Fire Weather Science
Fire Weather System Project
EcoConnect-Fire Implementation, June 2013
April 2011
1
NZ Fire Danger Rating System
New Zealand
Fire Danger Rating System
• NZFDRS derived from
Canadian equivalent,
the CFFDRS
Risk of
Ignition
Topography
Fuels
FWI
System
FOP
System
• outputs used to assist
decision-making across
4 Rs of fire management
Weather
AFM
System
FBP
System
NZFDRS
Fire Management
Applications
Reduction
Readiness
Response
Recovery
2
NZFDRS Outputs
Fire danger rating:
“probability of a fire starting,
spreading and doing damage”
Fire potential:
• indication of expected burning
conditions
–
–
–
–
ease of ignition
potential spread rates
fire intensity
fire size and shape
• i.e. fire behaviour
3
Vegetation Fire Environment
• fire behaviour is the product of the environmental
factors which interact with each other and
with the fire itself
• i.e., the “fire environment”:
– topography
– fuel
– weather
Weather
4
NZ Fire Danger Rating System
NZFDRS actually comprised of
a number of subsystems:
• Fire Weather Index (FWI) System
core component
• fire behaviour and fire danger
classes based on Fire Behaviour
Prediction (FBP) System
New Zealand
Fire Danger Rating System
Risk of
Ignition
Weather
Topography
Fuels
FWI
System
FOP
System
AFM
System
FBP
System
NZFDRS
• Fire Occurrence Prediction (FOP)
and Accessory Fuel Moisture
(AFM) subsystems still under
development
5
Fire Weather Index (FWI) System
• numerical ratings of fuel dryness and potential
fire behaviour based solely on weather
− i.e. considers weather component only
• assumes:
− flat ground
− uniform fuels
− reference fuel type
Temperature
Relative Humidity
Wind Speed
Rainfall
Wind
Speed
Temperature
Relative Humidity
Rainfall
Temperature
Rainfall
(dead fuel layers in forest floor
beneath mature pine stand)
• provides relative
indicators of
fire potential
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NZ FWI System
• adopted from Canada in 1980
− developed in similar fire environment
(British Columbia) to NZ
(maritime climate, complex terrain,
mature pine fuels)
• adjusted for use in NZ
− season reversal for Southern Hemisphere
− daylength drying factors for latitude 40°S
− year round calculations
• table and computer calculations
(incl. new FWSYS)
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FWI System
• 4 weather inputs:
− air temperature, relative humidity, wind speed (& wind direction)
and 24-hr accumulated rainfall
− measured at 1200 hr NZST
• 3 fuel moisture codes
Temperature
Relative Humidity
Wind Speed
Rainfall
Wind
Speed
Temperature
Relative Humidity
Rainfall
Temperature
Rainfall
• 3 fire behaviour indices
• higher code and index
values indicate more
severe fire potential
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FWI System – fuel moisture codes
Indicators of relative dryness and availability of different
fuel layers:
Fine Fuel Moisture Code (FFMC)
Temperature
Relative Humidity
Wind Speed
Rainfall
Wind
Speed
Temperature
Relative Humidity
Rainfall
Temperature
Rainfall
− moisture content of fine fuels
− indicates ease of ignition
Duff Moisture Code (DMC)
− moisture content of loose organic
layers & medium woody fuels
− involvement of duff & woody fuels
Drought Code (DC)
− moisture content of compact organic layers & large fuels
− involvement of deep organic fuels
− indicates potential for mop-up problems, and general seasonal dryness
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FWI System – fire behaviour indices
Relative indicators of potential fire behaviour:
Initial Spread Index (ISI)
− combines FFMC and wind speed
− indicates potential spread rate
Temperature
Relative Humidity
Wind Speed
Rainfall
Wind
Speed
Temperature
Relative Humidity
Rainfall
Temperature
Rainfall
Buildup Index (BUI)
− combines DMC & DC
− indicates total fuel consumption
Fire Weather Index (FWI)
− combines ISI & BUI
− indicates potential fire intensity
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Fire Behaviour Prediction (FBP) System
• quantitative estimates of fire behaviour based on
fuels, topography and weather
• predictions of:
−
−
−
−
−
fire spread rates
fuel consumption
fire intensity
fire area & perimeter length
perimeter growth
• assumes elliptical
fire growth
F B P S y s te m
Fuel Type
FFM C,
IS I & B U I,
W in d s p e e d
& d ire c tio n
S lo p e a n g le
&
Aspect
E le va tio n ,
L a t./L o n g .,
D a te
E la p s e d tim e ,
P o in t o r L in e
ig n itio n
FFuueels
ls
W
Weeaath
theerr
TTooppooggra
rapphhyy
FFoolia
liarr
m
moois
istu
ture
re
ccoonnte
tenntt
TTyyppee &&
dduura
ratio
tionn ooff
ppre
reddic
ictio
tionn
FFire
ire BBeehhaavio
viouurr PPre
reddic
ictio
tionn
(F
B
P
)
S
ys
te
m
(F B P ) S ys te m
PPrim
rimaary
ry oouutp
tpuuts
ts::
HHeeaadd fire
fire ra
rate
te ooff sp
spre
reaadd,,
FFuueel l lo
loaadd/co
/connsu
sum
mpptio
tionn,,
HHeeaadd fire
in
te
n
sity,
fire in te n sity,
SSeeccoonnddaary
ry oouutp
tpuuts
ts::
SSppre
a
d
d
ista
n
ce
s,
re a d d ista n ce s,
FFla
lannkk && bbaack
ck fire
fire RRO
OSS && I,I,
AAre
reaa,, PPeerim
rimeete
ter,r,
PPG
GRR aanndd LL/B
/B ra
ratio
tio
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NZ FBP System
• currently 18 identified fuel types
−
−
−
−
−
−
6 plantation forest
2 indigenous forest
2 pasture grassland
2 crop stubble
2 tussock grassland
4 scrub
• models for:
− available fuel loads
− fire spread rates
− slope correction factors
• various tools now available
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NZ Fire Danger Class Criteria
• combines FWI & FBP Systems
• fire danger classes based
on head fire intensity (HFI)
• related to suppression
effectiveness
• models available for Forest,
Grassland and Scrubland
from FBP System
• principal use for notifying
the public
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Fire Danger Class Limits
Fire
Danger
Class
L
M
H
VH
E
Fire
Control
Intensity
Requirements
(kW/m)
< 10
Ground crews with hand
tools
10-500 Ground crews with backpack pumps
500-2000 Water under pressure
and/or heavy machinery
2000-4000 Aircraft using chemical
fire retardants
> 4000 Very difficult if not
impossible to control
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NZ Fire Danger Class Criteria
Temperature
Relative Humidity
Wind Speed
Rainfall
Temperature
Relative Humidity
Rainfall
Wind
Speed
Temperature
Rainfall
Grass Degree of
Curing (%)
Scrubland
Forest
Grassland
G rassland F ire D anger C lass G raph
F orest F ire D anger C lass G raph
30
30
50
25
25
40
20
20
ISI
30
E xtrem e
20
ISI
E x trem e
15
V ery H ig h
10
In itial S p read In d ex (IS I)
E x trem e
Initial S pread Index (IS I)
Wind speed
10-m O pen W ind S peed (km /h)
S crubland F ire D anger C lass G raph
60
15
V ery H ig h
10
H ig h
H ig h
V ery
H igh
M o d erate
10
5
H igh
5
M o d erate
15
Low
L ow
M oderate
Low
0
0
50
60
70
80
F ine F uel M oisture C ode (F F M C )
90
100
FFMC
0
0
20
40
60
80
B u ild u p In d ex (B U I)
100
120
BUI
50
60
70
80
D egree of C uring (% )
90
100
DoC%
New EcoConnect FWSYS
Incorporates latest fire behaviour knowledge:
• new wind speed-Initial Spread
Index (ISI) relationship
– reduced effect at high
wind speeds (>40 km/h)
• new grass degree of curing
(DoC%) relationship
– allows for limited fire spread
below DoC of 50%
• also able to incorporate future
new science (e.g. FWI, curing)
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Daily vs Hourly FWI Values
Standard daily FWI System calculations include in-built
diurnal forecasting
Darfield (FPL)
24
100
• assumes standard diurnal
weather pattern
90
20
80
18
70
16
60
14
12
50
10
40
8
30
6
20
4
Temperature
Wind Speed
2
10
Relative Humidity
0
0
0
3
6
9
12
15
18
21
24
Local Standard Time
– doesn’t always hold,
e.g. frontal change, sea breeze
• hourly FWIs more accurate
– based on actual hourly weather
– hourly FWIs in new FWSYS coming!
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Relative Humidity (%)
• uses 1200 NZST observations
but predicts for peak
burning period (1600 hr)
Temperature ( oC); Wind Speed (km/h)
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Conclusions
• NZFDRS provides outputs that assist
fire management decision-making
• NZFDRS is more than just the FWI System
– FWI is core, but also FBP and FDCC
• Noon daily FWI predicts for mid-afternoon
peak burning period (1600 hr)
– but assumes standard diurnal cycle, will not always be valid
• New EcoConnect-Fire package provides key tool for
accessing important fire weather outputs
– includes latest science, will be updated as new results produced
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