FloodRiskChange AComplexityPerspective
AndreasPaulZischg UniversityofBern,Bern,Switzerland
Elsevier
Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates
Copyright 2023ElsevierInc.Allrightsreserved.
Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorage andretrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowto seekpermission,furtherinformationaboutthePublisher’spermissionspoliciesandour arrangementswithorganizationssuchastheCopyrightClearanceCenterandtheCopyright LicensingAgency,canbefoundatourwebsite: www.elsevier.com/permissions .
Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightby thePublisher(otherthanasmaybenotedherein).
Notices
Knowledgeandbestpracticeinthis fieldareconstantlychanging.Asnewresearchand experiencebroadenourunderstanding,changesinresearchmethods,professional practices,ormedicaltreatmentmaybecomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgein evaluatingandusinganyinformation,methods,compounds,orexperimentsdescribed herein.Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafety andthesafetyofothers,includingpartiesforwhomtheyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,or editors,assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatter ofproductsliability,negligenceorotherwise,orfromanyuseoroperationofanymethods, products,instructions,orideascontainedinthematerialherein.
ISBN:978-0-12-822011-5
ForinformationonallElsevierpublicationsvisitourwebsite at https://www.elsevier.com/books-and-journals
Publisher: CandiceG.Janco
AcquisitionsEditor: AmyM.Shapiro
EditorialProjectManager: JoshuaMearns
ProductionProjectManager: KumarAnbazhagan
CoverDesigner: GregHarris
TypesetbyTNQTechnologies
Tomyfamily,Heike,Jule,andLinus
Thispageintentionallyleftblank
Analyzingspatiotemporaldynamicsoffluvialerosionand riverbedaggradation112
Analyzingchangesinfloodexposure119
Analyzingtheeffectsoflanduseplanningonfloodexposure125
Modelingtheeffectsofchangingvulnerabilityonfloodriskchange128
Analyzingtheeffectsoffeedbackandtimelagsonflood riskchange 134
Feedbackeffectsoffluvialerosionandriverbedaggradationon floodriskchange134
Feedbackeffectsoflandscapeshapingfloodeventson hydrologicalchange141
Feedbackeffectsoffloodeventsontheinitiationofflood protectionprojects146
Thesocietalmemoryeffectonhouseconstructionactivitiesin flood-proneareas148
Timelagsintheimplementationoffloodriskmanagement measures151
Otheraspectsthatarecontributingtothecomplexityofflood riskmanagement153
4.Riversandfloodplainsascomplexadaptivesystems?
5.Modelingspatiotemporaldynamicsofflood
Thetool“Flooddamagepotential”190
Thetool“Flooddamagesimulator”198
Thetool“Floodriskdynamics” floodriskchangeatcentennial scale214
Thetool“Flooddynamics” floodimpactvariabilityathourly scales225
Decision-makingleadstotheemergenceofspatialpatternsof floodriskchange242 Monitoringfloodriskchange247
Modelingframeworkforconsideringcomplexityinthe analysisoffloodriskchange
Thispageintentionallyleftblank
Preface
Thebookemergedfromtwodifferentexperiences,frompracticalexperiencein moderatingparticipativeplanningprocessesinfloodriskmanagementandfrom theresultsofmyresearchinfloodrisk.Iworkedforseveralyearsasaconsultant forpublicadministrationsthatareresponsibleforfloodprotectionandwater resourcesmanagement.Planningandimplementingfloodprotectionmeasures requiretoinvolvepersonsfromdifferentsectorsanddisciplines.Floodprotectionmeasuresneedspacetoenlargerivers.Therefore,landowners inmany casestheagriculturalsector arestakeholdersintheplanningprocess.Moreover,stakeholdersfromenvironmentalprotection,hydropowerproduction, tourism,localrecreation,monumentpreservation,cityplanning,landscape ecology,archeology,landscapeesthetics,waterresourcesmanagement,and individualresidentsmaybeinvolvedintheplanningprocess.Thisresultsina diversityofperspectivesonthetopicorontheprojectandinavarietyofinterests andexpectationsfortheplanningprocess.Balancingtheinterestconflictsor targetconflictsinparticipatoryplanningprocessesandfindingacommonsense overthepossiblesolutionswiththegrouptosolvetheproblemsareoneofthe keychallengesforexpertsinfloodriskmanagement.Discussionsinsuchdiverse groupsshedlightontheinterdependenciesbetweenthedifferentsectorsand problems.Simplesolutionsthatmaysolveonesingleisolatedproblemaffect manyotherproblems,positivelyornegatively,ormayresultinunintended consequencesornewproblems.Therefore,possiblesolutionsforthefloodrisk managementproblemhavetosatisfyalsotheexpectationsofotherplanning targets.Thismakessuchplanningprocessescomplexandverychallenging. However,whenadoptingacomplexityperspectiveonthistopic,wecan approachtheproblemswithapositiveattitude.Insteadofbeinganobstaclefor implementingfast-forwardandsimplisticsolutionsforanarrowlydefined problem,diversitybecomesthekeyforfindingsustainableandrobustsolutions.I experiencedmanytimesthattheinclusionofmultiplestakeholdersandtheir perspectivesintheplanningprocessledtoholisticsolutions.Inmanycases,the commonlyelaboratedsolutionsforfloodriskmanagementsolvedalsoother problemsthatareconnectedwiththefloodriskmanagementproblem.The foundationsofcomplexsystemsresearchcanprovidethebasisforanew thinkingandthusprovidehelpintacklingcomplexandwickedproblems.
Witheachfloodprotectionproject,weadaptourenvironmentandlandscape toourneeds.Togetherwithnaturalchangesintheenvironmentandclimate,
thesehumanadaptationsshapetherelationshipsbetweenhumansandtheir environment.Allthreecomponentsoffloodrisk hazard,exposure,and vulnerability arechanging.Thismakesthatfloodriskischangingdynamically inspaceandtime.Asuccessfulandsustainableadaptationtofuturefloodhazards isonlypossibleifweconsiderthemaindriversofchangingrisks.Wemustknow whereandhowtointerveneforkeepingfloodrisksconstantintime,oreven reducingit,alsounderincreasinghazards,increasingexposure,andincreasing vulnerability.Again,thecomplexityperspectivesupportstheanalysisofthe dynamicnatureoffloodrisks.Complexsystemsscienceprovidestheoretical foundationsforanalyzingchange,numerosity,feedbacks,nonlinearbehavior, emergence,systembehaviorandsystemsensitivity,anddeepuncertainty.
Thebookaddressestwotypesofreaderships.Expertsandengineersworking infloodriskmanagementmayfindsomeideasofhowtoconsiderandtackle complexityintheirprojects.Scientistsmayfindideasandconceptsforanalyzing floodriskchange.InChapter1,thetopicoffloodriskchangeisintroduced. Chapter2 summarizesandexplainsthekeydriversoffloodriskchange. Chapter3 highlightsapproachestoshowhowthecomplexinteractionsbetween thecoevolvingdriversoffloodriskchangecanbedisentangledandhowthe isolatedeffectsofsingledriversofchangeonoverallfloodriskevolutioncanbe quantified. Chapter4 discussesthequestionifriversandtheirfloodplainscanbe interpretedascomplexadaptivesystems. Chapter5 describesexamplesofmodel experimentsforanalyzingthespatiotemporaldynamicsoffloodriskchange.The lastchaptersummarizestheconclusionsofthemodelexperimentsbylookingat thetopicoffloodriskchangefromtheperspectiveofcomplexadaptivesystems.
Thebookcovertellsthestoryofchangingfloodriskinamountainousriver catchment.Apreviousfloodeventtriggerednewfloodprotectionmeasures,in thiscasetheheighteningofthelateralprotectivewalls.Floodriskwaslowered foratime,butthequestionishowlongitwilltakethatthefollowingincreasein exposureandvulnerability,aswellastheincreaseinhazardintensityand probabilityduetoclimaticchanges,willincreasefloodriskagaintopreadaptationlevels.Thecovershowsalsothattherearelimitstoadaptationbyafurther heighteningofthelateralprotectivewallsinthefuture.Thebookisafirststep intotheanalysisofthedynamicnatureoffloodrisks.Itfollowsasystemic approach includingenvironmental,socioeconomic,andsociotechnical factors formodelingandmanagingfloodriskchange.Readerswillgetamore completepictureofthetopicforunderstandingthecomplexityoffloodrisk change,bothfromhumanandnaturalcausesofflooding.
Chapter1
Introduction
Floodriskchange:Acomplexityperspective.Thistitlecoverstwomaintopics ofthisbook.Thefirstandmaintopicisfloodriskchange.Floodsarestillone ofthemostdamagingnaturalhazards,accountingforthemajorityofall economiclossesfromnaturalhazardsworldwide(UNISDR:MakingDevelopmentSustainable:TheFutureofDisasterRiskManagement,2015).Risk resultingfromfloodsisdefinedasafunctionoftheprobabilityofafloodevent orscenarioanditsrelatedextentofdamage.However,asweareenteringin theeraof“GreatAcceleration”(Steffenetal.,2015),socioeconomyandthe humanenvironmentarechangingrapidly.Withtheseglobalchanges,every singlefactorthatcontributestofloodrisksischanging.Thisresultsinahighly dynamicchangeinfloodrisks.
Lookingathowfloodriskischangingorevolvinginspaceandtimerequiresaparadigmchange.Mostoftheproblemswearecurrentlydealingwith resultfromsolutionsofproblemsofthepast.Manydecisionsweretakeninthe pastwithoutforeseeingpossiblefuturedevelopmentpaths.Thebuiltenvironmentcreatedwilllastforalonglifecycle,anditshapestheadaptation optionsoffuturegeneration.Floodriskmanagersarestillplanningstructural floodprotectionmeasuresunderaverystaticperspective.Whenconductinga riskanalysis,webecomeasnapshotintimeandspace.Wedonotknowthe trajectoryandthechangerateofthepastfloodriskevolution.Evenless,we canforeseefuturedevelopmentsoffloodrisk.
Forthis,thesecondtopicofthebooktitleopensanewperspectiveonflood risks.Insteadofconsideringfloodriskasstaticintimeandspace,thebook aimsatshowinghowfloodriskcanchange.Thebookintendstosummarize thewaytowardanewunderstandingoffloodrisks.Thiscomprehendstolook athowthedriversofrisk,thefactorsofrisk,andtheresultingrisksare changing.Thechangesofthesingleriskfactors hazard,exposure,and vulnerability arenotindependentfromeachother.Changesinfloodhazards areinfluencingandtriggeringchangesinhazardandvulnerability.Therefore, wecanlookatfloodriskchangewithasystemicperspective.Inanalyzingthe dynamicchangesoffloodrisk,wecanobservemanyfeaturesofcomplexity, namelytheemergenceofpatterns,feedbackmechanisms,numerosityand diversity,orderanddisorder,nestedstructures,modularity,multiplescales, hierarchies,nonlinearity,episodicalchanges,historyandmemory,pathdependency,andadaptivebehavior.Thesecharacteristicsofcomplexsystems
canbeobservedintheevolutionofcoupledhumanandnaturalsystemsand mustbeconsideredinfloodriskmanagement.Inthisbook,Ithereforewantto lookatchangingfloodrisksfromthecomplexityperspective.Thebookisa primerforanalyzingandmodelingfloodriskchange.Itpavesawaytoward thedevelopmentofmodelingframeworksthatareabletoconsiderselected aspectsofcomplexity.Thisisabsolutelyneededtoavoidunintendedconsequencesofdecisionsincurrentfloodriskmanagementinthelong-term perspective.Thebookshouldgiveanoutlookonhownew-generation modelingapproachescanrepresentthecomplexbehaviorsoffloodplains andcoupledhumanandnaturalsystemsinahighlydynamicenvironment. Thesetoolsandmethodsshouldhelpfloodriskmanagementpracticetotackle withincreasinglywickedproblems.
Floodrisksarenowincreasinglybeinganalyzedfromadynamicrather thanfromastaticperspective(Mazzoranaetal.,2012; Merzetal.,2010). Severalstudieshaveaddressedchangesinnaturalrisksoverrecentdecades andcenturies(Himmelsbachetal.,2015; Hufschmidtetal.,2005; Paprotny etal.,2018),andresearchonclimatechangeanditsimpactshasfocusedon futurechangesinrisks(Alfierietal.,2016, 2017; Arnell&Gosling,2016; Dottorietal.,2018; Hirabayashietal.,2013).However,moststudiesfocused solelyonthefutureincreaseinfloodhazard.Onlyfewstudiesconsiderboth theimpactsofclimaticchangestoriverflowsandthefuturedynamicsinthe elementsatrisk(Bouweretal.,2010; Jongmanetal.,2012; Liuetal.,2015; Loschneretal.,2017; Winsemiusetal.,2016).Closerexaminationsofthe spatiotemporaldynamicsandtheactualrateofchangeareratherrare. Knowledgeabouthazardousprocessesandtheirimpacts,aswellasaboutthe trajectoriesoffloodriskchanges,isessentialforthesustainablemanagement offloodrisks.
Severalintertwinednaturalandanthropogenicdriversinfluencethe spatiotemporalevolutionoffloodrisk.Inthisbook,thefollowingdriversof floodriskchangethatarerelatedtoenvironmentalchangesareconsidered:
l Floodsareeithercausedbydirectrainfallonthefloodplain(pluvialfloods andsurfacewaterfloods)orrainfallonrivercatchmentsresultingin catchmentoutflow.Thelattercausesfloodsindownstreamfloodplains (riverinefloodsandlakefloods).Consequently,changesinfloodprocesses, i.e.,changesinfrequencyandmagnitudeoffloodsinafloodplain,are determinedbychangingprecipitation.
l Inmountainousareas,floodhazardsareinfluencedbysedimenttransport anddepositionprocessesanddebrisflows.Debrisflowsareinfluencedby environmentalchanges,suchasmeltingofglaciersandpermafrost,or changesinweatheringprocessesandmassmovements.
l Rivermorphologychangesovertime,includingnaturalandgradual changesintherivermorphology,ordisruptivechangesbyfloodevents.An importantaspectofrivermorphologychangesisanthropogenic
interventions,whicharerelevantdriversoffloodriskinafloodplain,for example,theconstructionofflooddefensessuchasleveesanddamsor riverrestorationprojects.However,theconstructionofleveesasflood protectionmeasuresinonefloodplaincanhaveadverseeffectsinthe downstreamfloodplainsandcanresultinfloodingtrade-offsbetweenupstreamanddownstreamfloodplains.
Besidechangesinthenaturalenvironment,floodriskisalsoevolvingdue tochangesintheexposedelementsatriskandtheirvulnerability.Fromthis aspect,thefollowingdriversofchangeareconsideredhere:
l Theincreaseintheelementsatriskchangeduetosocioeconomicdevelopment.Thegrowthofsettlementsandthustheincreaseofresidential buildingsarerelatedtopopulationgrowth.
l Infrastructureisincreasinginparallelwithpopulationgrowth.Thishas widerimpactsonthesocioeconomicsystem.Forexample,ineconomically activeareas,floodplainsareincreasinglyoccupiedbyproductionfacilities, astheserequirerelativelyflatareasfortheirconstruction.Witheconomic development,theelementsatriskandtheinfrastructureinfloodplainsare increasingbothintermsofquantityandmonetaryvalue.
l Increasingvaluesatriskcompetewithopposingdriversoffloodrisk reductionmeasuresimplementedbyindividualsandthepublic.Hence, changesinexposureandvulnerabilityareinfluencedbygovernmental interventionsandregulationsandbytheactionsofindividuals.
Thebuiltenvironmentinfloodplains,whetherthesettlementareaorthe riverchannel,issubjecttochangesandcoevolutionarydynamicsinbothsocietyandnature(DiBaldassarreetal.,2013, 2015; Fuchsetal.,2017).As Vitouseketal.(1997) postulated,thehumanimpactonnatureisnow considerablylargerthanatanypointinhistory.Thisistrueforthefloodplains, ashumansareshapinglandscapeswiththebuiltenvironment.Theseimpacts ofsocietyonnatureinfluencespathwaysoffloodriskchange.Thespatiotemporaldevelopmentofthesedriversofchangeinfloodriskleadstodifficultiesinpredictingfuturefloodrisk.Consequently,recentstudieshave extendedtheframeworkofriskanalysistowardaspatiotemporalframeworkas driversforfloodriskchangesarevaryinginspaceandtime(Ahmad& Simonovic,2013; Zischgetal.,2018).Thisbookgoesonestepfurtherand showsexamplesofmodelexperimentsthatanalyzefloodriskchange,the driversoffloodriskchange,orfeaturesofcomplexity.Welookatfloodrisk fromadynamicperspective.Thereaderwillbecomehands-onexamplesof howwecananalyzepastchangesinfloodrisk,ofhowwecanmonitor changingrisks,andofhowwecanmodelfloodriskchangesbyconsidering complexinteractionsbetweenthedriversofchange.
Chapter2 summarizesandexplainsthekeydriversoffloodriskchange. Thechapterbeginswithdefinitionsoffloodrisksandexplainshowfloodrisk
canbecalculatedfromtheriskfactorshazard,exposure,andvulnerability.It describeshowsystemscanbedelimitedandrepresentedinriskanalyses.The focusislaidonriversystemsandfloodplains.Intheseareas,floodhazards meettheanthropogenicelementsatriskandtheirvulnerability.Riversystems andfloodplainsevolveintime.Thechapterdescribesthemainfactorsthat shapethelong-termevolutionoffloodplainsandoffloodrisk.Itprovidesan overviewofallfactorsthatarerelevantfortheincreaseordecreaseofflood risks,rangingfromenvironmentalchange,climaticchange,andsocioeconomicchange.Afterdescribingtheisolatedeffectsofthesingledriversof change, Chapter2 endswithadescriptionofcoevolutionofriskfactors. Moreover,aninsightintospatiotemporaldynamicsoffloodriskchangeis givenbyexplainingwherechangesinthesystemcomponentsoccurandwhere thesebecomerelevantforfloodriskchange.Herein,upstream downstream andariverbasin riverreachrelationshipaswellaslegacyeffectsintimeand spaceareexplained.
Chapter3 highlightstheoreticalandmethodologicalapproachestoshow howthecomplexinteractionsbetweenthecoevolvingdriversoffloodrisk changecanbedisentangledandhowtheisolatedeffectsofsingledriversof changeonoverallfloodriskevolutioncanbequantified.Aspecialfocusislaid onthepotentialofmodelexperimentsforanalyzingfloodriskchange.Thus, principlesofframeworksforanalyzingandmodelingfloodriskchangeare explained.Thechapterintroducesseveralexamplesofmodelexperimentsthat aimatdisentanglingtheeffectsofselecteddriversofchangetooverallflood riskevolution.Aspecialexampleshowshowfloodriskschangedwithinthe past300yearsaftertheearlygeoengineeringprojectoftheKanderRiver deviationintheCantonofBern,Switzerland.Thiscasestudyshowshowa cascadeofunintendedconsequencesforthesocietycanbecausedbyahuman interventioninthenaturalriversystem.Moreover,thiscasestudyalsopoints outhowdifficultalong-termperspectiveistokeeponfloodriskmanagement. Thetechnologicaladvancementoftheindustrialrevolutiontotallychangedthe frameworkofsociety’svaluesthatunderlinedecision-makinginfloodrisk management.Thepresentedcasestudiescanbeusedtocomparetheeffectsof environmentalchangesandtheeffectsofhumaninterventionsonfloodrisk evolution.Itbecomesclearthatfuturefloodriskevolutioncanradicallybe shapedbyhumanadaptationandintervention.Oneexampleclearlyshowsthat theimplementationoffloodpreventionmeasuresremarkablydrivesfloodrisk reduction.Themodelexperimentbasesmainlyoncounterfactualsimulations, i.e.,comparingthepresent-daysituationwithalternativepathwaysofnatural andsocietaldevelopment.Someofthecasestudiesexemplifyhownegative feedbackeffectswillcontributetofloodriskreductionalthoughclimatic changesmightincreasetheintensityandfrequencyofextremeprecipitation events.Herein,sedimentsupplyorsedimentdeficitdeterminesfloodrisk changeinmountainareas.Inthelastpart, Chapter3 showsanalysesonthe effectsoflanduseplanningandtimelagsinthelanduseregulationon
emergingpatternsofriskhotspotsinthelongterm.Moreover,itpresents examplesoftheeffectsofthedecliningsocietalmemoryofpastfloodevents onfloodexposureandvulnerability.
Chapter4 arguesifthelong-termevolutionofriversandtheirfloodplains canbeinterpretedascomplexadaptivesystems.Tothisend,themainfeatures andcharacteristicsofcomplexsystemsaresummarized.Thischaptersheds lightonthenatureofthecoupledhumanandnaturalsystemsoffloodplains andidentifieswhichcharacteristicsofcomplexsystemscanbeobservedon floodplains.Thereaderwillgetananswertothequestioniffloodriskin floodplainsisacomplicatedissueoriffloodplainscanbeconsideredasa complexsystemorasacomplexadaptivesystem;or,ifriversandfloodplains arenowadaystobeconsideredassociotechnicalsystemsratherthannatural systems.Theseanswershelpthereadertounderstandtheemergentphenomenainthelong-termdevelopmentoffloodplains.Examplesofpastflood eventswillbediscussed,andtheywillbeshownhowtheseeventsinfluenced policy,technology,andriskawareness.Viceversa,exampleswillshowhow pasttechnologicalinnovationsshapedriversandfloodplains.Thechapterends withanoutlookonpossiblefuturetrajectoriesandpathwaysoffloodrisk evolutionandwithadiscussionofthesensitivityoffloodplainstoclimatic changes.
Chapter5 describesexamplesofmodelexperimentsandanalysesof spatiotemporaldynamicsoffloodriskchange.Itexplainsfiveinteractiveweb toolsthathavebeendevelopedbytheMobiliarLabforNaturalRisksofthe OeschgerCenterforClimateChangeResearchoftheUniversityofBernin Switzerland.Thefirsttoolsupportscitizensciencethataimsatcollecting geolocalizedimagesandphotographsoffloodevents.Thisgrowingdatabase canbevisualizedandqueriedinaweb-basedmapapplication.Itcontributesto keepingthesocietalfloodmemoryalive.Thesecondtooldescribesaninteractiveweb-mappingapplicationthatestimatesthenation-wideexposureof buildings,residents,workplaces,andcriticalinfrastructuretofloods.Itcontributestotheunderstandingofthedifferencebetweenahazard-centeredand anexposure-centeredvisualizationoffloodrisks.Thethirdtoolgoesonestep furtherandprovidesaninteractivemodelexperimenttotestthesensitivityof flooddamagestourbandensification,theimplementationofproperty-level floodprotectionmeasures,andstructuralfloodprotectionmeasuresinthe riverchannel.Thistoolaimstoshowhowonedesiredeffectofurbanplanning, namelytoprioritizetheinternaldensificationofcitiesbydevelopingunusedor abandonedspacesagainsturbansprawl,potentiallycanresultinanunintended increaseoffloodrisks.Itfurthermoreshowshowexistingfloodriskscanbe reducedbyimplementingfloodpreventionmeasuresbydifferentstakeholders. Fourth,amodelexperimentisdescribedandimplementedinaninteractive web-basedapplicationthatallowstoassessthetrajectoryoffloodriskchange inafloodplaininthepasttwocenturies.Theusercantestcounterfactual scenariosofurbandevelopmentandofalternativefloodriskmanagement
strategies.Moreover,theusercantesttheeffectsofdifferentdriversofchange totheoverallfloodriskevolution.Thistoolcontributestotheunderstandingof thedynamicnatureoffloodrisksinspaceandtime.Thefifthtoolshows storylinesofextremerainfalleventsandtheirimpacts.Theuserofthis interactivewebapplicationcannavigatethroughthespatiotemporalevolvementofafloodeventwithatimesliderandzoominandoutatdifferentscales. Thistoolvisualizesdirectandindirecteffectsoffloodeventsatanhourly timescale.Ithelpstounderstandthecomplexpatternsofrainfalleventsovera complexmountaintopography,howtheimpactsoftheeventonsocietyare evolvinginspaceandtime,namelyfromupstreamtodownstream,andhow thespatialfootprintofthefloodimpactsfollowstherainfallpatternwithatime lag. Chapter5 isalsodescribingamodelexperimentthatshowshowthe philosophicalschoolthatisbehinddecision-makinginfloodriskmanagement canleadtotheemergenceofpatternsinfloodriskhotspots.Itshowshowthe considerationornonconsiderationsofsocialjusticeaspectsinprioritysetting canpotentiallyguidethedistributionofpublicfundsforinvestmentsinflood protectiontowardremoteandeconomicallydisadvantagedortoward economicallyadvantagedregions.Finally,thelastexampledescribesthe operationalizationofaninformationsystemformonitoringfloodriskchange. Chapter5 summarizestheprinciplesofmodelcouplingforanalyzingand modelingfloodriskchange.Itdiscussestheadvantagesorlimitationsof coupledcomponentmodels.Thesemodelshaveapotentialforconsidering featuresofcomplexsystemssuchasfeedbacks,adaptivebehavior,structural change,regimechange,andnonlinearbehavior.Thechaptercloseswitha summaryofthelessonslearntduringthedevelopmentofseveralcoupled componentmodelsandtheimplementationofthemodelexperimentsthat weredescribedinthepreviouschapters.Itcloseswithaperspectiveontheuse ofcoupledcomponentmodelsinhydrologyandinthesimulationofcoupled humanandnaturalsystems.
Thelastchaptersummarizestheconclusionsofthemodelexperimentsand analysesdescribedinthisbookbylookingatthetopicfromtheperspectiveof complexadaptivesystems.Itdiscussesrecommendationsofhowtoconsider andimplementsomethoughtsofcomplexsystemsscienceintofloodrisk managementpracticeandinthedevelopmentofnext-generationsimulation models.Thisaimsatenablingmodeler’sanddecision-makerstoanalyzethe bigtrendsorfuturepathwaysoffloodriskevolutionbyconsideringhuman behaviorinsimulationsoratleastbycouplingmodelsforsimulatinghuman behaviorwithmodelsforsimulatingnaturalprocesses.Thischaptershows howfloodriskmanagementcanbeenhancedwiththeperspectiveofcomplex systemsscience.Itwillshowhowurgentlyweneedtoconsiderthecomplex interactionsbetweenthedriversofchangeandcomplexityinfloodriskanalysesanddecision-makinginfloodriskmanagement.Finally,thechapter outlinesacomplexityperspectiveforgoverningfloodriskchangeinthe21st century.
Withallthis,thebookscrapsthesurfaceofanewperspectiveandanewset ofmethodstotacklethecomplexproblemsoftheAnthropoceneandto confrontdeepuncertainties.
References
Ahmad,S.S.,&Simonovic,S.P.(2013).Spatialandtemporalanalysisofurbanfloodrisk assessment. UrbanWaterJournal,10(1),26 49. https://doi.org/10.1080/ 1573062X.2012.690437
Alfieri,L.,Bisselink,B.,Dottori,F.,Naumann,G.,deRoo,A.,Salamon,P.,Wyser,K.,& Feyen,L.(2017).Globalprojectionsofriverfloodriskinawarmerworld. Earth’sFuture, 5(2),171 182. https://doi.org/10.1002/2016EF000485
Alfieri,L.,Feyen,L.,&DiBaldassarre,G.(2016).Increasingfloodriskunderclimatechange:A pan-Europeanassessmentofthebenefitsoffouradaptationstrategies. ClimaticChange, 136(3 4),507 521. https://doi.org/10.1007/s10584-016-1641-1
Arnell,N.W.,&Gosling,S.N.(2016).Theimpactsofclimatechangeonriverfloodriskatthe globalscale. ClimaticChange,134(3),387 401. https://doi.org/10.1007/s10584-014-1084-5
Bouwer,L.M.,Bubeck,P.,&Aerts,J.C.J.H.(2010).Changesinfuturefloodriskduetoclimate anddevelopmentinaDutchpolderarea. GlobalEnvironmentalChange,20(3),463 471. https://doi.org/10.1016/j.gloenvcha.2010.04.002
DiBaldassarre,G.,Kooy,M.,Kemerink,J.S.,&Brandimarte,L.(2013).Towardsunderstanding thedynamicbehaviouroffloodplainsashuman-watersystems. HydrologyandEarthSystem Sciences,17(8),3235 3244. https://doi.org/10.5194/hess-17-3235-2013
DiBaldassarre,G.,Viglione,A.,Carr,G.,Kuil,L.,Yan,K.,Brandimarte,L.,&Bloschl,G.(2015). Debates Perspectivesonsocio-hydrology:Capturingfeedbacksbetweenphysicalandsocial processes. WaterResourcesResearch,51(6),4770 4781. https://doi.org/10.1002/ 2014WR016416
Dottori,F.,Szewczyk,W.,Ciscar,J.C.,Zhao,F.,Alfieri,L.,Hirabayashi,Y.,Bianchi,A., Mongelli,I.,Frieler,K.,Betts,R.A.,&Feyen,L.(2018).Increasedhumanandeconomic lossesfromriverfloodingwithanthropogenicwarming. NatureClimateChange,8(9), 781 786. https://doi.org/10.1038/s41558-018-0257-z
Fuchs,S.,Rothlisberger,V.,Thaler,T.,Zischg,A.,&Keiler,M.(2017).Naturalhazardmanagementfromacoevolutionaryperspective:ExposureandpolicyresponseintheEuropean Alps. AnnalsoftheAmericanAssociationofGeographers,107(2),382 392. https://doi.org/ 10.1080/24694452.2016.1235494
Himmelsbach,I.,Glaser,R.,Schoenbein,J.,Riemann,D.,&Martin,B.(2015).Floodriskalong theupperRhinesinceAD1480. HydrologyandEarthSystemSciencesDiscussions,12, 177 211. https://doi.org/10.5194/hessd-12-177-2015
Hirabayashi,Y.,Mahendran,R.,Koirala,S.,Konoshima,L.,Yamazaki,D.,Watanabe,S.,Kim,H., &Kanae,S.(2013).Globalfloodriskunderclimatechange. NatureClimateChange,3(9), 816 821. https://doi.org/10.1038/nclimate1911
Hufschmidt,G.,Crozier,M.,&Glade,T.(2005).Evolutionofnaturalrisk:Researchframework andperspectives. NaturalHazardsandEarthSystemScience,5(3),375 387. https://doi.org/ 10.5194/nhess-5-375-2005
Jongman,B.,Ward,P.J.,&Aerts,J.C.J.H.(2012).Globalexposuretoriverandcoastalflooding: Longtermtrendsandchanges. GlobalEnvironmentalChange,22(4),823 835. https:// doi.org/10.1016/j.gloenvcha.2012.07.004
Liu,J.,Hertel,T.W.,Diffenbaugh,N.S.,Delgado,M.S.,&Ashfaq,M.(2015).Futureproperty damagefromflooding:Sensitivitiestoeconomyandclimatechange. ClimaticChange,132(4), 741 749. https://doi.org/10.1007/s10584-015-1478-z
Loschner,L.,Herrnegger,M.,Apperl,B.,Senoner,T.,Seher,W.,&Nachtnebel,H.P.(2017). Floodrisk,climatechangeandsettlementdevelopment:Amicro-scaleassessmentofAustrian municipalities. RegionalEnvironmentalChange,17(2),311 322. https://doi.org/10.1007/ s10113-016-1009-0
Mazzorana,B.,Levaggi,L.,Keiler,M.,&Fuchs,S.(2012).Towardsdynamicsinfloodrisk assessment. NaturalHazardsandEarthSystemScience,12(11),3571 3587. https://doi.org/ 10.5194/nhess-12-3571-2012
Merz,B.,Hall,J.,Disse,M.,&Schumann,A.(2010).Fluvialfloodriskmanagementinachanging world. NaturalHazardsandEarthSystemScience,10(3),509 527. https://doi.org/10.5194/ nhess-10-509-2010
Paprotny,D.,Sebastian,A.,Morales-Na ´ poles,O.,&Jonkman,S.N.(2018).Trendsinfloodlosses inEuropeoverthepast150years. NatureCommunications,9(1). https://doi.org/10.1038/ s41467-018-04253-1
Steffen,W.,Broadgate,W.,Deutsch,L.,Gaffney,O.,&Ludwig,C.(2015).Thetrajectoryofthe anthropocene:Thegreatacceleration. AnthropoceneReview,2(1),81 98. https://doi.org/ 10.1177/2053019614564785
UNISDR.(2015).Makingdevelopmentsustainable:Thefutureofdisasterriskmanagement.In Globalassessmentreportondisasterriskreduction,4.2015.UnitedNations.
Vitousek,P.M.,Mooney,H.A.,Lubchenco,J.,&Melillo,J.M.(1997).Humandominationof Earth’secosystems. Science,277(5325),494 499. https://doi.org/10.1126/ science.277.5325.494
Winsemius,H.C.,Aerts,J.C.J.H.,vanBeek,L.P.H.,Bierkens,M.F.P.,Bouwman,A., Jongman,B.,Kwadijk,J.C.J.,Ligtvoet,W.,Lucas,P.L.,vanVuuren,D.P.,&Ward,P.J. (2016).Globaldriversoffutureriverfloodrisk. NatureClimateChange,6(4),381 385. https://doi.org/10.1038/nclimate2893
Zischg,A.P.,Hofer,P.,Mosimann,M.,Ro ¨ thlisberger,V.,Ramirez,J.A.,Keiler,M.,& Weingartner,R.(2018).Floodrisk(d)evolution:Disentanglingkeydriversoffloodriskchange witharetro-modelexperiment. ScienceoftheTotalEnvironment,639,195 207. https:// doi.org/10.1016/j.scitotenv.2018.05.056
Keydriversoffloodriskchange
Thetermfloodriskisheredefinedaccordingthegeneralconceptofdisaster riskoftheIntergovernmentalPanelonClimateChangeIPCC(IPCC,2012). Disasterriskisdefinedasthe“likelihoodoveraspecifiedtimeperiodofsevere alterationsinthenormalfunctioningofacommunityorasocietydueto hazardousphysicaleventsinteractingwithvulnerablesocialconditions, leadingtowidespreadadversehuman,material,economic,orenvironmental effectsthatrequireimmediateemergencyresponsetosatisfycriticalhuman needsandthatmayrequireexternalsupportforrecovery.”Thus,riskrequiresa potentialhazard(H)andthe“presenceofpeople;livelihoods;environmental servicesandresources;infrastructure;oreconomic,social,orculturalassetsin placesthatcouldbeadverselyaffected.”Thisisdefinedasexposure(E). Moreover,exposedpeople,communities,andinfrastructuremustbevulnerabletothehazard.Vulnerability(V)isthe“propensityorpredispositionof exposedpeopleorinfrastructuretobeadverselyaffected”(IPCC,2012).Risk iscomposedofthesethreemaincomponents.Thus,riskisafunctionof hazard,exposure,andvulnerability(UNISDR,2015)andisoftenexpressedin Eq.(2.1)
Thesethreemaincomponentsofriskarenotindependent.Exposureis connectedwiththemagnitudeandprobabilityofthehazardousevent.The higherthemagnitudeofthehazard,thehigheristhenumberofexposed populationorinfrastructure.However,thisinteractionisnonlinearanddependsonmanyfactors,whichwillbediscussedbelow.Thevulnerabilityof exposedassetsalsodependsonthefrequencyandmagnitudeofthehazardas wellasonthecharacteristicsoftheexposedobjects,andthusthereisan interactionbetweenthesecomponentsofrisk.Themainreasonofthisinterdependencyismostlyduetotheeffectsofsociallearning.Buildingsand infrastructurebuiltnearriverswithfrequentfloodshaveoftenareduced vulnerabilitybecausetheyhavebeenadaptedtothehazardafterprevious events(Elmeretal.,2010; Kienzleretal.,2015).Theconsiderationofthree maincomponentsindefiningriskopensthepossibilitytoconsiderhuman interventionsforriskreduction.Theseinterventionscanrangefromthe installationofconcretehydraulicengineeringstructurestomeasuresfor avoidingurbanizationinhazardousareasbylanduseplanningorbuilding
R ¼ H E V
(2.1)
flood-proofinfrastructurewithreducedvulnerability.Thefirsttypeofinterventionstargetsatreducingthehazard H,eitherintermsofreducingfrequencyormagnitudeoffloodevents.Thesecondtypeofinterventiontargetsat reducingexposure E,andthethirdtypeofinterventionsaimsatreducing vulnerability V.
Thecalculationofriskwithorwithoutriskmanagementmeasuresleadsto theassessmentandquantificationoftheefficacyofthesemeasuresintermsof riskreduction.Thecomparisonofthebenefitswiththecostsoftherisk reductionmeasuresallowstoanalyzetheefficiencyofriskreductionmeasures.However,thisrequiresthemonetizationofrisks,i.e.,quantifyingthe riskandthereducedriskaftertheimplementationofriskreductionmeasures inmonetaryunits.Innaturalsciencesandengineering,riskisquantifiedasa measureofuncertaintybasedontheconceptofprobability.Thus,riskisthe probabilityofalosswithinacertaintimeperiod.Asthelossdependsonthe magnitudeandfrequencyofthehazardtriggeringtheloss,theprobabilityof occurrenceofahazardeventorscenariowithacertainmagnitudeistakenas theprobabilityoftheloss.Thus,eventriskorscenarioriskcanbewrittenas shownin Eq.(2.2) (Oberndorferetal.,2020).
Where Ri,j istheriskdependentonobject i andscenario j, pj istheprobability ofdefinedscenario j, pi,j istheprobabilityofexposureofobject i toscenario j, Ai isthevalueofobject i affectedbyscenario j,and vi,j isthevulnerabilityof object i independenceonscenario j.Theprobabilityofscenario j isthe probabilityofoccurrence,mostlysimplifiedbythenumberofhowoftenthe eventofthismagnitudepotentiallyoccurswithinaspecifiedtimeperiod.This isalsotermedasthereturnperiodofanevent.Ifahazardeventofacertain magnitudeisexpectedtooccuroncein100years,itiscalleda“1-in-100years event”ora“100yearevent.”Ifthevalueofobject i isexpressedinmonetary termsandthevulnerabilityisadimensionlessdegreeoftheobjectsuffering loss,theriskfunctionisamultiplicationandresultsintheprobabilityofa damageevent(Eq.2.3).
Theterm“loss”heredefinesthequantifiableaspectsofharmanddamage thatresultfromahazardevent.Inthisway,thescalarvalueofriskincludes bothprobabilityandtheseverityoftheimpact,butinawaythatkeepshazard, exposure,andvulnerabilitydistinctandgivesrisetoasingledimension (Rougieretal.,2013).Theterm“damage”isusedforexplicitlyfocusingon themonetizedimpactsofhazardeventsandthusisasubsetoftheoverallloss. Ifmultiplehazardscenariosareconsideredinthequantificationofrisk,risk orthemeanexpectedloss inmanycasesina1-year-interval isthesumof theproductofeachpossiblelossanditsprobability.Thelossesofseveral
Ri;j ¼ pj pi;j Ai;j vi;j (2.3)
hazardscenarioswithincreasingmagnitudesanddecreasingoccurrence probabilityformthelossexceedanceprobabilitycurve(Fig.2.1).Innatural hazardsmanagement,thisfunctionisoftentermedasthe“hazardfootprint” function.Thefootprintfunctionaggregatesthespatialoverlaybetweenthe footprint(s)ofthehazardscenario(s)andthevaluesatriskwiththeirobjectspecificvulnerabilities.Theformandshapeofthefootprintfunctionshow howthelossincreaseswitheventmagnitude. Fig.2.1 showsanexampleofa floodhazardfootprintfunctionintermsofexposedpopulation.Ifriskis derivedfromtheexceedanceprobabilitycurveorfromthefootprintfunction, riskiscalculatedasthemeanlossfromtheareaunderthecurve.Fromtherisk changeperspective,itbecomesobviousthatriskquantificationmustinclude thetimeperiodforwhichthefootprintfunctionandtheassessedriskvalueare valid.
Principlesoffloodriskanalysis
Asthisbookdealsmainlywithfloodrisksinmountainousorhillyterrain,the procedureofanalyzingfloodriskisoutlinedschematicallyinthefollowing section.Theconceptisdescribedfroma“top-down”perspective,byfollowing thecourseofthewaterthroughthelandscape.
Themainstartingpointisthedefinitionofthehazarddomainandthe spatialdelimitationofthesystemthatisconsideredintheriskanalysis.The
FIGURE2.1 Hazardfootprint.Anexampleofahazardfootprintfunctionshowingthe relationshipbetweenincreasingfloodmagnitudeandincreasingfloodexposure. Modifiedfrom Zischg,A.P.,&Bermu´dez,M.(2020).Mappingthesensitivityofpopulationexposuretochanges infloodmagnitude:Prospectiveapplicationfromlocaltoglobalscale. FrontiersinEarthScience, 8 https://doi.org/10.3389/feart.2020.534735
firststepisthedefinitionofthehazardprocess.Inthecaseoffloods,thereare severalpossibilitiestoconsider.Probablythesimplestfloodhazardintermsof directcausaleffectfromheavyrainfalltoconsiderinfloodriskanalysisis floodingfrominfiltrationexcessoverflow,i.e.,surfacerunoffleadingtosurfacewaterfloods.Floodsbysurfacerunoffresultfromrainfalleventsthat exceedtheinfiltrationcapacityofthesoil.Inurbanenvironmentswithahigh shareofsealedsurfaceandlimitedsewercapacity,thethresholdofrainfall intensityandsumfortriggeringsurfacewaterfloodsarelower.Thisprocessis alsotermedaspluvialfloods.Inthiscase,thespatialdelimitationofthesystem equalstheareaforwhichtheriskmustbecalculated(areaofinterest)orfor whichriskreductionmeasuresareplannedplusthe(small)catchmentsfrom whichsurfacewaterisflowingintotheareaofinterest(Fig.2.2,left).Incase ofriverinefloods,thespatialdelimitationofthesystemconsideredforrisk analysisisthefloodplainwherethesettlementsorinfrastructurearelocated (areaofinterest)plustheupstreamwatershedorriverbasin,whichcontributes tothedischargeintheriverthatistriggeringfloodeventsintheareaofinterest (Fig.2.2,right).Inlargerriverbasins,therecanbeseveralareasofinterestif morethanonefloodplainexists.Inthiscase,theareasofinterestforrisk analysisarenestedwithintheriverbasin.
Insummary,thesystemdelimitationcomprisesthetypeofhazard consideredinthestudy,theareaofinterestwheretheriskhastobeanalyzed, andtheupstreamareaswherethehazardprocessesoriginatefromandformthe boundaryconditionoftheinnersystem.Theinnersystemcanbedefinedasan opensystem.Hazardscanoriginateandoccurwithinthesystemitselfandcan enterintothesystemfromoutsideatthesystemboundary.Theoutersystem delimitation,i.e.,theupstreamcatchmentarea,isthusneededformodelingthe hazardincaseoffloods.
Besidessurfacewaterfloodsandriverinefloods,floodhazardsarealso influencedbyotherfloodprocessessuchassedimenttransport,lateralerosion, largewoodtransportanddeposition,aswellasdebrisflow.Especiallyin
FIGURE2.2 Systemdelimitation.Spatialdelimitationofthesystemconsideredinfloodrisk analysis.Left:theareaofinterestforriskanalysisplusthecontributingareasforsurfacewater floods.Right:theareaofinterestplustheupstreamcatchment.Backgroundmapfrom map.geo.admin.ch.
mountainousareas,floodsandtheirimpactsoninfrastructurearelikely dominatedbysedimenttransportanddeposition.Thus,thedefinitionofthe systemforwhichtheriskanalysisisvalidcontainsaclearstatementforwhich typeofhazardtheriskanalysisisvalid.Thisispartofthesystemdelimitation. Thisexplicitdefinitionofthehazardprocessesconsideredandtheexplicit exclusionofthehazardtypesthatarenotconsideredarenecessaryforthe interpretabilityoftheresults.Especiallyiftheriskanalysisistermedas“flood riskanalysis,”misunderstandingsormisinterpretationscanresultfromunclear definitionsofthefloodprocesstype.Anotherrequirementofthesystemdelimitationisaclearstatementofwhichtypeofexposureisconsideredinthe riskanalysis.Istheriskassessmentvalidforpeople,buildings,orinfrastructureonly?Aremobileassetsas,forexample,carsmovingaround consideredintheanalysis?Dependingonthetypeofassetconsidered,the systemcanbespatiallylimited,butitisopentoinputfromoutside.One exampleofanopensystemisroadtrafficenteringandexitingthefloodplains.
Inmostcasesoffloodriskanalysis,theareaofinterest(innersystem)isa floodplainorasetoffloodplainswithinariverbasin.Infloodplains,themain factorsoffloodrisk,thefloodprocess,andthevaluesatriskintersectspatially. Fromaphysicalperspective,floodplainsaredefinedasareasoflandadjacent toandformedbyflowingwaterintimesoffloods.Fromasocioeconomic perspective,floodplainsprovidelandforsettlement,infrastructure,andother humanactivities.Inthefollowing,theterm“floodplain”isusedsynonymously fortheareaofinterestforfloodriskanalysisifnototherwisespecified.
Oncethetypeofhazardandexposureisdefinedandthesystemisspatially delimited,themainhazardinputparametersforestimatingtheprobabilityand magnitudeofthehazardeventsandscenariosaredetermined.Thecalculation offloodriskrequiresasetofeventsorscenarioswithincreasingmagnitude. Thisistheso-called“eventset.”Inanidealcase,thecasestudyareahasalong recordofwell-documentedfloodevents.Thespatialfootprintsofthesepast floodeventscanbereconstructed(Bomersetal.,2019)andoverlaidwiththe actualorhistoricdatasetofexposure,e.g.,housesortrafficinfrastructure.If theoccurrenceprobabilityofthereconstructedfloodeventscanbedetermined, thehistoriceventsetleadstothelossfootprintfunctionofthesystemunder investigation.Eventually,riskcanbequantifiedfromthisfootprintfunction.
However,theeventsetisverysmallinmanycases,duetotheinherentlow probabilityofoccurrenceofextremeevents.Inthissituation,theeventset mustbedevelopedbymeansofsimulationmodelsorbyacascadeofsimulationmodels.Thefirststepfordeterminingtheeventsetforsurfacewater floodsistoanalyzethecharacteristicsofrainfallevents(Bernetetal.,2019). Themeteorologicaldatafromnearbylocatedmeteorologicalstationsis analyzedwithextremevaluestatistics.Anintensity-durationfunctionis derivedfromthedataandasetofrainfallscenarioswithincreasingmagnitude isderivedfromtheextremevaluestatistics.Thissetofrainfallscenariosthen isusedasaninputformodelingsurfacewaterfloods.Thehydrodynamic
