cffdrs (version 1.8.6)

fwiRaster: Raster-based Fire Weather Index System

Description

fwiRaster is used to calculate the outputs of the Canadian Forest Fire Weather Index (FWI) System for one day 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 takes rasterized input and generates raster maps as outputs.

Usage

fwiRaster(input,init=c(ffmc=85,dmc=6,dc=15),mon=7,out= "all",lat.adjust=TRUE,
  uppercase=TRUE)

Arguments

input

A stack or brick containing rasterized 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 inputs are entered is not important.

lat	(recommended)	Latitude (decimal degree, default=55)
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 vector that contains the initial values for FFMC, DMC, and DC or a stack that contains raster maps of the three moisture codes calculated for the previous day, which will be used for the current day's calculation. Defaults are the standard initial values for FFMC, DMC, and DC defined as the following:

ffmc	Fine Fuel Moisture Code (FFMC; unitless) of the previous day. Default value is 85.
dmc	Duff Moisture Code (DMC; unitless) of the previous day. Default value is 6.
dc	Drought Code (DC; unitless) of the previous day. Default value is 15.
lat	Latitude of the weather station (optional, default=55). Latitude values are used to make
	day length adjustments in the function.

mon

Month of the year (integer 1~12, default=7). Month is used in latitude adjustment (lat.adjust), it is therefore recommended when lat.adjust=TRUE was chosen.

out

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

lat.adjust

The function offers options for whether latitude adjustments to day lengths 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

By default, fwi returns a raster stack which includes both the input and the FWI System variables, as describe below:

Inputs

Including temp, rh, ws, and prec with lat 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

Details

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, the Duff Moisture Code, and the Drought Code) 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 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), fuel consumption (the Build-up Index) and fire intensity per unit length of fire front (the Fire Weather Index). 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 (http://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.

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. http://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). http://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. http://cfs.nrcan.gc.ca/pubwarehouse/pdfs/29152.pdf

See Also

fbp, fbpRaster, fwi, hffmc, hffmcRaster

Examples

# NOT RUN {
library(cffdrs)
require(raster)
# The test data is a stack with four input variables including 
# daily noon temp, rh, ws, and prec (we recommend tif format):
day01src <- system.file("extdata","test_rast_day01.tif",package="cffdrs")
day01 <- stack(day01src)
day01 <- crop(day01,c(250,255,47,51))
# assign variable names:
names(day01)<-c("temp","rh","ws","prec")
# (1) use the initial values
foo<-fwiRaster(day01)
plot(foo)
### Additional, longer running examples are commented out below ###
# (2) use initial values with larger raster
# day01 <- stack(day01src)
# names(day01)<-c("temp","rh","ws","prec")
# foo<-fwiRaster(day01)
# plot(foo)
# (3) Calculate FWI System variables based on the previous day's
# fwi output:
# load the second day inputs:
# day02src <- system.file("extdata","test_rast_day02.tif",package="cffdrs")
# day02 <- stack(day02src)
# names(day02)<-c("temp","rh","ws","prec")
# use the previous day's output as initial:
# foo1<-fwiRaster(day02,init=foo)
# plot(foo1)
# }