R/buiCalc.R

In cffdrs: Canadian Forest Fire Danger Rating System

.buiCalc <- function(dmc, dc) {
  #############################################################################
  # Description: Buildup Index Calculation. All code
  #              is based on a C code library that was written by Canadian
  #              Forest Service Employees, which was originally based on
  #              the Fortran code listed in the reference below. All equations
  #              in this code refer to that document.
  #
  #              Equations and FORTRAN program for the Canadian Forest Fire 
  #              Weather Index System. 1985. Van Wagner, C.E.; Pickett, T.L. 
  #              Canadian Forestry Service, Petawawa National Forestry 
  #              Institute, Chalk River, Ontario. Forestry Technical Report 33. 
  #              18 p.
  #
  #              Additional reference on FWI system
  #
  #              Development and structure of the Canadian Forest Fire Weather 
  #              Index System. 1987. Van Wagner, C.E. Canadian Forestry Service,
  #              Headquarters, Ottawa. Forestry Technical Report 35. 35 p.
  #  
  #
  # Args:   dc:   Drought Code
  #        dmc:   Duff Moisture Code
  #
  # Returns: A single bui value
  #
  #############################################################################
  #Eq. 27a
  bui1 <- ifelse(dmc == 0 & dc == 0, 0, 0.8 * dc * dmc/(dmc + 0.4 * dc))
  #Eq. 27b - next 3 lines
  p <- ifelse(dmc == 0, 0, (dmc - bui1)/dmc)
  cc <- 0.92 + ((0.0114 * dmc)^1.7)
  bui0 <- dmc - cc * p
  #Constraints
  bui0 <- ifelse(bui0 < 0, 0, bui0)
  bui1 <- ifelse(bui1 < dmc, bui0, bui1)
  return(bui1)
}