R/LBcalc.r

In cffdrs: Canadian Forest Fire Danger Rating System

.LBcalc <- function(FUELTYPE, WSV) {
  #############################################################################
  # Description:
  #   Computes the Length to Breadth ratio of an elliptically shaped fire. 
  #   Equations are from listed FCFDG (1992) except for errata 80 from 
  #   Wotton et. al. (2009).
  #
  #   All variables names are laid out in the same manner as Forestry Canada 
  #   Fire Danger Group (FCFDG) (1992). Development and Structure of the 
  #   Canadian Forest Fire Behavior Prediction System." Technical Report 
  #   ST-X-3, Forestry Canada, Ottawa, Ontario.
  #
  #   Wotton, B.M., Alexander, M.E., Taylor, S.W. 2009. Updates and revisions to
  #   the 1992 Canadian forest fire behavior prediction system. Nat. Resour. 
  #   Can., Can. For. Serv., Great Lakes For. Cent., Sault Ste. Marie, Ontario, 
  #   Canada. Information Report GLC-X-10, 45p.
  #
  # Args:
  #   FUELTYPE: The Fire Behaviour Prediction FuelType
  #        WSV: The Wind Speed (km/h)
  # Returns:
  #   LB: Length to Breadth ratio
  #
  #############################################################################
  #calculation is depending on if fuel type is grass (O1) or other fueltype
  LB <- ifelse(FUELTYPE %in% c("O1A", "O1B"),
          #Correction to orginal Equation 80 is made here
          #Eq. 80a / 80b from Wotton 2009
          ifelse(WSV >= 1.0, 1.1 * (WSV**0.464), 1.0), #Eq. 80/81
          1.0 + 8.729 * (1-exp(-0.030 * WSV))**(2.155)) #Eq. 79
  return(LB)
}