fwi {cffdrs}

Fire Weather Index System

Description

fwi is used to calculate the outputs of the Canadian Forest Fire Weather Index (FWI) System for one day or one fire season based on noon local standard time (LST) weather observations of temperature, relative humidity, wind speed, and 24-hour rainfall, as well as the previous day's fuel moisture conditions. This function could be used for either one weather station or for multiple weather stations.

The Canadian Forest Fire Weather Index (FWI) System is a major subsystem of the Canadian Forest Fire Danger Rating System, which also includes Canadian Forest Fire Behavior Prediction (FBP) System. The modern FWI System was first issued in 1970 and is the result of work by numerous researchers from across Canada. It evolved from field research which began in the 1930's and regional fire hazard and fire danger tables developed from that early research.

The modern System (Van Wagner 1987) provides six output indices which represent fuel moisture and potential fire behavior in a standard pine forest fuel type. Inputs are a daily noon observation of fire weather, which consists of screen-level air temperature and relative humidity, 10 meter open wind speed and 24 accumulated precipitation.

The first three outputs of the system (the Fire Fuel Moisture Code (ffmc), the Duff Moisture Code (dmc), and the Drought Code (dc)) track moisture in different layers of the fuel making up the forest floor. Their calculation relies on the daily fire weather observation and also, importantly, the moisture code value from the previous day as they are in essence bookkeeping systems tracking the amount of moisture (water) in to and out of the layer. It is therefore important that when calculating FWI System outputs over an entire fire season, an uninterrupted daily weather stream is provided; one day is the assumed time step in the models and thus missing data must be filled in.

The next three outputs of the System are relative (unitless) indicators of aspects of fire behavior potential: spread rate (the Initial Spread Index, isi), fuel consumption (the Build-up Index, bui) and fire intensity per unit length of fire front (the Fire Weather Index, fwi). This final index, the fwi, is the component of the System used to establish the daily fire danger level for a region and communicated to the public. This final index can be transformed to the Daily Severity Rating (dsr) to provide a more reasonably-scaled estimate of fire control difficulty.

Both the Duff Moisture Code (dmc) and Drought Code (dc) are influenced by day length (see Van Wagner 1987). Day length adjustments for different ranges in latitude can be used (as described in Lawson and Armitage 2008 (https://cfs.nrcan.gc.ca/pubwarehouse/pdfs/29152.pdf)) and are included in this R function; latitude must be positive in the northern hemisphere and negative in the southern hemisphere.

The default initial (i.e., "start-up") fuel moisture code values (FFMC=85, DMC=6, DC=15) provide a reasonable set of conditions for most springtime conditions in Canada, the Northern U.S., and Alaska. They are not suitable for particularly dry winters and are presumably not appropriate for different parts of the world.

Usage

fwi(
  input,
  init = data.frame(ffmc = 85, dmc = 6, dc = 15, lat = 55),
  batch = TRUE,
  out = "all",
  lat.adjust = TRUE,
  uppercase = TRUE
)

Arguments

input

A dataframe containing input variables of daily weather observations taken at noon LST. Variable names have to be the same as in the following list, but they are case insensitive. The order in which the input variables are entered is not important.

id	(optional)	Unique identifier of a weather
		station or spatial point (no restriction on
		data type); required when batch=TRUE
lat	(recommended)	Latitude (decimal degree, default=55)
long	(optional)	Longitude (decimal degree)
yr	(optional)	Year of observation; required when batch=TRUE
mon	(recommended)	Month of the year (integer 1-12, default=7)
day	(optional)	Dayof the month (integer); required when batch=TRUE
temp	(required)	Temperature (centigrade)
rh	(required)	Relative humidity (%)
ws	(required)	10-m height wind speed (km/h)
prec	(required)	24-hour rainfall (mm)

init

A data.frame or vector contains either the initial values for FFMC, DMC, and DC or the same variables that were calculated for the previous day and will be used for the current day's calculation. The function also accepts a vector if the initial or previous day FWI values is for only one weather station (a warning message comes up if a single set of initial values is used for multiple weather stations). Defaults are the standard initial values for FFMC, DMC, and DC defined as the following:

Variable	Description	Default
ffmc	Previous day Fine Fuel Moisture Code (FFMC; unitless)	85
dmc	Previous day Duff Moisture Code (DMC; unitless)	6
dc	Previous Day Drought Code (DC; unitless)	15
lat	Latitude of the weather station (Optional)	55

batch

Whether the computation is iterative or single step, default is TRUE. When batch=TRUE, the function will calculate daily FWI System outputs for one weather station over a period of time chronologically with the initial conditions given (init) applied only to the first day of calculation. If multiple weather stations are processed, an additional "id" column is required in the input to label different stations, and the data needs to be sorted by date/time and "id". If batch=FALSE, the function calculates only one time step (1 day) base on either the initial start values or the previous day's FWI System variables, which should also be assigned to init argument.

out

The function offers two output options, out="all" will produce a data frame that includes both the input and the FWI System outputs; out="fwi" will generate a data frame with only the FWI system components.

lat.adjust

The function offers options for whether day length adjustments should be applied to the calculations. The default value is "TRUE".

uppercase

Output in upper cases or lower cases would be decided by this argument. Default is TRUE.

Value

fwi returns a dataframe which includes both the input and the FWI System variables as described below:

Input Variables

Including temp, rh, ws, and prec with id, long, lat, yr, mon, or day as optional.

ffmc

Fine Fuel Moisture Code

dmc

Duff Moisture Code

dc

Drought Code

isi

Initial Spread Index

bui

Buildup Index

fwi

Fire Weather Index

dsr

Daily Severity Rating

Author(s)

Xianli Wang, Alan Cantin, Marc-André Parisien, Mike Wotton, Kerry Anderson, and Mike Flannigan

References

1. Van Wagner, C.E. and T.L. Pickett. 1985. Equations and FORTRAN program for the Canadian Forest Fire Weather Index System. Can. For. Serv., Ottawa, Ont. For. Tech. Rep. 33. 18 p. https://cfs.nrcan.gc.ca/pubwarehouse/pdfs/19973.pdf

2. Van Wagner, C.E. 1987. Development and structure of the Canadian forest fire weather index system. Forest Technology Report 35. (Canadian Forestry Service: Ottawa). https://cfs.nrcan.gc.ca/pubwarehouse/pdfs/19927.pdf

3. Lawson, B.D. and O.B. Armitage. 2008. Weather guide for the Canadian Forest Fire Danger Rating System. Nat. Resour. Can., Can. For. Serv., North. For. Cent., Edmonton, AB. https://cfs.nrcan.gc.ca/pubwarehouse/pdfs/29152.pdf

See Also

fbp, fwiRaster, gfmc, hffmc, hffmcRaster, sdmc, overwinter_drought_code, fire_season

Examples

library(cffdrs)
# The test data is a standard test
# dataset for FWI system (Van Wagner and Pickett 1985)
data("test_fwi")
# Show the data, which is already sorted by time:
head(test_fwi)
# long  lat	yr	mon	day	temp	rh	ws	prec
# -100	40	1985	4	  13	17	  42	25	0
# -100	40	1985	4	  14	20	  21	25	2.4
# -100	40	1985	4	  15	8.5	  40	17	0
# -100	40	1985	4	  16	6.5	  25	6	0
# -100	40	1985	4	  17	13	  34	24	0

## (1) FWI System variables for a single weather station:
# Using the default initial values and batch argument,
# the function calculate FWI variables chronically:
fwi.out1 <- fwi(test_fwi)
# Using a different set of initial values:
fwi.out2 <- fwi(
  test_fwi,
  init = data.frame(ffmc = 80, dmc = 10, dc = 16, lat = 50)
)
# This could also be done as the following:
fwi.out2 <- fwi(test_fwi, init = data.frame(80, 10, 6, 50))
# Or:
fwi.out2 <- fwi(test_fwi, init = c(80, 10, 6, 50))
# Latitude could be ignored, and the default value (55) will
# be used:
fwi.out2 <- fwi(test_fwi, init = data.frame(80, 10, 6))

## (2) FWI for one or multiple stations in a single day:
# Change batch argument to FALSE, fwi calculates FWI
# components based on previous day's fwi outputs:

fwi.out3 <- fwi(test_fwi, init = fwi.out1, batch = FALSE)
# Using a suite of initials, assuming variables from fwi.out1
# are the initial values for different records.
init_suite <- fwi.out1[, c("FFMC", "DMC", "DC", "LAT")]
# Calculating FWI variables for one day but with multiple
# stations. Because the calculations is for one time step,
# batch=FALSE:
fwi.out4 <- fwi(test_fwi, init = init_suite, batch = FALSE)

## (3) FWI for multiple weather stations over a period of time:
# Assuming there are 4 weather stations in the test dataset, and they are
# ordered by day:
test_fwi$day <- rep(1:(nrow(test_fwi) / 4), each = 4)
test_fwi$id <- rep(1:4, length(unique(test_fwi$day)))
# Running the function with the same default initial inputs, will receive a
# warning message, but that is fine:
fwi(test_fwi)

## (4) Daylength adjustment:
# Change latitude values where the monthly daylength adjustments
# are different from the standard ones
test_fwi$lat <- 22
# With daylength adjustment
fwi(test_fwi)[1:3, ]
# Without daylength adjustment
fwi(test_fwi, lat.adjust = FALSE)[1:3, ]