Fire Weather Index
Fire Weather Index System · Also known as: FWI, Canadian Fire Weather Index
The Fire Weather Index (FWI) System, developed by the Canadian Forest Service, is a comprehensive weather-based fire danger rating system consisting of six component indices and an overall Fire Weather Index. It uses daily weather observations (temperature, relative humidity, wind speed, and precipitation) to estimate fine-fuel moisture, fire behavior, and risk. The FWI System is used operationally across Canada, many U.S. states, and internationally for fire management decisions and fire danger forecasting.
Read the full method
Sign in with a free account to read this section.
Method map
The neighbourhood of related methods — select a node to explore.
When to use it
Use the FWI System operationally for fire danger watches and warnings, fire incident response prioritization, and pre-fire planning. It is particularly effective for boreal and temperate forest fire management. The FWI System integrates weather-based and fuel-based fire danger components, making it more comprehensive than weather indices alone. Widely adopted in Canada, northern U.S., and internationally.
Strengths & limitations
- Comprehensive multi-timescale system capturing immediate (1-hour), short-term (10-hour), and long-term (100+ hour) fuel drying
- Based on fundamental fire dynamics principles and validated against observed fire behavior and occurrence
- Requires only standard weather data (temperature, humidity, wind, rain) available from networks worldwide
- Operational standard in Canada and increasingly adopted internationally for consistency
- Strong empirical performance: FWI correlates well with fire occurrence, spread, and burn area across diverse forest types
- Enables international comparison of fire danger using the same indices
- Originally developed for boreal forests; applicability to tropical, arid, or grassland fire systems may require recalibration
- Does not account for vegetation type variation; assumes a standard boreal forest fuel complex
- Carry-over calculations require continuous daily weather data; gaps or missing data compromise the system
- Topographic effects (elevation, aspect, shading) are not represented; FWI is point-based
- Live fuel moisture (foliage of shrubs and trees) is not directly modeled; only dead fuel moisture is estimated
Frequently asked
What is the difference between FFMC, DMC, DC, ISI, BUI, and FWI?
FFMC (Fine Fuel Moisture Code) represents 1-hour fuel moisture and updates daily with weather. DMC (Duff Moisture Code) represents 10-hour fuel moisture and responds on a week timescale. DC (Drought Code) represents 100+ hour fuel moisture (very deep drying) and responds over months. ISI (Initial Spread Index) estimates how fast a surface fire spreads given weather. BUI (Buildup Index) estimates total fuel available. FWI combines ISI and BUI into a single fire danger score (0–100+).
How do I calculate FWI if I have weather data?
Use the published FWI equations (Van Wagner 1989) or free software implementations (Canadian Forest Service provides Fortran code, and many open-source implementations in Python and R exist). Input your daily weather at noon local time and the previous day's FFMC, DMC, DC values. Calculate the new FFMC, DMC, DC, then ISI, BUI, then FWI.
Can I use FWI in tropical regions?
The FWI System was developed for boreal forests and may not perform well in tropical rainforests where moisture is high and fire is rare. However, in tropical dry forests or savannas with pronounced dry seasons, FWI may provide useful guidance. Validation against local fire observations is essential.
What do I do if I have missing weather data?
Missing daily weather data breaks the carryover chain in FWI calculations, compromising subsequent values. Options: interpolate the missing weather from nearby stations or spatially gridded data, or restart the system with a neutral initial condition once you have data again. Avoid using long gaps (> 5–10 days) without data.
Sources
- Van Wagner, C. E. (1987). Development and structure of the Canadian Forest Fire Weather Index System. Canadian Forestry Service Publication 1333. link ↗
- Van Wagner, C. E., & Pickett, T. L. (1989). Equations and FORTRAN program for the Canadian Forest Fire Weather Index System. Canadian Forestry Service Research Notes No. 5. link ↗
How to cite this page
ScholarGate. (2026, June 3). Fire Weather Index System. ScholarGate. https://scholargate.app/en/forestry/fire-weather-index
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Keetch-Byram Drought IndexForestry↔ compare
- Rothermel Fire ModelForestry↔ compare