LSFIRE

LSFIRE is a level-set wildland fire spread model built on AMReX, in erf-model/LSFIRE. It uses Rothermel surface spread, an elliptical fire-front model, and an ELMFIRE-style narrow band to advance the fire perimeter.

The repository includes the fire engine and a pinned upstream ERF submodule. See the LSFIRE user documentation for build instructions, a quick start, and input options.

How LSFIRE maps to ERF

Coupling item	In LSFIRE
Engine directory	FireEngine/
Registration	ERF_REGISTER_FIRE_ENGINE(FireELMFIRE, "lsfire") in ERF_FireELMFIRE.cpp
Selection	erf.fire.engine = lsfire, with erf.fire.enable = true
Build	ERF_ENABLE_FIRE=ON and ERF_FIRE_ENGINE_DIRS=/path/to/LSFIRE/FireEngine
Adapter	FireEngine/ERF_FireELMFIRE.*, with fuel and ignition readers
Model core	FireEngine/LSFIRE/include and FireEngine/LSFIRE/src
Atmospheric coupling	ERF’s Source/FireCoupling, in the ERF/ submodule

The engine is compiled into erf_exec with ERF’s own AMReX. There is no separate libelmfire_core.a to build or link. ERFFireEngine.cmake and Make.package provide the CMake and GNU make hooks. The ELMFIRE names in the adapter and core are retained implementation names; the registered engine name is lsfire.

Fire engine contents

Part	Where	What it does
ERF adapter	FireEngine/ERF_FireELMFIRE.*	Sets up the LSFIRE hierarchy on ERF’s fire grid, passes wind and terrain to the core, and returns time-averaged fluxes
Fuel and ignition readers	FireEngine/ERF_FireReadFuel.cpp, ERF_FireReadIgnition.cpp	Read LANDFIRE fuel IDs and area-ignition masks from NetCDF
Model API	FireEngine/LSFIRE/include/ELMFIRE_API.H	Exposes the core configuration, advance, and field access
Fire hierarchy	FireEngine/LSFIRE/src/Core	Manages fire levels, time stepping, ignition, and output
Spread physics	FireEngine/LSFIRE/src/Physics	Rothermel spread, fuel models, elliptical front velocity, and optional spotting
Front propagation	FireEngine/LSFIRE/src/Numerics, FireEngine/LSFIRE/src/DataStructures	Limited gradients, second-order Runge–Kutta integration, and narrow-band data

These are fire-model components. The atmospheric source placement, Exner conversion, and smoke injection belong to ERF’s shared coupling, described in Fire–Atmosphere Coupling in ERF.

Wind and heat exchange

The engine has two wind modes:

Input	Wind used by the fire
fire.mode = constant_wind	Prescribed fire.constant_wind_u/v, interpreted as the 20-ft wind
fire.mode = atmospheric	ERF’s lowest-cell wind (k = 0), with its height above the local ground; the core converts it to the 20-ft wind using a log law

The atmospheric wind is copied to the fire cells covered by each ERF cell and held fixed during a fire update. It adds no sub-cell wind structure. fire.atmos_wind_height can override the actual height for idealized tests.

The fire takes internal CFL steps to reach the end of the update. The adapter accumulates sensible heat and water-vapour mass flux over those steps and returns their time averages. Sensible heat is returned in W/m²; the water-vapour mass flux is multiplied by ERF’s latent heat of vaporization to return latent heat in W/m². The current core assigns 75% of the burning-cell reaction intensity to sensible heat and 25% to latent heat.

With erf.fire.coupling_type = passive, fire heat and moisture do not feed back to the atmosphere. With lagged, ERF injects the returned fluxes during the next atmospheric step. Heat placement and smoke are controlled by erf.fire.* inputs; the engine’s model inputs remain under fire.* and fire_amr.*.

Repository layout

Item	Where	Purpose
ERF	ERF/	Pinned upstream submodule containing the atmosphere and shared fire coupling
Build scripts	Build/	CMake build script and a Perlmutter environment setup
Coupled cases and tools	Exec/RegTests/LSFIRE/	Input files, fuel table, plotfile reader, and heat-feedback budget checker

The build script enables NetCDF. The Perlmutter environment script is specific to that machine; other systems need their own compiler and dependency setup.

Coupled regression tests

The coupled-test README records reference comparisons with one MPI rank:

Case	What it checks
inputs_lsfire_constant_wind	Agreement with standalone LSFIRE on the same 10 m fire grid at 1 h and 6 h
inputs_lsfire_atmos_wind	Transfer of ERF’s lowest-cell wind and its height to the fire grid
inputs_lsfire_heat_feedback	Lagged sensible-heat and water-vapour budgets, using ERF’s default exponential heat profile and Exner conversion

The coupled-test README gives the reference values and instructions for running the heat and moisture budget checker.

Model description paper

Liu, Y., Huang, H., Saltiel, T. M., Feng, S., Coleman, A., and Almgren, A. (2026). ERF-LSFIRE v1.0: Coupling a Level-Set Fire Model with the Energy Research and Forecasting Model for Fire-Atmosphere Simulations. EGUsphere preprint. https://doi.org/10.5194/egusphere-2026-5430.