The Cumulative Severity Index (CSI) or Keetch-Byram Drought Index (KBDI) is a continuous reference scale for estimating the dryness of the soil and duff layers. This system is based primarily on recent rainfall patterns.
The KBDI, specifically developed to equate the effects of drought with potential fire activities, is the most widely used system by fire managers in the southeastern United States. This mathematical system for relating current and recent weather conditions to potential or expected fire behavior results in a drought index number ranging from 0 to 800. This number accurately describes the amount of moisture that is missing; a rating of 0 defines a point of no moisture deficiency and 800 defines the maximum drought possible.
Prolonged droughts (high KBDI) influence fire intensity since more fuel is available for combustion (i.e. fuels have a lower moisture content). In addition, dry organic material in the soil can lead to increased difficulty in fire suppression. High values of the KBDI are an indication that conditions are favorable for the occurrence and spread of wildfires, but drought is not by itself a prerequisite for wildfires. Other weather factors, such as wind, temperature, relative humidity and atmospheric stability, play a major role in determining the actual fire danger.
These KBDI numbers correlate with potential fire behavior:
0 - 200 Soil and fuel have a high moisture content. Most fuels will not readily ignite or burn. However, with sufficient sunlight and wind, cured grasses and some light surface fuels will burn in spots and patches.
200 - 400 Fuels more readily burn, and fire can move across an area with no “gaps.” Heavier fuels do not readily ignite and burn. Smoldering and the resulting smoke to carry into and possibly through the night.
400 - 600 Fire intensity significantly increases. Fire readily burns in all directions exposing mineral soils in some locations. Larger fuels may burn or smolder for several days creating possible smoke and control problems.
600 - 800 Fire burns to mineral soil. Stumps will burn to the end of underground roots and spotting will be a major problem. Fires will burn through the night and heavier fuels will actively burn and contribute to fire intensity.
Last modified: Thursday, 27-Dec-2012 15:27:13 EST