WRF-Fire for Wildland Fire Modeling

WRF-Fire is a physics module within WRF ARW that allows users to model the growth of a wildland fire in response to environmental conditions of terrain slope, fuel characteristics, and atmospheric conditions, and the dynamic feedbacks with the atmosphere.  It is implemented as a physics package with two-way coupling between the fire behavior and the atmospheric environment allowing the latent and sensible heat released by the fire to alter the atmosphere surrounding it, i.e. 'create its own weather'.  It was first released in Version 3.2 (April 2010).

The wildland fire module is currently a simple two-dimensional model of a wildland fire traveling through surface fuels. The module contains representations of:

- The rate of spread of the flaming front

The rate at which the fire front, the interface enclosing the burning region, expands is calculated at points along it using a semi-empirical formula that relates the fire rate of spread as a function of local fuel conditions, wind, and terrain slope.

- A representation of the sub-grid interface between burning and not-yet-ignited fuel

- Post-frontal sensible and latent heat release

* Behind the flaming front, the ignited fuel continues to burn, releasing sensible and latent heat at rates that depend on the size distribution of the fuel particles making up the fuel complex. 

* The sensible heat arises from the heat released during combustion of cellulosic fuels such as grass, shrubs, and tree litter.

* The latent heat arises from the release of the intrinsic moisture in cellulose as well as the fuel moisture content, absorbed by fuels from the atmosphere.

- Exchanges between atmospheric dynamics and fire modules:

* The winds used to drive the fire are interpolated from nearby low-level wind velocities that are themselves perturbed by the fire. 

* Upscaling of heat fluxes to the atmospheric grid scale and distribution in the lowest layers of the atmospheric model

Additional parameters and datasets beyond a standard WRF atmospheric simulation are required.

- The surface fuel available to be burned at each point is categorized using the Anderson classification system for fuel models (3 grass-dominated types, 4 shrub-dominated types, 3 types of forest litter, and 3 levels of logging slash). Each of these fuel categories is assigned a set of typical properties consisting of the fuel load (the mass per unit area) and numerous physical properties having to do with fuel geometry, arrangement, and physical makeup.  The user may make the fuels spatially homogeneous by using one fuel category for the whole domain, alter fuel properties, add custom fuel categories, or (for real data experiments) project a spatially heterogeneous map of fuel categories onto the domain from fuel mapping datasets.

- The user sets the fuel moisture content, an important factor in fire behavior.

- The user sets the number of ignitions, their time, location, and shape.

One time step of the fire model is performed for every WRF time step. The fire model runs on a refined grid, which covers the same region as the innermost WRF domain.  The fire module supports both distributed and shared memory parallel execution.

The Firebrand Spotting parameterization is an optional module for WRF-Fire released in version 4.4 (April 2022). When users opt to generate firebrands, the parameterization identifies areas at risk of fire spotting by modeling the Lagrangian transport and physical processes of individual firebrands throughout the simulation starting at the fire ignition time. The parameterization was designed for high-resolution simulations and tested using large-eddy simulation (LES) in the innermost domain.

See NCAR/RAL's WRF-Fire for Wildland Fire Modeling page for additional information.