Wildfires & WildlandUrban Interfaceindico.ictp.it › event › a14267 › session › 44 ›...
Transcript of Wildfires & WildlandUrban Interfaceindico.ictp.it › event › a14267 › session › 44 ›...
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Wildfires & Wildfires & WildlandWildland Urban InterfaceUrban Interface
Dominique MORVANDominique MORVAN
AixAix--Marseille University / UMR CNRS 7340 M2P2 Marseille University / UMR CNRS 7340 M2P2
[email protected]@univ--amu.framu.fr
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RoleRole playedplayed by by firesfires in in thethe evolutionevolution ofofspeciesspecies
FireFire470 millions470 millions
yearsyears
GrasslandGrassland--SavanaSavana::
66--7 millions 7 millions yearsyears
TallTall herbivoresherbivoresHomo Homo sapienssapiens
Use (cooking): 1.9 millions Use (cooking): 1.9 millions yearsyearsFull management: 400 000 Full management: 400 000 yearsyears
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WildfiresWildfires in in thethe worldworld
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AverageAverage ofof annualannual burnedburned surface surface aroundaround thethe worldworld
• France: 30 000 ha ,
• Europe: 500 000 ha,
• Australia : 1 200 000 ha,
• USA: 1 500 000 ha,
• Canada : 3 000 000 ha,
• Brasil : + 40 000 000 ha,
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SomeSome historichistoric wildfireswildfires in USAin USA
PeshtigoPeshtigo (Wisconsin, 1871): (Wisconsin, 1871): 2500 2500 deadsdeads et 486 000 ha et 486 000 ha burntburnt
BigBig BlowupBlowup ((IdahoIdaho --MontanaMontana , 1910): , 1910): 87 87 deadsdeads et 1 million ha et 1 million ha burntburnt
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Black Saturday (07/02/2009)Black Saturday (07/02/2009)
Victoria district (Victoria district (AustraliaAustralia))FirestormFirestorm ((KinglakeKinglake ) ) 100 000 ha 100 000 ha burntburnt in 12Hin 12H120 120 deadsdeadsI ~ 80 000 kW/m (>> 7000 kW/m)I ~ 80 000 kW/m (>> 7000 kW/m)20 m = 1600 MW 20 m = 1600 MW (~ (~ oneone elementelement ofof a a nuclearnuclear powerpower plant)plant)ROS ~ 1 ROS ~ 1 àà 3 m/s3 m/sPlume height ~Plume height ~ 15 km 15 km ((lowerlower limitlimit ofof stratospherestratosphere ) )
I = I = η η η η η η η η MMfuelfuel x x ∆∆∆∆∆∆∆∆H x R ~ 300 x HH x R ~ 300 x Hff22
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WildfireWildfire : : catastrophiccatastrophic eventevent or or naturalnatural phenomenaphenomena ??
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EffectEffect ofof smokesmoke on on healthhealth
2010 2010 summersummer : : mortalitymortality x 2 (Moscou)x 2 (Moscou)Fine Fine andand veryvery fine fine particlesparticles (< 10 (< 10 µµµµµµµµm et <2.5 m et <2.5 µµµµµµµµm ) m )
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Statistical data (California)Statistical data (California)NbNb of houses destroyed (wildfire)of houses destroyed (wildfire)
[1955[1955--1985]: 3533 1985]: 3533 [1985[1985--2000]: 7467 2000]: 7467
[2003]: 3710 (cost = 2 Billion $)[2003]: 3710 (cost = 2 Billion $)
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FireFire ecologyecology ((paleoclimatepaleoclimate observations) observations) Wildfires contribute in maintaining forest Wildfires contribute in maintaining forest biodiversitybiodiversityFire regime in various ecosystems:Fire regime in various ecosystems:•• Grassland: 1Grassland: 1 --3 3 ansans•• Conifer forest: 25Conifer forest: 25 --300 300 ansansFire regime:Fire regime:•• Average fire frequencyAverage fire frequency•• IntensityIntensity•• Severity (impact)Severity (impact)•• Fire seasonFire season•• Type (surface fire, crown fireType (surface fire, crown fire ……))•• Average burnt surfaceAverage burnt surface
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FireFire ecologyecology
Factors contributing to modify fire regimes:Factors contributing to modify fire regimes:
Human activities modify fire frequency, inducing Human activities modify fire frequency, inducing soil degradation (washing, soil degradation (washing, lanscapelanscapemodificationsmodifications ……) !) !Impact on ignition rate:Impact on ignition rate:+100 houses +100 houses �������� +0.17 fires/44 +0.17 fires/44 kmkm 22/year/year (USA) (USA) •• Fire exclusion paradigm Fire exclusion paradigm �������� Suppression of low Suppression of low intensity fires intensity fires �������� Fuel aFuel a ccumulationccumulation ��������
IncreaseIncrease ofof highhigh intensityintensity firesfires
LessLess firesfires but more intense but more intense firesfires !!
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WildfiresWildfires causescauses
Anthropic Natural
EuropeEurope 94%94% 6%6%
CanadaCanada 15%15% 85%85%
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LandscapeLandscape evolutionevolution (western USA)(western USA)
189519802001
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WildlandWildland UrbanUrban Interface (WUI)Interface (WUI)
«« IntermixIntermix WUIWUI »» «« Interface WUIInterface WUI »»NaturalNatural vegetationvegetation < 50%< 50%
WUI = houses WUI = houses andand naturalnatural vegetationvegetation are are mixedmixed(>6.17 (>6.17 houses/kmhouses/km 22))
[US [US FederalFederal RegisterRegister JanuaryJanuary 2001]2001]
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WUI (2000) = 9.4% WUI (2000) = 9.4% ofof US US territoriesterritories andand 38.5% 38.5% ofof houseshousesHouses in WUI, Houses in WUI, increaseincrease rate rate [1990[1990--2000]2000] : +44%: +44%
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FireFire regimesregimes in USA in USA
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MappingMapping ofof firefire hazardhazard in USA in USA
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MappingMapping ofof firefire hazardhazard in EU in EU
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Global Global warmingwarming:: surface surface temperaturetemperature change change
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Global Global warmingwarming:: precipitationprecipitation changechange
B1B1 A2A2
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Wildfire hazard in FranceWildfire hazard in France((Commissariat Commissariat GGéénnééralral au au DDééveloppementveloppement Durable, 2011)Durable, 2011)
• Forests = 16 millions d’ha (30% of the territory)• Surface: +20% between 1975 and 2007• 6000 classified communities «potentially affected by wi ldfirehazard »: Corse, La R éunion (100%), PACA (90%), Languedoc-Roussillon (76%), Aquitaine (41%) • Wildfires (average): 30000 ha/an, 4000 ignitions (Va r+Corse = 50% of fires), -2% of fires > 100ha• Var = average burnt surface 1300 ha, 18 800 ha in 200 3 !• Cost (prevention and fight): 536 M € (2008) • Climate change: extension of risky regionsPotentially affected surface 5.5 Mha (2008) ���� 7 Mha (2040) Centre, Poitou-Charentes, Pays de Loire, Bretagne
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Climate change: projection and climate evolution in Climate change: projection and climate evolution in ProvenceProvence Côte Côte dd’’AzurAzur region (summer) (2050) region (summer) (2050)
Projection (Projection ( MMééttééoo France) performed from the France) performed from the moderated scenario (IPCC 2007 B2):moderated scenario (IPCC 2007 B2):
--15%15%--32,9 kg/m32,9 kg/m 22Aquifer deficitAquifer deficit
--38%38%--0.3 mm/j0.3 mm/jPrecipitationsPrecipitations
+ 13%+ 13%+2.9+2.9°°CCTemperatureTemperature
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Ref: Lampin-Maillet (IRSTEA)
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Ref: Lampin-Maillet (IRSTEA)
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MecanismsMecanisms ofof heatheat transfert transfert governinggoverningwildfireswildfires propagationpropagation
Radiation + Convection
Drying, Pyrolyse
Ignition + propagation
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An An otherother mecanismmecanism ofof firefire propagation propagation :: firebrandsfirebrands
Distance Distance travelledtravelled by a by a firebrandfirebrand > 2400 m (source: SALTUS) !> 2400 m (source: SALTUS) !
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Colorado Colorado SpringSpring firefire in 2012in 2012
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Heat flux received by radiationHeat flux received by radiation
( )'' 4
, 1273
1 exp 1862
w f w f f f
f f soot f
q F T T K
L f T
ε σ
ε κ κ
= ≈
= − − × ≈ × ×
ɺ
If fire depth (LIf fire depth (L ff) > 2 ) > 2 -- 3m 3m �������� εεεεεεεεff ~ 1 (black body)~ 1 (black body)FFf,wf,w = view factor flame/target (decreases with distance 1/d= view factor flame/target (decreases with distance 1/d22))
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Ignition criteria (wood)Ignition criteria (wood)
( )1.828'' '' '' 2( 11501 ( ), ( / ))w crit wt q q A A si t s q kW m× − ≥ =ɺ ɺ ɺ
'' 260 31 /wt s q kW m= ⇒ =ɺ
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Maximum heat flux received at 10m by Maximum heat flux received at 10m by
radiation (ICFME)radiation (ICFME)
1.430Ignition (s)
15040Flux (kW/m2 )
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Some characteristic critical heat fluxSome characteristic critical heat flux
31 kW/m 2Wood ignition (60s)
16 kW/m 25s skin exposure (2nd degree burn)
10.4 kW/m 23s skin exposure (pain)
7 kW/m 2Equiped firefighter
2.3 kW/m 22min skin exposure(pain)
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Ignition time (pilot flame)Ignition time (pilot flame)•• Infinite depth materialInfinite depth material
•• Finite depth materialFinite depth material
( )''
0
1 w
ign ign
q
t k c T Tρ≈
−ɺ
( )''
20
1 w
ign ign
q k
t cece T T ρρ≈ ≈
−ɺ
e
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Ignition in pilot flame (FPA)Ignition in pilot flame (FPA)
''
0
ignt
wHeating rate q dt= ∫ ɺPMMA: PMMA: polympolym ééthacrylatethacrylate de de mmééthylethyle((thermoplastiquethermoplastique transparent)transparent)PA6: pine needles (PA6: pine needles ( SimSim ééonioni & al)& al)
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New New toolstools for for simulatingsimulating wildfireswildfiresWFDS: WFDS: WildlandWildland FireFire DynamicDynamic SimulatorSimulator
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FireFire /building interaction in WUI (U/building interaction in WUI (U 1010=1 m/s)=1 m/s)
30 m
20 m
10 m
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HeatHeat flux flux receivedreceived atat Z = 0, 5.5 et 10mZ = 0, 5.5 et 10m
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FireFire /building interaction in WUI (U/building interaction in WUI (U 1010=10 m/s)=10 m/s)
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HeatHeat flux flux receivedreceived atat Z = 0, 5.5 et 10mZ = 0, 5.5 et 10m
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak ::SomeSome empiricalempirical criterioncriterion
( )( )
19642
4 , 1998
FireC
C Flame
LAI DL Emmons
L H Buttlet Cohen
×≥
≥ ×
LC
(Morvan 2015)(Morvan 2015)
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak ::a a numericalnumerical studystudy
( )( )
10
9 18 1964
22 , 1998
5 20
0.75 5 /
C
C
C
Fuel
L m Emmons
L m Buttlet Cohen
L m
H m U m s
≥ −
≥= −
= =
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
16m
8m
6m
3m
> 7 kW/m2 9m
> 16 kW/m2 8m
> 31 kW/m2 5m
T°>373 K the fire was at 23 m from the target (x = 60m , z = 1 m)
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
1
1
1
5920
2700
20000
S
S
S
m
m
m
σ
σ
σ
−
−
−
=
=
=
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
Time = 74 s
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
Time = 88 s
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
Time = 74 s
![Page 48: Wildfires & WildlandUrban Interfaceindico.ictp.it › event › a14267 › session › 44 › contribution › 92 › materi… · Peshtigo (Wisconsin, 1871): 2500 deads et 486 000](https://reader034.fdocuments.net/reader034/viewer/2022042311/5ed93b056714ca7f47696209/html5/thumbnails/48.jpg)
EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
Time = 88 s
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EvaluatingEvaluating thethe efficiencyefficiency ofof a a firebreakfirebreak
![Page 50: Wildfires & WildlandUrban Interfaceindico.ictp.it › event › a14267 › session › 44 › contribution › 92 › materi… · Peshtigo (Wisconsin, 1871): 2500 deads et 486 000](https://reader034.fdocuments.net/reader034/viewer/2022042311/5ed93b056714ca7f47696209/html5/thumbnails/50.jpg)
CharacteristicCharacteristic timetime ofof heatheat transfertransferby convection: by convection: circularcircular cylindercylinder in cross in cross flowflow
( ) ( )0
1/3
( )
4: R P ( , 1996)
ts
s ps s s s s
s ps
s
me r
s
TC h T T T T T T e
tC
relaxation timeh
hNuselt number Nu C Incropera Dewitt
k
τρ σ
ρτ
σ
σ
−∂ = − ⇒ = + −∂
=
= = × ×
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CharacteristicCharacteristic timetime ofof heatheat transfertransferby convection: by convection: circularcircular cylindercylinder in cross in cross flowflow
0.1
1
τ (s)
0.520000 (grass)
55920 (leaves)
τpyr (s)σs (m-1)
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TowardToward a new conception a new conception ofof firefireresistantresistant houses.houses.
RefRef: I. : I. WeirWeir QueeslandQueesland UniversityUniversity ofof TechnologyTechnology(Australie).(Australie).
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ThankThank youyou for attentionfor attentionQuestions ?Questions ?