waf {firebehavioR}

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

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.

Value

a vector of wind adjustment factors

Author(s)

Justin P Ziegler, [e-mail]

References

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

Examples

#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)