SFIRE variables

Back to the WRF-SFIRE user guide.

Introduction

The fire mesh is 2D. Every atmosphere cell is divided into sr_x by sr_y fire cells. The submesh ratios sr_x and sr_y are specified in the file namelist.input. These values are not stored in the NetCDF files, but can be computed from the dimension sizes.

sr_x=west_east_subgrid/west_east_stag = west_east_subgrid/(west_east + 1)
sr_y=south_north_subgrid/south_north_stag = south_north_subgrid/(south_north + 1)

For historical reasons, the fire grid dimensions in the output files are larger than what is actually used by the code internally. The extra space is at the end of the variables of size sr_x in x and sr_y in y. The following is an example of python code for correctly reading FGRNHFX from the file wrfout.

from netCDF4 import Dataset
f=Dataset('wrfout','r')
sr_x=len(f.dimensions['west_east_subgrid'])/(len(f.dimensions['west_east'])+1)
sr_y=len(f.dimensions['south_north_subgrid'])/(len(f.dimensions['south_north'])+1)
fgrnhfx=f.variables['FGRNHFX']
fgrnhfx=fgrnhfx[...,:-sr_y,:-sr_x]

Variables on the fire mesh are located at the centers of the fire mesh cells of a 2D fire mesh.

List of variables

The authoritative information can be always found in the Registry.

State

Variable name	Unit	Description
FXLONG, FXLAT	degrees (real)	longitude and latitude of the nodes (centers of the fire mesh)
	1 (ideal)	mesh coordinates of the nodes; lower left is (0.5,0.5)

Diagnostics

Variable name	Unit	Description
FGRNHFX	J/m2	heat flux from the ground fire

Fire variables on fire grid

Variable name	Dimensions	Stagger	IO	Description	Unit
NFUEL_CAT	*i*j	z	i012hr	fuel data
ZSF	*i*j	z	i012hr	height of surface above sea level	m
DZDXF	*i*	z	i012hr	surface gradient x	1
DZDYF	*i*j	z	i012hr	surface gradient y	1

Fire variables on atm grid (outputs to atm model)

Variable name	Dimensions	Stagger	IO	Description	Unit
RTHFRTEN	ikj	z	hr	temperature tendency	K/s
RQVFRTEN	ikj	z	hr	humidity tendency

Diagnostics

Variable name	Dimensions	Stagger	IO	Description	Unit
AVG_FUEL_FRAC	ij	z	hr	fuel remaining averaged to atmospheric grid	1
GRNHFX	ij	z	hr	heat flux from ground fire	W/m^2
GRNQFX	ij	z	hr	moisture flux from ground fire	W/m^2
CANHFX	ij	z	hr	heat flux from crown fire	W/m^2
CANQFX	ij	z	hr	moisture flux from crown fire	W/m^2
UAH	ij	X	hr	wind at fire_wind_heigh	m/s
VAH	ij	Y	hr	wind at fire_wind_heigh	m/s

Sfire variables on fire grid(also using inputs: zs,z_at_w,dz8w,nfuel_cat,zsf)

Variable name	Dimensions	Stagger	IO	Description	Unit
TIGN_G	*i*j	z	i102hr	ignition time on ground	s
LFN	*i*j	z	i102hr	level function	1
FUEL_FRAC	*i*j	z	i102hr	fuel remaining	1
FMC_G	*i*j	z	i102hr	fuel moisture contents	1
FIRE_AREA	*i*j	z	hr	fraction of cell area on fire	1
UF	*i*j	z	hr	fire wind	m/s
VF	*i*j	z	hr	fire wind	m/s
FGRNHFX	*i*j	z	hr	heat flux from ground fire	W/m^2
FGRNQFX	*i*j	z	hr	moisture flux from ground fire	W/m^2
FCANHFX	*i*j	z	hr	heat flux from crown fire	W/m^2
FCANQFX	*i*j	z	hr	moisture flux from crown fire	W/m^2

Diagnostics for the actual modeled fire

Variable name	Dimensions	Stagger	IO	Description	Unit
ROS	*i*j	z	hr	rate of spread in the normal direction to the fireline	m/s
FLINEINT	*i*j	z	hr	fireline intensity	W/m
FLINEINT2	*i*j	z	hr	alternative fireline intensity	J/m/s^2

Diagnostics for fire risk rating - independent on any actual fire going on

Variable name	Dimensions	Stagger	IO	Description	Unit
F_ROS0	*i*j	z	hr	base rate of spread in all directions	m/s
F_ROSX	*i*j	z	hr	X component of the spread vector driven by wind and slope	m/s
F_ROSY	*i*j	z	hr	Y component of the spread vector driven by wind and slope	m/s
F_ROS	*i*j	z	hr	max spread rate in any direction	m/s
F_INT	*i*j	z	hr	fire reaction intensity for risk rating, without fire	J/m^2/s
F_LINEINT	*i*j	z	hr	Byram fireline intensity for risk rating, without fire	J/m/s
F_LINEINT2	*i*j	z	hr	alternative fireline intensity for risk rating, without fire"	J/m/s^2

Constant data arrays

Variable name	Dimensions	Stagger	IO	Description	Unit
FXLONG	*i*j	z	ihr	longitude of midpoints of fire cells	degrees
FXLAT	*i*j	z	ihr	latitude of midpoints of fire cells	degrees
FUEL_TIME	*i*j	z	hr	fuel
BBB	*i*j	z	hr	fuel
PHISC	*i*j	z	hr	fuel
PHIWC	*i*j	z	hr	fuel
R_0	*i*j	z	hr	fuel
FGIP	*i*j	z	hr	fuel
FZ0	*i*j	z	hr	fuel roughness height
FWH	*i*j	z	hr	fuel fire wind height
ISCHAP	*i*j	z	hr	fuel