| fwiRaster {cffdrs} | R Documentation |
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.
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 (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
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.
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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:
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mon |
Month of the year (integer 1~12, default=7). Month is used in
latitude adjustment ( | ||||||||||||||||
out |
The function offers two output options, | ||||||||||||||||
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 |
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, fbpRaster, fwi,
hffmc, hffmcRaster
Examples
library(cffdrs)
require(terra)
# The test data is a stack with four input variables including
# daily noon temp, rh, ws, and prec (we recommend tif format):
day01src <- rast(
system.file("extdata", "test_rast_day01.tif", package = "cffdrs")
)
day01 <- crop(day01src, 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 ###
# (2) use initial values with larger raster
day01 <- day01src
names(day01) <- c("temp", "rh", "ws", "prec")
foo <- fwiRaster(day01)
plot(foo)