firebehavioR (version 0.1.2)

waf: Calculated wind adjustment factor

Description

Prediction of wind adjustment factor for sheltered and unsheltered fuels.

Usage

waf(fuelDepth, forestHt, cr, cc, sheltered = "n")

Arguments

fuelDepth

a numeric vector of surface fuel bed depths (cm)

forestHt

a numeric vector of average stand tree heights (m)

cr

a numeric vector of crown ratios (%)

cc

a numeric vector of canopy cover (%)

sheltered

a character vector of either "y" or "n" (default) to use sheltered or not (unsheltered) equations

Value

a vector of wind adjustment factors

Details

This calculates the wind adjustment factor (ratio of 20-ft open wind speed to wind speed at midflame height of a surface fire). One of two equations are used, depending on user input: by default, this function assumes the surface fuel bed is unsheltered. fuelDepth must be a positive value if the unsheltered variant is invoked. There are two conditions to enable calculation for a sheltered fuelbed. One, the product of cr and cc must exceed 5%. Alternatively, if cr and cc are not supplied, the user may enter "sheltered = y". The former method is recommended when cr and cc are known. In addition, either means of invoking the sheltered equation must also have forestHt provided.

References

Andrews, P.L. 2012. Modeling wind adjustment factor and midflame wind speed for Rothermel<U+2019>s surface fire spread model. RMRS-GTR-266. USDA Forest Service Rocky Mountain Research Station.

Examples

# NOT RUN {
#Sheltered fuelbed with a 10 m tall forest with unknown crown ratio and canopy cover
waf(forestHt = 10, sheltered = 'y')
#Sheltered fuelbed with known high crown ratio and canopy cover
waf(forestHt = 10, cr = 40, cc = 40)
#Sheltered fuelbed with known low crown ratio and canopy cover
waf(fuelDepth = 1, forestHt = 10, cr = 10, cc = 10)
#Because cr and cc are low, the previous solution is equivalent to an unsheltered fuelbed
waf(fuelDepth = 1)
# }