Research Article Setting Wildfire Evacuation Trigg

TransactionsinGIS,2005,9(4):603–617©BlackwellPublishingLtd.2005.9600GarsingtonRoad,OxfordOX42DQ,UKand350MainStreet,Malden,MA02148,USA.ResearchArticleSettingWildfireEvacuationTriggerPointsUsingFireSpreadModelingandGISThomasJ.Cova,PhilipE.Dennison,TaeH.KimCenterforNatural&TechnologicalHazardsDepartmentofGeographyUniversityofUtahMaxA.MoritzDepartmentofEnvironmentalScience,PolicyandManagementUniversityofCalifornia,BerkeleyAbstractWarningcommunitiesinthepathofanadvancingwildfireisachallengingproblem.Decisionmakersneedthemostcurrentinformationavailabletodeterminewhoshouldevacuate,whentheyshouldleaveandwhattypeofordertoissue(e.g.mandatory,recommended,voluntary).ThispaperpresentsanewmethodfordelimitingwildfireevacuationtriggerpointsusingfirespreadmodelingandGIS.Usingdataonwind,topography,andfuelinconjunctionwithestimatedevacuationtime,atriggerbuffercanbecomputedforacommunitywherebyanevacuationisrecommendedifafirecrossestheedgeofthebuffer.AcasestudyispresentedfortheCorralCanyonsectionofthe1996CalabasasFirenearMalibu,California,USA.Thepaperconcludeswithadiscussionofthestrengthsandweaknessesofthisapproach.1IntroductionRecentlargewildfiresinthewesternUnitedStateshavedrawnattentiontothegrowingthreatthatthishazardposestopeopleandpropertyinmanycommunities.In2002,theHaymanFire(Colorado),RodeoFire(Arizona)andBiscuitFire(Oregon)settherecordforthelargestfireineachstate’shistory.Thedevastating2002fireswerefollowedbythe2003SouthernCaliforniaFireComplex,asetoflargefiresinSouthernCaliforniathatresultedin24fatalities,thelossof3,710homes,andtheevacuationofoverahundredthousandpeople(BlackwellandTuttle2003).Oneofthesefires,theCedarFireAddressforcorrespondence:ThomasJ.Cova,CenterforNatural&TechnologicalHazards,DepartmentofGeography,UniversityofUtah,260SouthCentralCampusDrive,Room270,SaltLakeCity,UT84112-9155,USA.E-mail:[e-mail]604TJCova,PEDennison,THKimandMAMoritz©BlackwellPublishingLtd.2005inSanDiegoCounty,wasthelargestfireinCalifornia’shistory.TherecentincreaseintheoccurrenceoflargefiresinthewesternUnitedStatesisgenerallyattributedtofiresuppressionandaccumulatedfuel,althoughlong-termclimatepatterns(Whitlocketal.2003)andshort-termextremefireweatherevents(Moritzetal.2004)areimportantfactorsinmanyareas.Inanycase,decadesofsteadilyincreasingexurbandevelopmentinfire-proneareasgreatlyexacerbatedthehumanimpactofthesefires(Covaetal.2004).Warningcommunitiesinthepathofanadvancingwildfireisachallengingproblem.Emergencyrespondersarrivingonthesceneofaneventmustrapidlyacquireandsyn-thesizeinformationfromavarietyofsourcestoprotectpeopleandproperty.Decisionsaregenerallymadebasedonpersonaljudgmentusinglimitedinformationaboutfirelocationandthreatenedcommunities.Anincidentcommanderneedsthemostcurrentinformationavailabletodeterminewhoshouldevacuate,whentheyshouldleave,andwhattypeofordertoissue(e.g.mandatory,recommended,voluntary).Althoughevacuatingeveryonewouldseemtobethesafestapproach,itisimportanttonot“overevacuate”andsendtoomanyvehiclesontooftenlow-capacityroads(CovaandChurch1997).Ideally,evacuationsshouldbeorderlyandproceedfromthemostthreatenedresidentstotheleastthreatened.Changingwindsandcapriciousfirebehaviorcancom-plicatethisstraightforwardgoal.Emergencyrespondersfacemanydecisionsinfightingawildfire,butthreeimport-antquestionsarisewhenformulatingevacuationorders:whoisatrisk,howlongwillittaketoevacuate,andhowmuchtimeisavailable?Thesequestionsareoftenaddressedtogetherusingaconceptcalledanevacuationtriggerpoint.Atriggerpointisanagreed-uponlandmarkwherebyanevacuationisrecommendedifanadvancingfirecrossesthispoint.Roads,ridgelines,andriversmakegoodtriggerpoints,butanyprominentlandscapefeaturewillsuffice.Triggerpointsaregenerallydeterminedon-the-flyatthetimeofanevent,butcomprehensiveemergencyplansmayidentifycandidatepointsinadvance.Incaseswhenthereisnotenoughtimetosettriggerpointsinfrontofanadvancingwildfire,evacuationordersmaybeissuedimmediatelyuponassessingthesituation.Determiningwhoisatriskandtheestimatedtimetoevacuate(thefirsttwoques-tionsabove)representasignificanthazardsresearchfocus,butlittleworkexistsondetermininghowmuchtimeisavailabletoevacuateacommunityinthefaceofanadvancingwildfire(Kimetal.2006).Researchonthistopicwouldaidinsystematicallyderivingwildfireevacuationtriggerpointsusingageographicinformationsystem(GIS).HURREVACisoneexampleofaGIS-basedsystemthatisusedtosetevacuationtriggerpointsforcoastalareasthreatenedbyhurricanes(FEMA2000).Althoughthisapproachhasnotbeenappliedinawildfirecontext,systematicallyderivingevacuationtriggerpointsusingGIScouldimprovecommunitysafetyinfire-proneareas.Ingeneral,integratingphysicalandsocialprocessmodelstoaidinmanagingemergenciesrepresentsacurrentapplicationchallengeinGIScience(Radkeetal.2000,Cutter2003).Thispaperdescribesanewmethodfordelimitingwildfireevacuationtriggerpointsusingfire-spreadmodelingandGIS.Thefirstsectionofthepaperprovidesbackgroundonevacuationtriggerpoints,evacuationtimeestimationandfire-spreadmodeling.Thenextsectionpresentsamethodforderivingwildfireevacuationtriggerbuffersaroundalo