Keetch–Byram drought index

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The Keetch–Byram drought index (KBDI), created by John Keetch and George Byram in 1968 for the United States Department of Agriculture's Forest Service, is a measure of drought conditions. It is commonly used for the purpose of predicting the likelihood and severity of wildfire. It is calculated based on rainfall, air temperature, and other meteorological factors[1].

The KBDI is an estimate of the soil moisture deficit, which is the amount of water necessary to bring the soil moisture to its full capacity. A high soil moisture deficit means there is little water available for evaporation or plant transpiration[2]. This occurs in conditions of extended drought, and has significant effects on fire behaviour.

In the United States, it is expressed as a range from 0 to 800, referring to hundredths of an inch of deficit in water availability; in countries that use the metric system, it is expressed from 0 to 200, referring to millimetres[3].

Index value (hundredths of inches) Index value (millimetres) Implications[4][5]
0–200 0–50 Soil is moist. 0 represents a completely saturated soil[6].
200–400 50–100 Leaf litter begins to dry.
400–600 100–150 Lower litter actively contributes to fire intensity and will burn actively.
600–800 150–200 Associated with severe drought and extreme fire behaviour.

See alsoEdit


  1. ^ Keetch, John J.; Byram, George M. "A Drought Index for Forest Fire Control". USDA Forest Service Southern Research Station. Retrieved August 11, 2016. (Date: 1968) Res. Paper SE-38. 32 pp. Asheville, NC: U.S. Department of Agriculture, Forest ServiceCS1 maint: uses authors parameter (link)
  2. ^ Finkele, Klara; Mills, Graham A. (September 2006). "National gridded drought factors and comparison of two soil moisture deficit formulations used in prediction of Forest Fire Danger Index in Australia". Australian Meteorological Magazine. 55 (3): 183–197.
  3. ^ "Weather and Bushfire Behaviour" (PDF). NSW Rural Fire Service. Retrieved 20 March 2018.
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