Which weather data are essential to calculate KBDI (Keetch-Byram Drought Index)?

By using daily precipitation (mm) and daily maximum temperature (C), KBDI has the potential to describe moisture deficiency in upper soil layer (Keetch and Byram 1968). KBDI that use minimum number of meteorological parameters (precipitation, maximum temperature), was originally developed for the southeastern forest of the United States and has been extensively used for fire potential assessment in the U.S. (Keetch and Byram 1968). This index, which conceptually describes the soil moisture (Dolling et al. 2005) with several simple criteria, is based on the amount of daily precipitation, daily maximum temperature and mean annual precipitation (KBDI Drought paper).

The Keetch-Byram drought index (KBDI) is a continuous reference scale for estimating the dryness of the soil and duff layers. The index increases for each day without rain (the amount of increase depends on the daily high temperature) and decreases when it rains. The scale ranges from 0 (no moisture deficit) to 800. The range of the index is determined by assuming that there is 8 inches of moisture in a saturated soil that is readily available to the vegetation.

The Keetch-Byram Drought Index (KBDI) uses a mathematical function to correlate weather conditions to potential fire danger, which can be applied both to accidental and deliberate fire initiation. The index is a number that represents the net effect of evapotranspiration and precipitation, which might lead to a soil moisture deficit in the duff and upper soil layers. Actually, it is a hydrological approach of fire danger and its application is only limited to forests. It is based upon a rather simple representation of a forest where the forest vegetation density is controlled by the mean annual rainfall, which controls the rate of soil moisture loss. The loss rate will decrease with lower forest vegetation density, hence with lower annual rainfall. The KBDI is based on 8 in.(203mm) of soil water available for evapotranspiration (Keetch and Byram, 1968). It is expressed in hundredths of an inch on a scale from 0 to 800*0.01 in.)

The KBDI has been widely used for assessing fire danger because it is easy to calculate (Dimitrakopoulos and Bemmerzouk, 2003) and it does not require a lot of data (i.e. daily maximum air temperature and rainfall at a nearby standard meteorological station). Several studies have applied the KBDI in other areas than Florida State, such as Northern Eurasia (Groisman et al., 2007), Hawaii (Dolling et al., 2005), Australia (Boer et al., 2009; Finkele et al., 2006), Russia (Malevsky-Malevich et al., 2008), Mediterranean regions (Petros et al., 2011), in Southeast Asia, such as Indonesia (Murdiyarso et al., 2002) and Malaysia (Ainuddin and Ampun, 2008). Heim (2002) and Petros et al. (2011) indicate that the KBDI is the most widely used and accepted index for forest fire monitoring and prediction.

The Keetch-Byram drought index (KBDI) was developed for use by fire control managers and has become the most worldwide used index in wildfire monitoring and prediction, mainly due to its easy implementation compared to other indices which normally needmoremeteorological data and complicated calculations (Heim, 2002; Ganatsas et al., 2011). Many efforts can be found in the literature on assessing the behavior of KBDI in different regions and climates, and modified versions adapted to local meteorological conditions have been widely proposed. Dolling et al. (2005) analyzed the natural variability of the index in the Hawaiian Islands conditions, paying especial attention to El Nino conditions.

Keetch J J, Byram O M (1968) A drought index for forest fire control. USDA For Serv Southeastern For and Range Exp Stn Res Pap SE-38

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