R/ROStcalc.r

In cffdrs: Canadian Forest Fire Danger Rating System

.ROStcalc <- function(FUELTYPE, ROSeq, HR, CFB){
  #############################################################################
  # Description:
  #   Computes the Rate of Spread prediction based on fuel type and FWI
  #   conditions at elapsed time since ignition. Equations are from listed 
  #   FCFDG (1992).
  #
  #   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.
  #
  # Args:
  #   FUELTYPE: The Fire Behaviour Prediction FuelType
  #      ROSeq: Equilibrium Rate of Spread (m/min)
  #         HR: Time since ignition (hours)
  #        CFB: Crown Fraction Burned
  # Returns:
  #   ROSt: Rate of Spread at time since ignition
  #
  #############################################################################
  #Eq. 72 - alpha constant value, dependent on fuel type
  alpha <- ifelse(FUELTYPE %in% c("C1", "O1A", "O1B", "S1", "S2", "S3", "D1"),
                    0.115,
                    0.115 - 18.8 * (CFB**2.5) * exp(-8* CFB))
  #Eq. 70 - Rate of Spread at time since ignition
  ROSt <- ROSeq * (1 - exp(-alpha * HR))
  return(ROSt)
}