERF. It lets a build name the engine a deck gets when the deck names none.

This list compares FLARE 690bc4668 with its last common commit with ERF, 6e260ec28, and ERF development at 44c18fd4a, on 2026-10-30. Merges in either direction will change it. To repeat the comparison:

git diff --name-status $(git merge-base upstream/development flare/development) flare/development -- Source

FLARE model documentation

The pages below describe the FLARE fire model and its inputs. They are copied from the FLARE documentation by tools/sync_flare_docs.py; edit them in FLARE and rerun the script.