Presets
Playback
Weather
Wind and fuel moisture.
Fuel and terrain
Fuel load, hill and what a click does.
Layers
Model checks
The science
Fire front as a travel-time problem
Wildland fire spread follows Huygens' principle: every burning point sends out a small elliptical wavelet and the envelope is the new front. On a grid this is a minimum-travel-time problem, solved here exactly with Dijkstra's algorithm on a 16-neighbour stencil. The rate of spread in direction θ from a cell is a product of factors in the spirit of Rothermel's model:
R(θ) = R0(fuel) · L · (1 − M/28) · exp(3.5 tanφ) · exp(3 k Umf cos(θ − θwind))R0 is the no-wind rate for grass, shrub or forest, M the fuel moisture (%), φ the local slope in the direction of travel, Umf = 0.6 U the mid-flame wind and k = 0.12 s/m. The ratio of upwind to downwind arrival times is then exp(2 · 3 k Umf), which the page checks. A cell burns for the chosen burn-out time and then turns to ash.
Honest simplifications
- Empirical factors, not Rothermel's full equations; spotting, crown fire, fire-generated winds and diurnal weather are not modelled.
- Wind is uniform in space and time; fuel is a coherent random patchwork rather than a mapped fuel model.
- Firebreaks and the river stop the fire completely, whereas embers can jump them in reality.
- This is a teaching model of fire physics, not an operational forecast.
What to try
- Start with Calm day: the burned area is a nearly circular patch whose area grows as t squared (third check).
- Raise the wind: the patch stretches downwind and the back rate collapses.
- Choose the click action draw firebreak, drag a line across the head of the fire and see the front wrap around it.
- Load Uphill run: the slope factor makes the fire climb the hill several times faster than it descends.