How accurate is the Fire kit?

People make real decisions about wildfire, so you should know how far to trust a Fire kit result. This page explains what the simulation is built on, how we test it, what it leaves out, and how to read a result safely.

In short: the Fire kit is a planning tool. It is good for comparing places, scenarios and options: which slopes burn fastest, where a fire from a power line would run, how much worse a very dry, windy day is. It is not a forecast of a real fire. Never use it to decide whether to evacuate. For an active fire, follow your local emergency services.

What it is built on

The kit uses the standard fire behaviour science that US land managers use:

• Surface fire: Rothermel's spread model (1972, with Albini's 1976 update), with the 40 Scott and Burgan fuel models and the original 13.
• Crown fire: Van Wagner's model for when a fire climbs into the trees, Rothermel's 1991 model for how fast a crown fire runs, and Finney's method for fires that are partly in the canopy.
• In Canada: the Canadian Forest Fire Behaviour Prediction (FBP) System (Forestry Canada 1992, updated by Wotton and others in 2009), Canada's own model, built from experimental fires in Canadian forests. It works from the fire weather codes Canadian agencies use every day.
• Spread across the map: a minimum travel time method, the same idea used by the US Forest Service's FlamMap. The fire takes the fastest path through every cell, uphill and downwind first.

In the US these are the models behind FARSITE, FlamMap and BehavePlus, the US tools for fire planning; in Canada, the FBP System is the model behind Canada's national fire behaviour maps and Prometheus.

The data under it

How good a result is depends most on the data:

• Fuels (US): LANDFIRE, the national map of fuel types and tree canopy from the US Department of the Interior and the US Department of Agriculture, at 30 m. The lower 48 states use the newest LANDFIRE update, with the previous release filling any gaps. Alaska and Hawaii use their own LANDFIRE releases.
• Fuels (Canada): Natural Resources Canada's national fuel type map (2024), at 30 m: spruce, pine, aspen, mixedwood, grass and the land that does not burn.
• Terrain: Scribble Maps elevation, from USGS 1 m lidar across most of the US and 30 m elsewhere.
• Wind: in the US the kit starts from the National Weather Service hourly forecast for your area; elsewhere from a steady 20 km/h west wind. You can change it to test any wind.

The report card says which fuel data covered how much of your area, and how confident that is. Both maps show fuels as they were when they were made (LANDFIRE 2024 and 2025, the Canadian map 2024). A fire, a harvest, a fuel treatment or new homes since then are not in them.

How we check it

What we test today:

• The fire behaviour math is checked against an independent open source implementation of the same models (Pyretechnics). On flat ground the spread rate, the fire's intensity and its shape match within 0.5%. With wind and slope together they match within 10%, because the two tools combine wind and slope in slightly different ways that are both used in practice.
• The Canadian model is checked against the published Fire Weather Index tables (the Initial Spread Index), and each fuel type's spread, crowning and fuel consumption against the published FBP equations.
• Known shapes: with no wind on flat ground the fire grows as a circle, and with wind it grows into the ellipse the models predict.
• Things that must never happen: wet fuel does not burn, roads, water and rock stop a fire (even crossing them diagonally), and a fire never burns beyond the time you set.
• Real fuel data: when we load a new LANDFIRE release, we check its values at known places (forest, shrub, grass, towns) before the kit uses it.

The model checks are part of our automated tests.

What we are adding (benchmarks):

• Past fires: we re-run real wildfires in the US and Canada with the fuels and weather from before each fire, and compare the simulated burned area with the real fire perimeters (the US national interagency fire records and Canada's National Burned Area Composite). Each score is compared with a simple circle of the same area around the start, so it shows how much better than a guess the model is. We will publish the scores on this page, by fuel type and region.
• FlamMap comparison: the same landscapes run through FlamMap, the US Forest Service tool, to show how close our results are.
• No step back: once these scores exist, a change to the model only ships if it does not make them worse.

We will update this page as each benchmark is published.

What it leaves out

Real fires can be faster and bigger than the simulation. It does not model:

• Embers. Wind can carry burning embers far ahead of a fire and start new spot fires. This is how many homes burn. The kit stops a fire at roads, water and town blocks that a real fire can jump.
• Homes as fuel. LANDFIRE maps most built-up areas as land that does not burn, so the fire stops at the edge of town. Real fires can spread from house to house.
• Changing weather. The wind and fuel dryness stay the same for the whole run. Real fires change with the time of day, wind shifts and fronts.
• Firefighting. Crews, aircraft and fire lines are not modelled.
• Fire making its own weather. Very large fires can create their own winds.

How to read a result

• Compare, don't predict. Use it to compare scenarios: which ignition is worse, how much a drier day matters, which slopes and canyons carry fire fastest.
• Look at the confidence line. Trust a result more when the card says the fuel data covers the area with high confidence.
• Treat times as a guide. "Burns by hour 6" means "under these steady conditions". Strong wind and dry fuel make real fires faster.
• Think about embers near homes. Where the fire reaches the edge of a neighbourhood, assume embers could carry it further.

Learn more

• Fire - Wildfire Spread Simulation: how to use the kit.