Wildfire Risk Calculator
Calculate wildfire risk level based on humidity, wind speed, drought duration, vegetation type, and temperature.
Get a Low to Extreme risk rating.
Wildfire risk depends on the interaction of several environmental factors. No single factor determines fire danger — it is their combination that matters.
Relative Humidity is one of the most important factors. Dry vegetation (low humidity) ignites far more easily than moist vegetation. Humidity below 20% is considered critical fire weather. Below 10% is extreme. Above 50% significantly reduces fire danger.
Wind Speed spreads fire and dries out vegetation rapidly. Higher wind speeds increase fire spread rate exponentially. Winds above 25 mph (40 km/h) are considered critical for fire spread. Gusty or erratic winds are especially dangerous.
Days Without Rain (Drought Duration) reflects how dry the soil and vegetation are. After 7–10 days without rain, surface fuels dry significantly. After 21+ days, deep fuels (roots, large logs) also become dangerously dry.
Vegetation Type affects ignition risk and fire intensity:
- Dry grass ignites instantly but burns out quickly.
- Shrubs burn hotter and longer than grass.
- Dense forest has enormous fuel loads and can produce catastrophic crown fires.
Temperature raises fire risk directly — heat dries fuels and the atmosphere, lowering relative humidity. High temperatures combined with low humidity and wind create the most dangerous fire weather conditions.
This calculator uses a simplified scoring system inspired by the Fosberg Fire Weather Index (FFWI) and the National Fire Danger Rating System (NFDRS). The FFWI was developed by Richard Fosberg in 1978 and combines wind speed, humidity, and temperature into a single fire danger number. This tool provides a general estimate — always consult local fire authority alerts for official conditions.
Risk levels:
- Low (0–19): Fuels do not ignite easily. Fires will burn slowly with low intensity.
- Moderate (20–39): Fires start easily and spread at moderate rates.
- High (40–59): Fires start very easily and spread rapidly. Control is difficult.
- Very High (60–79): Fires start extremely easily, burn intensely, and spread very rapidly.
- Extreme (80–100): Any fire that starts will likely be uncontrollable. Evacuate if ordered.