R/fire_weather_index.r

In nrcan-cfs-fire/cffdrs: Canadian Forest Fire Danger Rating System

#' Fire Weather Index Calculation.
#'
#' @description 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.
#'
#'
#' @param isi  Initial Spread Index
#' @param bui Buildup Index
#'
#' @return A single fwi value
#'
#' @noRd

fire_weather_index <- function(isi, bui) {
  # Eqs. 28b, 28a, 29
  bb <- ifelse(
    bui > 80,
    0.1 * isi * (1000 / (25 + 108.64 / exp(0.023 * bui))),
    0.1 * isi * (0.626 * (bui^0.809) + 2)
  )
  # Eqs. 30b, 30a
  fwi <- ifelse(bb <= 1, bb, exp(2.72 * ((0.434 * log(bb))^0.647)))
  return(fwi)
}

.fwiCalc <- function(...) {
  .Deprecated("fire_weather_index")
  return(fire_weather_index(...))
}