About the Angström Index

The Angström Index is a widely used European fire weather index. Lower values indicate higher fire risk. A value below 2.5 indicates elevated fire danger; below 1.0 is considered extreme. The index is calculated daily from the maximum temperature and the minimum relative humidity recorded at the station.

Formula: A = (RH_min / 20) + (27 − T_max) / 10

About the Fire Weather Index (FWI)

The Canadian Forest Fire Weather Index (FWI) system is the international standard used by fire services worldwide, including in the Netherlands (KNMI) and across Europe. It uses temperature, relative humidity, wind speed, and precipitation to calculate several sub-indices: the Fine Fuel Moisture Code (FFMC), the Duff Moisture Code (DMC), the Drought Code (DC), and the Initial Spread Index (ISI), which together form the final FWI. This station currently computes the simpler Angström Index from on-site data. A full FWI calculation requires wind data as well.