North Carolina State Climate Office
The Keetch-Byram Drought Index (KBDI) assesses the likelihood of wildfires becoming large and difficult to contain by representing the net effect of evapotranspiration and precipitation in producing cumulative moisture deficiency in deep duff and upper soil layers.
The KBDI attempts to measure the amount of precipitation, in hundredths of inches, necessary to return the soil to full field capacity. The index ranges from zero, the point of no moisture deficiency, to 800, the maximum drought that is possible, and represents a moisture regime from 0 to 8 inches of water through the soil layer. At 8 inches of water, the KBDI assumes saturation. At any point along the scale, the index number indicates the amount of net rainfall that is required to reduce the index to zero, or saturation.
While KBDI does not indicate the risk of fire activity, at higher KBDI values, fires that do ignite are likely to be longer-lasting due to the increased dry fuel loading, and may require additional resources beyond local firefighting crews.
The KBDI from the Fire Weather Intelligence Portal, currently hosted by the North Carolina State Climate Office, is a gridded product based on National Weather Service radar-based precipitation estimates and gridded temperature estimates from PRISM and Real-Time Mesoscale Analysis.