Enter the degree of curing, temperature, relative humidity, and wind speed into the calculator to estimate the Grassland Fire Danger Index (GFDI). Use the Forest (FFDI) tab to calculate the Forest Fire Danger Index using drought factor instead.
Grassland Fire Danger Index Formula
The following formula is commonly used to calculate the McArthur Grassland Fire Danger Index (GFDI).
GFDI = exp( -23.6 + 5.01 * ln(C) + 0.0281 * T - 0.226 * sqrt(RH) + 0.633 * sqrt(U) )
- GFDI is the Grassland Fire Danger Index
- C is the degree of curing of grass fuels (%) (0–100)
- T is the air temperature in degrees Celsius (°C)
- RH is the relative humidity (%)
- U is the wind speed at 10 m in km/h
- ln(.) is the natural logarithm and exp(.) is the natural exponential (ex)
To calculate GFDI, take the natural log of the degree of curing and multiply by 5.01. Add 0.0281 times temperature. Subtract 0.226 times the square root of relative humidity. Add 0.633 times the square root of wind speed. Finally, take the exponential (exp) of the total. (If curing is 0%, the index is effectively 0.)
What is a Grassland Fire Danger Index?
The Grassland Fire Danger Index (GFDI) is a tool used to predict the risk and severity of grassland fires based on weather conditions and the curing (dryness) of grass fuels. It takes into account factors such as temperature, humidity, wind speed, and how cured the vegetation is to estimate the potential for a fire to start, spread, and become difficult to control. The index is typically used by fire agencies to manage resources and issue warnings to the public.
How to Calculate Grassland Fire Danger Index?
The following steps outline how to calculate the Grassland Fire Danger Index (GFDI) using the given formula:
- First, determine the degree of curing (C) as a percentage from 0–100.
- Next, determine the temperature in degrees Celsius (T).
- Next, determine the relative humidity (RH) as a percentage.
- Next, determine the wind speed at 10 m in km/h (U).
- Using the formula GFDI = exp( -23.6 + 5.01 * ln(C) + 0.0281 * T - 0.226 * sqrt(RH) + 0.633 * sqrt(U) ), substitute the values of C, T, RH, and U into the formula.
- Finally, calculate the Grassland Fire Danger Index (GFDI) using the substituted values.
Example Problem:
Use the following variables as an example problem to test your knowledge:
degree of curing (C) = 70%
temperature (T) = 25°C
relative humidity (RH) = 50%
wind speed (U) = 20 km/h
