What is the KBDI?
The wildfire activity potential forecast is based on the Keetch-Byram Drought Index (KBDI). The Florida Division of Forestry offers excellent primers on KBDI-based Drought classification as well as its use as an indicator of potential wildfire activity. Because of the chaotic nature of weather, all climate forecasts (including this wildfire threat forecast) are presented in terms of probabilities.
Weather data that drives the forecast are taken from hundreds of National Weather Service (NWS) cooperative observer sites in Florida, Georgia and Alabama. The large number of weather stations makes it possible to provide the forecast at a county level.
It has been shown that increased wildfire activity is linked with the deviation of the KBDI from seasonal normals. The KBDI tends to be at its peak in May, so values around 400 or 500 are not unusual at this time and do not indicate an increased threat. The substantial threat instead comes when KBDI values are 1 to 1.5 (or more) standard deviations (from these seasonal normals) above the seasonal average.
The wildfire threat forecast is presented in a series of color-coded maps showing the probability of the KBDI being in the following threat categories.
- Abnormally dry (450 or above)
- Moderately dry (500 or above)
- Severely dry (550 or above)
- Extremely dry (650 or above)
Since the KBDI is driven by daily weather and can change drastically based on one or more rainfall events, the maps show the probability of exceeding the threat level at least 7 days during the month, rather than for the month as a whole.
The forecast is based on both initial conditions (current KBDI values) and expected climate patterns associated with ocean temperatures in the tropical Pacific. For this reason, the forecast will be updated monthly throughout the season as conditions change in the field. Note that no forecasts are given for North Alabama and North Georgia due to a lack of skill (no discernable climate signal) in these regions.