waf: Calculated wind adjustment factor
In zieg9479/firebehavioR: Prediction of Wildland Fire Behavior and Hazard

Description Usage Arguments Details Value Author(s) References Examples

Prediction of wind adjustment factor for sheltered and unsheltered fuels.

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

`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

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.

a vector of wind adjustment factors

Justin P Ziegler, justin.ziegler@colostate.edu

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.

#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)