Wildfire field guide
Fire Intensity vs Burn Severity: what is the difference?
Intensity describes energy release while a fire is burning. Severity describes the degree of change or damage left behind. They are related, but one cannot be substituted for the other.
Core distinction
Behavior during the fire vs effects after the fire.
USGS and NWCG separate fire intensity from fire or burn severity. Intensity concerns energy output; severity concerns how much a site, soil or organic material was altered by the fire.
Describes energy release during combustion. Fireline intensity, reaction intensity, flame length and radiant energy are different ways to characterize aspects of that output.
Describes fire effects such as soil heating, duff and litter consumption, organic-matter loss and other changes at the site.
Why confusion matters
A high-intensity flame front does not uniquely determine severity.
Severity depends not only on how intense combustion is, but also on how long heat acts on a location, the fuels involved, moisture, soil and other site conditions. NWCG describes fire severity loosely as a product of intensity and residence time.
Remote sensing
Burn severity maps are post-fire evidence.
Satellite-derived severity products are generally used to assess changes after fire by comparing pre- and post-fire conditions. They should not be presented as direct measurements of flame intensity at every location.
- Intensity is a fire-behavior concept.
- Severity is an effects concept.
- Remote-sensing severity classes are derived indicators, not direct thermometers of the flame front.
- Ecosystem recovery is a later response and is not identical to severity itself.
Sources
USGS and NWCG terminology.
USGS — Fire intensity, fire severity and burn severity ↗
Published 21 September 2026.