Fire Severity Index (FSI) – Understanding Wildfire Conditions in the UK

What Is the Fire Severity Index?

The Fire Severity Index (FSI) evaluates how severe a wildfire could become if one were to ignite under current weather conditions. Developed to support Natural England, Natural Resources Wales (formerly the Countryside Council for Wales) and other Relevant Authorities undertake their statutory duties under the CROW Act 2000, the FSI provides an objective way to show when exceptional conditions occur. Relevant Authorities must, under the CROW Act, make reasonable efforts to identify exceptional conditions and suspend open access rights on vulnerable land as necessary.

It’s important to note that the FSI does not predict when or where wildfires will start. Instead, it analyses up-to-date weather data—such as rainfall, drought, wind speed, temperature, and humidity—to determine how these factors could affect fire behaviour. Humidity is especially significant in the UK, as dry conditions can cause dead vegetation to become more flammable and increase fire severity.

How Is the FSI Used?

The Met Office updates the FSI every day, providing the latest information to Natural England which they then display on their Open Access website. The information is used by the Relevant Authorities to suspend open access rights by triggering any fire prevention exclusions when conditions are exceptional.  

Our expert meteorologists use the FSI data to create an assessment of wildfire risk for the UK within the Natural Hazard Partnership (NHP) daily hazard assessment used by the responder community to enhance public safety.

Met Office support for wildfire awareness and response

While the Met Office does not offer a dedicated wildfire service, we provide reliable information to support UK wildfire awareness and safety.

• A UK-wide assessment of wildfire conditions for the responder community within the Daily Hazard Assessment as part of the Natural Hazard Partnership 
• Weather Forecasts and Warnings: Our meteorologists issue regular weather updates and warnings for the UK—several times daily—helping the public, land managers and responders prepare for changing conditions that could impact wildfire risk.
• Longer-Term Outlooks: Upon request, we provide tailored extended forecasts working with the National Hazard Partnership to support Government on the long-term wildfire conditions across the UK.
• During an incident we also support responders with FireMet and CHEMET.