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technical description of the fire module in iLand

fire module

fire module

The fire module is a sub module of iLand. See disturbance modules for a list of available modules.
For details on the modeling side of things, check the documentation for wildfire.

parameters

These fire-module specific parameters can be set in the project file below the modules.fire section. Some parameters of the fire module are global (i.e. valid for the whole landscape), others are stored on resource unit level (i.e., with a resolution of 1ha - see simulation extent for details how to prepare the data).

keydatatypedescriptiongrain
fire ignition
KBDIrefnumericreference value for the site specific KBDI (Keetch Byram Drought Index). See wildfire#fire_ignition. RU
meanAnnualPrecipitationnumericmean annual precipitation (mm).RU
rFireSuppressionnumericA scalar for fire suppression (rmgmt), see wildfire#fire_ignition. Default value: 1.RU
fireReturnIntervalnumericaverage number of years between two fires affecting a single pixel. A value of e.g. 100 means, that, on average, a pixel burns every 100 years.RU
fire spread
averageFireSizenumericaverage fire size in m2.RU
minFireSizenumericminimum fire size (m2). If minFireSize is set to a very high value, the fire size distribution has effectively no limiting effect on the simulated fire sizes.RU
maxFireSizenumericmaximum fire size (m2).RU
rLandnumericmultiplier for the fire spread probability for the resource unit (0..1). If below the (default) value of 1, fire spreads with a reduced probability (e.g. for riparian areas). See wildfire.RU
fireExtinctionProbabilitynumericprobability that a the fire on a burning pixel extincts without a chance to spread further. default: 0. RU
minimumFuelnumericthe minimum amount of fuel for a fire to burn on a cell (combustible fuel, yR (leafs and twigs) and yL (downed woody debris) in kg biomass/m2; default: 0.05global
fuel
fuelKFC1numericparameter kfC1 for calculation of fuel amount using compartment specific moisture relations (default: 0.8)global
fuelKFC2numericparameter kfC2 for calculation of fuel amount using compartment specific moisture relations (default: 0.2)global
fuelKFC3numericparameter kfC3 for calculation of fuel amount using compartment specific moisture relations (default: 0.4)global
wind
wind.speedMinnumericminimum wind speed (m/s)global
wind.speedMaxnumericmaximum wind speed (m/s). The wind speed is randomly selected between speedMin and speedMax for each fire event.global
wind.directionnumericthe main wind direction (in degrees). North=0, East=90, South=180, West=270. For each fire event the wind direction is calculated as direction +- 45°. global
mortality
onlySimulationbooleanonly if value is false real effects of fire (on trees, snags, soil pools) are simulated (default: false). A value of true can be useful for testing purposes.global
crownKill1numericparameter kCK1 to calculate fraction of crown kill. (default: 0.21111)global
crownKill1numericparameter kCK2 to calculate fraction of crown kill. (default: 0.00445)global
crownKillDbhnumericDbh-threshold (cm) dbh_thres used in crown kill calculations. (default: 40).
mortalityFormulastringFormula to calculate the provability of death for a single tree during a fire event. Variables are: bt: bark thickness (cm), ck: fraction of crown kill (0..1). (default: 1/(1 + exp(-1.466 + 1.91*bt - 0.1775*bt*bt - 5.41*ck*ck) ) ).global
burnSOMFractionnumericfraction (0..1) of SOM biomass that is assumed to be lost by a fire. 0=no biomass lost. (default: 0)global
burnStemFractionnumericfraction of stem biomass (0..1) of died trees that is combusted (default: 0.1)global
burnBranchFractionnumericfraction of branch biomass (0..1) of died trees that is combusted (default: 0.5)global
burnFoliageFractionnumericfraction of foliage biomass (0..1) of died trees that is combusted (default: 1.0)global
general
onAfterFirestringIf provided, the Javascript expression is called immediately after a fire event. The id of the fire can be accessed via the id propery of the Fire javascript object (see below). Default: ""global
allowBurnInbooleana value of 'true' is required for burn-ins (if true, iLand builds a map of edge pixels)


Fire specific visualization

The iLand GUI provides some means to visually inspect various fire-related variables during a iLand simulation. The visualization is based on resource units and (usually) cumulative, i.e. each fire event simply paints over the affected area.

  • fireID: numeric ID of each fire event
  • crownKill: crownKill-fraction (see wildfire ).
  • diedStemsFrac: fraction of killed trees on burning areas
  • diedBasalArea: basal area (sum over resource units) of burnt trees.
  • KBDI: Keetch Byram Drought Index (see wildfire ).
  • KBDIref: the reference KDBI used for calculations
  • baseIgnition: base probability of an annual fire ignition event for a cell on RU level (depending on fire-return-interval and average fire size)
  • fire spread: The spread of the last fire (this view is cleared for each new fire event)
  • fuel: burned fuel (forest floor + dwd) kg/ha
  • combustibleFuel: "available combustible fuel (current KBDI, forest floor + dwd) kg/ha
  • nFire: cumulative count of fire events on a resource unit
  • lastFireYear: simulation year of the last fire event on a RU


Fire specific JavaScript

The fire module sports a JavaScript binding allowing extended control on fire processes. When the fire module is active, the JavaScript engine contains a global variable Fire supporting the following functions and properties:

Properties

id
The numeric Id of the last fire event (integer, read-only). Each fire events has assigned an unique identifier that is also used in database outputs.

x
The (metric) x-coordinate of the ignition point of the last fire.

y
The (metric) y-coordinate of the ignition point of the last fire.

onIgnitionRU
If set to a valid Javascript function, then the function is called during the ignition phase for each resource unit. The function has the following signature:
mgmt_factor = Fire.onIgnitionRU(kbdi, mgmt_factor)
kbdi is the kbdi value on the resource unit, mgmt_factor the default factor for the RU. If a value is returned, it is used as the suppression factor (rMgmt) for the current RU, otherwise mgmt_factor is used.

// function is called for every RU
Fire.onIgnitionRU = function(kbdi, rmgmt) {
	// parameters: kbdi: the kbdi of the RU, 
	// rmgmt: the supression scalar (set in iLand)
	console.log("kbdi: " + kbdi + ", rmgmt: " + rmgmt);
	// calculate a new suppression factor based on the kbdi: (just a test)
	var r = rmgmt + 10*kbdi;
	// use this value for the current year on the RU:
	return r;
}


onCalculateFireSize
If set to a valid JavaScript function, then the function is called when the actual fire size is calcuated for a fire event. The function has the signature:
fire_size_m2 = onCalculateFireSize(rclim, fire_size)
with rclim the climate factor ($KBDI/KBDI_{ref}$), fire_size the value drawn from default distribution in iLand. The return value will be used as the fire size for the current event.

// helper function to get a random number between 'min' and 'max'
function runiform(min, max) {
  return Math.random() * (max - min) + min;
}

// calculate fire size; rclim=KBDI/KBDIRef, old_size=fire size drawn from standard distribution (iLand)
Fire.onCalculateFireSize = function(rclim, old_size) {
	if (rclim < 0.75) {
		return runiform(10000,200000);
	}
	if (rclim > 1.75)
		return runiform(2000000000, 450000000);
	
	// drawn from distribution, applied min/max range
	return old_size;
}


onIgnition
The handler is called immediately before the standard ignition routine is run and can be used to start prescribes fires.

Functions

Fire.ignite(x_meter, y_meter, firesize, windspeed, winddirection)
Ignite a fire event with pre-defined properties, i.e. at a given location (parameters x_meter, y_meter) with given conditions (i.e. wind direction and speed and fire size). if both x and y are set to -1, the ignition is performed stochastically, i.e. as used in dynamic simulation mode.
The return value is -1 if no fire was ignited, or the total burnt area (m2) otherwise.
x_meter, y_meter: metric coordinates of the ignition point in the landscape
firesize: provide a fire size (m2). The fire size will be drawn from the fire size distribution if firesize=-1 or omitted.
windspeed: wind speed (m/s), drawn randomly if omitted or -1.
winddirection: wind direction (0°=N..180°=S..270=W°), drawn randomly if omitted or set to -1.

// start a fire at 100/100
  Fire.ignite(100, 100);
  // start a fire with pre-defined fire size (1 ha)
  Fire.ignite(100, 100, 10000);


Fire.igniteBurnIn(x_meter, y_meter, perimeter_length, firesize_m2, simulate=false)
The function starts a fire not from a point, but from a line along the iLand landscape perimeter. The incoming fire front is defined by a center point along the perimeter (x_meter / y_meter in the iLand reference system, the model looks for the closest 20m edge pixel within 100m; if no pixel is found an error is thrown) and the perimeter_length. iLand ignites the edge of the landscape left/right from the center point at a total length of perimeter_length (m). From this ignited cell the fire spreads using the usual spread algorithm; the maximum fire size is constrained to firesize_m2. If simulate is true no actual fire is simulated, but only the edge detection is executed. The return value is the realized fire size (when simulate is false), or the number of edge cells ignited (when simulate is true). See also the code example at the bottom of the page.

Fire.gridToFile(gridtype, filename)
This function saves a fire specific grid (specified by gridtype) in ESRI raster textfile format to filename. Possible values for gridtype are:

  • basalarea: share of died trees (basal area) on burning pixels (0..1) (RU-Level)
  • kbdi: current values for the kbdi drought index (0..1) (RU-Level)
  • spread: shape of the last burning fire (20m pixels). Non-null numbers indicate the generation counter of the cellular automaton.
  • "border": if allowBurnIn is true, iLand detects edge pixels (20m resolution) and this grid can be retrieved (1=edge, 0=no edge)
  • dbh: average dbh (cm) of burning pixels, limited with the threshold dbh. RU-Level
  • crownkill average crownkill fraction of all burning pixels on RU. (0..1) (see wildfire for details)
  • baseIgnition base probability of an annual fire ignition event for a cell on RU level (depending on fire-return-interval and average fire size)


Fire.grid(gridtype)
Returns a grid of given gridtype (string) as a Javascript Object. See Grid Javascript API for details. All grids (with the exception of the actual spread on the 20m pixels) from the "fire specific visualization" are available.

// save the form of the fire in ESRI raster format
  Fire.gridToFile('spread', 'e:/spread.txt');

Event handler

onAfterFire()
The onAfterFire event handler is called immediately after a fire event. The event handler is set with the fire.onAfterEvent setting in the project file.
Example:

// event handler. Set the fire.onAfterFire to "afterFireProcessing()"
function afterFireProcessing() {
   var praefix = Fire.id;
   // save the form of the fire in ESRI raster format
   // save a file for each fire
   Fire.gridToFile('spread', 'output/fire/spread' + praefix + '.txt');
}


onIgnitionRU
see above.

onCalculateFireSize
see above.

Fire specific outputs

Fire RU/yr

Table Name: fire
Fire event aggregates per fire event. The output contains a row for each (ignited) fire event.

captiondatatypedescription
yearintegersimulation year
fireIdintegerunique ID of the fire event (1..N) on the whole project area.
area_plan_m2integerArea of the planned fire m2
area_m2integerRealized area of burnt cells m2
iterationsintegerNumber of iterations of the cellular automaton
coord_xdoubleCoordinates (x) of the starting point (m)
coord_ydoubleCoordinates (y) of the starting point (m)
n_treesintegertotal number of trees on all burning cells
n_trees_dieddoubletotal number of trees that were killed by the fire
basalArea_totaldoublesum of basal area of trees >4m height (m2) located on pixels that burn during an event
basalArea_dieddoublesum of basal area of died trees (>4m, m2)
psme_dieddoublefraction of doug fir that died (based on basal area of psme trees on burning pixels)
avgFuel_kg_hadoubleaverage total fuel (forest floor + dwd) of burning cells (kg biomass/ha)
windSpeeddoublecurrent wind speed during the event (m/s)
windDirectiondoublecurrent wind direction during the event (°)



Javascript example

The example demonstrates how a table of prescribed fires can be loaded and used in a dynamic simulation.

/* */
var firelist = []; // global variable holding the fires

// load a list of fires from a text file using the CSVFile helper
function loadFires() {
	var csv = Factory.newCSVFile( Globals.path('scripts/fires.txt') );
	for (var i=0;i<csv.rowCount;++i) {
		firelist.push( {
		 year: csv.jsValue(i, 'year'),
		 x: csv.jsValue(i, 'x'),
		 y: csv.jsValue(i, 'y'),
		 area: csv.jsValue(i, 'area'),
		 peri_length: csv.jsValue(i, 'length')
        });
	}
	console.log('Loaded ' + firelist.length + ' fires');
}

// this function is called by the iLand fire module (see the onIgnition handler)
function ignitions() {
	console.log("year " +Globals.year + ": prescribed ignitions");
	// get a subset of all fires 
	var current_fires = firelist.filter( function (item) { return item.year == Globals.year} );
	for (var i=0;i<current_fires.length; ++i) {
		fire = current_fires[i];
		if (fire.peri_length == 0) {
			// this is a fire that starts within the project area
			console.log('** run prescribed fire **');
			Fire.ignite( fire.x, fire.y, fire.area*10000 );

		} else {
			// this is a burn in!
			console.log('** run burn in fire **');
			Fire.igniteBurnIn(fire.x, // x-coord (iLand ref)
							fire.y,  // y coord
							fire.peri_length, // length of perimeter (m)
							fire.area*10000); // max fire size (in m2)
			
		}
	}
}

// set the event handler (onAfterCreate is called automatically from iLand)
function onAfterCreate() {
	// iLand global handler - at this point the fire module is properly set up (and the "Fire" object is available) 
	console.log('setting up fire link');
	loadFires();
    Fire.onIgnition = ignitions;
}


The data table used in the example above:

yearxyarealength
513000159435001000
7472861433000


Notes: "area" is given in ha, and 'x'/'y' in iLand coordiantes. To use GIS coordinates, the value of 'model.world.location.x' and 'model.world.location.y' need to be substracted.

This example shows how the burn-in locations can be "simulated":

Fire.gridToFile('border', 'temp/border.asc'); // save a grid with edge pixels

Fire.igniteBurnIn(12913, 10992, 14000, 1000, true); // start a burn in, with simulate=true
Fire.gridToFile('border', 'temp/border_with_fire.asc'); // save a grid with edge pixels
// now a value of 2 indicates ignited edges (1 normal edges)


citation

Seidl, R., Rammer, W., Spies, T.A. 2014. Disturbance legacies increase the resilience of forest ecosystem structure, composition, and functioning. Ecol. Appl., in press. http://dx.doi.org/10.1890/14-0255.1

Created by werner. Last Modification: Monday 03 of June, 2019 08:31:39 CEST by werner.