The Severe Fire Danger Index (SFDI) is a categorical rating designed to flag conditions associated with extreme fire activity. It combines the Energy Release Component (ERC) and Burning Index (BI), expressed as percentiles, into a single metric. Those percentiles are normalized against a long-term climatology and sorted into five classes: Low, Moderate, High, Very High, and Severe. The class breakpoints fall at the 60th, 80th, 90th, and 97th percentiles, matching the thresholds US fire agencies use to set adjective fire danger ratings, staffing levels, and resource prepositioning.
Because it is normalized against local climatology, a given SFDI class carries the same meaning across different regions and seasons. The index can be forecast from short-term weather predictions, which lets it provide early warning of dangerous conditions before they arrive.