KBDI as an Indicator of
Potential Wildfire Activity

The Keetch-Byram Drought Index (KBDI) is used by the Florida Division of Forestry to indicate the dryness of the soil and surface fuels. High values of the drought index are associated with severe wildfire outbreaks such as occurred during 1998. However, no threshold point has previously been determined to indicate that conditions are far above normal and warrant concern. Using 35 years of rainfall and temperature measurements from 9 locations throughout the state average KBDI values are determined for the state on a regional basis. These regions are North (stations used are Pensacola, Tallahassee and Jacksonville), Central (Daytona, Gainesville and Orlando) and South (Tampa, Fort Myers and Miami). This work operates under the premise that wide spread drought is accompanied by severe wildfire outbreaks. The average KBDI is compared to recent levels of fire activity (1981-present) to determine threshold levels that indicate above normal fire activity.

The mean drought conditions show a wide range of variability by region (Figure 1). Winter conditions are driest in the south and become wetter to the north as the central and northern regions experience a greater frequency of frontal passages. During the summer, convective activity produces significant rainfall particularly in the southern part of the state. Florida's fire season is clearly event in Figure 1 with the increased activity beginning in January and peaking in May and June. All three regions exhibit a peak in their KBDI around May-June period. Drought conditions are high during the fall but fire activity is at a minimum. This shows the need for any threshold values to be determined on a monthly basis to account for the seasonal variation in fire activity.

Figure 1. Mean regional KBDI along with mean number of acres burned statewide

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