Keetch–Byram drought index

{{Short description|Estimate of soil moisture deficit}}

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 commonly used for the purpose of predicting the likelihood and severity of wildfires. It is calculated based on rainfall, air temperature, and other meteorological factors.{{cite journal |url=http://www.srs.fs.usda.gov/pubs/viewpub.jsp?index=40 |title=A Drought Index for Forest Fire Control |author1=Keetch, John J. |author2=Byram, George M. |journal=Res. Pap. Se-38. Asheville, Nc: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 35 P |year=1968 |volume=038 |publisher=USDA Forest Service Southern Research Station |access-date=August 11, 2016 |quote=(Date: 1968) Res. Paper SE-38. 32 pp. Asheville, NC: U.S. Department of Agriculture, Forest Service}}

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.{{cite journal|last1=Finkele|first1=Klara|last2=Mills|first2=Graham A.|title=National gridded drought factors and comparison of two soil moisture deficit formulations used in prediction of Forest Fire Danger Index in Australia|journal=Australian Meteorological Magazine|date=September 2006|volume=55|issue=3|pages=183–197}} 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.{{cite web|title=Weather and Bushfire Behaviour|url=https://www.rfs.nsw.gov.au/__data/assets/pdf_file/0020/23537/Bush-Fire-Bulletin-LIFTOUT-WeatherandBushFireBehaviour.pdf|publisher=NSW Rural Fire Service|accessdate=20 March 2018}}