The Keetch–Byram drought index (known as 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 calculated based on rainfall, air temperature, and other meteorological factors.
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.