世界银行 -不断变化的洪水风险下的城市扩张与防护缺口 Urban Expansion and Protection Gaps amid Evolving Flood Exposure

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PolicyResearchWorkingPaper11321

UrbanExpansionandProtectionGapsamidEvolvingFloodExposure

JunRentschler

ChristophKlaiber

MengjueZhu

MattiaMarconcini

WORLDBANKGROUP

Urban,DisasterRiskManagement,

ResilienceandLandGlobalDepartmentFebruary2026

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PolicyResearchWorkingPaper11321

Abstract

Floodriskisincreasinggloballyasclimatechangeinteractswithurbanexpansionandland-usedecisionsinfloodzones.Usinganationallyconsistent,high-resolutionassessment,thisstudyanalyzeshowsettlementgrowth,climatechange,andfloodprotectionshapetheevolutionoffloodexpo-sureacrossmorethan11,000municipalitiesinGermany,revealingexposuredynamicsrelevanttomanyadvancedeconomies.Thestudyintegratesbiannualsettlementfoot-printdatafrom2016to2025withfluvial,pluvial,andcoastalfloodhazarddata,futureclimatescenarios,anddetaileddikeprotectionmaps.Theresultsshowthatinseveralregionsthegrowthofsettlementsinfloodzoneshas

outpacedthatinsafezones,thusreinforcingratherthanreducingexposure.Climatechangeisprojectedtoincreasefloodexposuresubstantiallybylatecentury,particularlyunderhigh-emissionsscenarios,withpluvialfloodingbeingthedominantdriveroffutureexposuregrowth.Thestudyidentifiessubstantialmismatchesbetweenexposureandstructuralfloodprotection,withmanyhighlyexposedareaslackingengineereddefenses.Thefindingsunderscorehowmisalignmentbetweenurbandevelopment,climateadap-tation,andprotectioninvestmentcandriverisingfloodrisk,withimplicationsforland-useplanningandresiliencestrategies.

ThispaperisaproductoftheUrban,DisasterRiskManagement,ResilienceandLandGlobalDepartment.ItispartofalargerefortbytheWorldBanktoprovideopenaccesstoitsresearchandmakeacontributiontodevelopmentpolicydiscussionsaroundtheworld.PolicyResearchWorkingPapersarealsopostedontheWebat

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prwp.Theauthorsmaybecontactedatjrentschler@.Averifiedreproducibilitypackageforthispaperis

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ThePolicyResearchWorkingPaperSeriesdisseminatesthefindingsofworkinprogresstoencouragetheexchangeofideasaboutdevelopmentissues.Anobjectiveoftheseriesistogetthefindingsoutquickly,evenifthepresentationsarelessthanfullypolished.Thepaperscarrythenamesoftheauthorsandshouldbecitedaccordingly.Thefindings,interpretations,andconclusionsexpressedinthispaperareentirelythoseoftheauthors.TheydonotnecessarilyrepresenttheviewsoftheInternationalBankforReconstructionandDevelopment/WorldBankanditsaffiliatedorganizations,orthoseoftheExecutiveDirectorsoftheWorldBankorthegovernmentstheyrepresent.

UrbanExpansionandProtectionGapsamidEvolvingFloodExposure

JunRentschler,1ChristophKlaiber,1MengjueZhu,2MattiaMarconcini3,4

1TheWorldBank,WashingtonDC,USA

2GeorgiaInstituteofTechnology,Atlanta,USA

3GermanAerospaceCenter(DLR),Munich,Germany

4Mindearth,Biel,Switzerland

AuthorizedfordistributionbyPeterEllis,PracticeManager,InfrastructureVertical,WorldBankGroup

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Acknowledgments

ThisstudywassupportedbytheTechnicalAssistanceFinancingFacility(TAFF),financedbytheEuropeanCommission—Directorate-GeneralforEuropeanCivilProtectionandHumanitarianAidOperations(DGECHO)—andimplementedbytheWorldBankandtheGlobalFacilityforDisasterReductionandRecovery(GFDRR).ThistechnicalassistancewasdeliveredinpartnershipwiththeGermanFederalOfficeofCivilProtectionandDisasterAssistanceaspartofthe2024TAFFallocationforcountry-specificactivities,underthetitle“ReturnofInvestmentsinDisasterResilienceMeasures:Identifyingmeasures&generatingevidencetoinformdecision-makinginGermany”.ThestudybenefitedfromfeedbackfromPeterEllis,BramkaJafino,andZuzanaStanton-Geddes.

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1.Introduction

Overthepastyears,floodinghasbecomeanincreasinglysignificantconcerninGermany,exacerbatedbychangingriskprofilesduetoclimatechange,landusechange,soilsealing,andsettlementgrowth.Thesefactorscollectivelycontributetoheightenedfloodrisksandchangingfloodhazardzones,posingsubstantialthreatstoboththepopulationandeconomy.Combinedwithexistingvulnerabilities—suchas,butnotlimitedto,lowadaptivecapacity,oldordamagedinfrastructure,remoteness,andhighpovertyrates—thiscanexacerbatethedevastatingimpactsoffloodevents.

ThiswasexemplifiedbythedevastatingAhrtalfloodeventinJuly2021,whichresultedinsignificantlossoflifeandextensivedamagetoinfrastructure;theflashfloodinBraunsbachin2016;andthewidespreadfloodinginsouthernGermanyin2024.Theseeventshighlighttheurgentneedforeffectivefloodriskmanagementstrategies.Climatechangeisalteringprecipitationpatterns,leadingtomorefrequentandintenserainfallevents.Thischangeincreasesthelikelihoodoffloodingandcanevenimpactregionspreviouslyconsideredtobeatlowrisk.Theunpredictabilityoftheseheavyraineventscomplicatesplanningandresponseefforts.

Inadditiontotheimmediatethreattolivesandlivelihoods,floodingposessignificanteconomicchallenges,includingdamagetoinfrastructure,disruptionofbusinesses,andincreasedinsurancecosts.Theeconomicburdenextendstopublicfinances,withsubstantialresourcesrequiredforrecoveryandrebuilding.Long-termeconomicimpactsincludepotentialdeclinesinpropertyvaluesandincreasedcostsforfloodinsurance.

InGermany,managingfloodrisksinvolvescoordinationacrossmultiplelevelsofgovernmentandvariousresponsibleauthorities,eachwithdistinctrolesandresponsibilities.Thefederalgovernmentsetsoverarchingpoliciesandprovidesfunding,whilestategovernmentsareresponsibleforimplementingfloodprotectionmeasures.Localmunicipalities(Gemeinden)playacrucialroleinlanduseplanningandemergencyresponse.

Thismultilayeredgovernancestructurecancreatechallengesincoordination,communication,andultimatelyactionsofresponsibleagencies,particularlyduringemergencysituations.Differencesinprioritiesandresourceallocationbetweenlevelsofgovernmentcanhinderthedevelopmentandimplementationofcomprehensivefloodriskmanagementstrategies.Additionally,theintegrationofscientificresearchandtechnologicaladvancementsintopolicyandpracticerequireseffectivecollaborationbetweengovernmentalbodies,researchinstitutions,andtheprivatesector.Effortstomanagefloodrisksmustalsoconsiderthediverseinterestsofstakeholders,includingresidents,businesses,andenvironmentalgroups.Balancingtheseinterestswhileensuringeffectivefloodprotectionandsustainabledevelopmentrequiresanuancedapproachthatconsidersbothshort-termneedsandlong-termresilience.

Tomanagetheevolvingfloodriskseffectively,accurateinformationoncurrentexposureandsettlementgrowthindifferentfloodhazardzonesisneeded.Thisenablesevaluationsoffederalandregionalpolicies,andregulations,andtoinformzoningplansandpotentialreformsfrom

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planningagencies.ThispaperaimstoshedlightontherecentandprojectedchangesinexposureofGermany’sGemeinden.Weusedataidentifyingtheexpansionofsettlementfootprintsbetween2015and2025incombinationwiththehydrologicalfloodhazardmodelFathom3.Togetherthesedataallowustoidentifyregionaldisparitiesbetweenthefloodexposureofsettlementsandrecentgrowthinfloodandsafezones.Thisenablesvaluableinsightsbetweentheexposuretypes(fluvial,pluvial,andcoastal)ofdifferentdistrictsandfederalstates.Additionally,weusedataonflooddefenseinfrastructuretoidentifyifandwheredevelopmentinhigh-riskareasisprotectedbydikesanddunes.

2.Literaturereviewandinstitutionalcontext

Globally,thereisatrendofincreasingfloodexposure.Thisisprimarilycausedbytwodrivers:first,expandingbuildingfootprintsandsettlementgrowthinfloodzones,andsecond,increasingfrequencyandseverityoffloodandprecipitationevents(Rentschleretal.2023).Floodhazardsalsotendtodisproportionatelyaffectpoorerpeople,puttingthepeopleleastabletodealwithfloodimpactsattheepicenterofincreasingfloodimpacts(Rentschleretal.2022).

SimilardevelopmentsareobservedinGermany,whereheavyraineventsandriverinefloodingareprojectedtobecomemorefrequentwithclimatechange(Langeetal.2020;IPCC2021).Simultaneously,landusechange,soilsealing,andsettlementgrowthhavebeencontributingtoreducedpercolationandincreasedrunoffofrainwater,whichcan,inturn,impactfloodrisk(Umweltbundesamt2025).Overthelast30years,settlementareasandroadinfrastructurehavecontinuouslyincreased;similarly,forestedareashavegrown,whileagriculturallandshares,wetlands,andwatersurfaceshavesteadilydecreased(Seegeretal.2023).

Overthepastyears,floodeventshavehitlargepartsofthecountrywithsomedevastatingoutcomes,sparkinganewdiscussionontheimportanceoffloodprotection.Thecostsofadaptingtochangingclimates—includingfloods,extremeheat,anddrought—areestimatedtoincreaseovertimeto0.6—1.8percentby2050(Flauteetal.2022).

Therecentfloodeventshavepromoteddiscussionsonearlywarningsystemsandfloodprotectionmeasures(FeketeandSandholz2021).Whilethereisanawarenessoftheimportanceoffloodprotection,solutionscangetlostbetweenthedifferentlevelsofgovernment,publicagencies,andtheGemeindenresponsibleforbuildingandzoningplans(Kuhlickeetal.2023).Privatelandownershipisneededforfloodprotectioninfrastructureanditsacquisitionoftendelaynewinfrastructureprojects.Regionalwaterauthoritiesresponsibleforfloodprotectionindifferentstatesoftenpreferconservative,establishedapproachestoacquiringthelandtheyneedforbuildingdikesandpolders(AlbrechtandHartmann2021).So,constructionandplanningtimeframesofnewflooddefenseinfrastructurevarybetweenstates,landacquisitionmethods,andtheregulationsonwhichtheyarebased.

Anotherissueforareasthatarecurrentlyprotectedbyflooddefenseinfrastructureistheuncertaintyrelatedtotheincreasingfrequencyandseverityoffuturefloodevents.Forexample,manystretches

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alongtheGermancoastlineareprotectedbydikes.Underpessimisticclimatechangescenarios,thecurrentlevelofprotectionmightnotoptimizesocialwelfare,butrather,underprotectpeopleandpropertiesalongthecoast(vanderPoletal.2021).Butevenwithincreasedlevelsofinvestment,floodprotectioninfrastructurecannotcompletelyeliminatetheriskofdamage.So,thereisneedtoincreaseawarenessamong,andeducationof,thepubliconlocalizedriskprofiles,earlywarningsystems,andproperty-levelfloodresiliencemeasurestoreducethelong-termimpactoffloodrisks(FeketeandSandholz2021;HudsonandBerghaeuser2023).

Estimatesforcurrentandfutureprojectedfloodexposurevarydependingontheassumptionsandfloodmodelsused.AconservativeestimatebytheGermanInsuranceAssociationisthatatleast300,000addressesareexposedtofloodhazards(GDV2024),whileofficialstatestatisticsestimatethatroughly380,000peopleareexposedtoahighriskofflooding,definedasexposuretoatleast1meterinundationdepthevery10–20years(Stolpeetal.2024).Theestimatesarebasedonthefloodriskmanagementplans,orHochwasserrisikomanagementpläne,

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whicharemandatorytocreateunderEuropeanUnionlaw.InGermany,theseplansaremanagedatthestatelevel,asfloodriskmanagementisorganizedunderindividualfederalstatesandatdistrictandGemeindelevels.Butformajorwatershedsandriversthatflowthroughmultiplestates,river-area-partnerships,orFlussgebietsgemeinschaft,overseethefloodriskmanagementplans.Thisfragmentationanddividedresponsibilitiesmeanthatnationalestimatesarehardertospecify.

Thisstudymakesseveralcontributionstoexistingliteratureandcomplementspriorfindingswithnewanalysis.First,byconsideringfloodexposuretrendswithannualfrequency,ithighlightstheimportanceofmonitoringtheevolvingtrendsoffloodexposuresandshowsthehistoricdevelopmentofsettlementexposurebetween2016and2025usingnoveldata.Second,itshedslightonthedifferencebetweenfloodexposuretypes,whichrequiredifferentflooddefensestrategies.Third,itcombinesexposuredatawithdataonstructuraldefenseinfrastructuretoprovideestimatesformunicipalityprotectionlevels.Andfourth,itprovidesestimatesforpotentialfutureexposurein2050,assumingsettlementfootprintsstayconstantat2025levels,thereforeprovidingalower-boundestimateforfuturefloodexposurenumbers.

3.Dataandmethodology

Thisstudyconsidersthethreemostcommonfloodtypes,whichcanallcontributetourbanfloodhazards:fluvialflooding,whenintenseorexcessiveprecipitationorsnowmeltcauseriverstooverflow;pluvialflooding,whensurfacewaterbuildsupbeyondthesoil’sabsorptivecapacity,owing

1Directive2007/60/ECoftheEuropeanParliamentandoftheCouncilofOctober23,2007,ontheassessmentandmanagementoffloodrisks(FloodRiskManagementDirective;EC-HWRM-RL)enteredintoforceonNovember26,2007.Thedirectivewasimplementedin

GermanybytheWaterResourcesManagementAct(WaterResourcesAct;WHG)ofJuly31,2009(FederalLawGazetteIp.2585)andtheActAmendingtheEnvironmentalAppealsActandOtherEnvironmentalRegulationsofJanuary21,2013(FederalLawGazetteIp.99)intoGermanlaw.Section72WHGdefinestheterm“flood,”andSection75WHGregulatesthepreparationoffloodriskmanagementplans.(LAWA,2019)

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toextendedprecipitationandinsufficientdrainage;andcoastalflooding,owingtowaves,tides,stormsurges,andsealevelchange.

Country-levelpluvial,fluvialandcoastalflooddataarebasedonthe2022Fathom-Global3.0floodhazarddataset(Wingetal.2024).TheFathomfloodhazarddatahavebeenusedextensivelyintheliterature(Rentschleretal.2022;Andreadisetal.2022;Smithetal.2019;Koksetal.2019)andvalidatedindetailedcasestudies,includingfortheUnitedStates,Canada,andtheUnitedKingdom(Sampsonetal.2015;Wingetal.2017).AnothervalidationstudyforNigeriaandMozambique(Bernhofenetal.2018)findsaccuracyratesthatarealignedwith,oronlymarginallylowerthan,thevaluesreportedfortheUK,Canada,andUS.

Thedataprovidegriddedinformationonfloodextentsanddepthsata1-arcsecresolution(equivalentto30metersattheequator),simulating5-,10-,20-,50-,100-,200-,500-,and1,000-yearfloodevents,andareavailableglobally.ThemapsarebasedonMERITDEM,producedbyeliminatingmajorerrorcomponentsfromexistingDEMs(NASASRTM3DEM,JAXAAW3DDEM,ViewfinderPanoramasDEM),includingabsolutebias,stripenoise,specklenoise,aswellastreeandbuildingheightbias,andhavebeenvalidatedextensively(Yamazakietal.2017).

Ourcoreanalysesusethe1-in-100-yearreturnperiodforbothcurrentandfuturescenarios.Forpresent-dayexposureweadditionallyreport10-,50-,and500-yearreturnperiods;5-,20-,and1,000-yearreturnperiodsareusedinrobustnesschecks.Toavoidmisinterpretation,werecallthata“1-in-100-year”eventmeansa1%chanceinanygivenyear—approximatelya10%chanceoveradecadeandabout50%overatypical68-yearlifetime.

Futurefloodhazardsareevaluatedfor2030,2050,and2080understandardCMIP6socio-economicpathways:SSP1-2.6,SSP2-4.5,SSP3-7.0,andSSP5-8.5.Thesescenarioscoupletrajectoriesofgreenhouse-gasemissions,energyuse,landuse,andsocio-economicdevelopmenttodriveclimatemodels,yieldinghazardprojectionsthatspanawidepolicyspace—fromstrongmitigationandinternationalcooperation(SSP1-2.6)toafossil-fuel-intensive,high-emissionsfuture(SSP5-8.5).

High-resolutionsettlementdataareessentialtoquantifyhowhumanexposuretonaturalhazardsevolvesovertime.Inthisstudy,werelyontheWorldSettlementFootprint(WSF)Tracker,developedbytheGermanAerospaceCenter(DLR)(Marconcinietal.,inprep.),whichprovidesbi-annualglobalmapsofbuilt-upareasat10mresolutionfromJuly2016toJanuary2025.TheWSFTrackeristhefirstandonlydatasetworldwidetosystematicallycapturesettlementdynamicsatsub-annualtemporalresolution,enablingnear-real-timemonitoringofurbanizationprocesses.EachepochisgeneratedthroughafullyautomatedworkflowthatintegratesSentinel-1syntheticapertureradar(SAR)andSentinel-2multispectralimagerytojointlyexploitthecomplementarysensitivityofbackscatterandreflectancesignalstobuilt-upstructures.Theclassificationprocesscombinesmulti-temporalstatisticsandmorphologicaldescriptorsextractedfrombothsensorsandappliesahierarchicallearning-baseddecisionframeworktorobustlydiscriminatebuilt-upfromnon-built-upsurfacesunderdiverseenvironmentalandclimaticconditions.Temporalconsistencyisenforcedacrossepochstoensurereliabletrackingofnewconstructionsandpersistenceofexistingsettlements,minimizingspurioustransitions.Theresultingtimeseriesprovidesanunprecedentedcapabilityto

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monitorsettlementexpansionanddensificationpatternsglobally,withdirectimplicationsfordisaster-riskmonitoringandexposureanalysis.Thedatasetissystematicallyupdatedeverysixmonths,andforthisstudyweusedtheversioncoveringuptoJanuary2025,whichwasthelatestavailableatthetimeofanalysis.

Toestimateflood-exposedsettlementareas,thesettlementandfloodhazarddataareoverlaidandcombinedwithadministrativeboundarydatafromHumanitarianDataExchange(HDX2025).TheresultingexposureestimatesareatGemeindeandstatelevel(GemeindeebeneandBundeslandebene,respectively.Inasecondstep,floodexposureiscategorizedintofivegroupsaccordingtoinundationdepthandassociatedrisk:nonexposedareas,andareasexposedtolessthan15,50,150,andmorethan150centimeters.TheresultingestimatesshowhowmuchsettlementareaineachGemeindeisexposedtowhichriskcategory.Basedondatauncertainty,areasexposedtolessthan15centimetersarealsoconsiderednonexposed,ornorisk.Thismethodologyfollowscloselytheestablishedapproachesfromtheliterature(Rentschleretal.2023;Rentschleretal.2022).Toestimatethelevelofprotectiontoriverineandcoastalflooding,weusedataonthelengthofflooddefenseinfrastructuresuchasdikesanddunes.ThesedataareprovidedbytheFederalInstituteofHydrology,BundesanstaltfürGewässerkunde,andcontainthelength,location,name,andreferencebodyofwaterfortheflooddefenseinfrastructure

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Thisstudyadoptsconservativeandcomparablesettingstoprovidedecision-relevant,lower-boundestimatesofexposure.Theflood-protectiondatasetfocusesondikesanddunes;nature-basedmeasuresandothergreyinfrastructure(e.g.,stormwaterdrainage,pumpingstations)arenotyetincluded,whichmeansprotectionmaybeunderstatedwheresuchassetsarepresent.Intheabsenceofdetailedfloodplainconnectivity,theprotectiveeffectofadikeisattributedtotheGemeindewhereitismapped—anattributionthatavoidsoverstatingprotectionacrossadministrativeboundaries.TheWSFTrackertimeseriesspansJuly2016toJanuary2025;forprojections,settlementfootprintsareheldfixedatJanuary2025sothatchangesreflectonlyhazardintensification.Finally,usingFathom3consistentlyforpresentandclimate-conditionedscenariosensuresacoherentbasisforcomparisonwhileacknowledgingtheusualuncertaintiesinterraindata,meteorologicalforcing,andhydraulicparameterization.

Weapproximaterelativeprotectionintensityusingasimpledike-densitymetric:totaldikelengthwithinaGemeindedividedbythesettlementareaexposedtofloodingabove0.15m(1-in-100-yearbaseline).Thisindicatorenableslike-for-likecomparisonsoflineardefensecoverageacrossGemeindenandstates;highervaluessuggestmoreextensivedikecoverageperunitofexposedsettlementarea.Themetricdoesnotcaptureotherprotectionassets(e.g.,duneswherenotmappedasdikes,stormwatersystems,pumping,nature-basedmeasures),northecondition,height,orperformanceofindividualstructures,anditdoesnotresolvefloodplainconnectivityorlocalbottlenecks.Accordingly,weinterpretdikedensitystrictlyasacomparativescreeningindicator—notafullassessmentofoverallprotection.

2Thedatadoesnotcontaininformationontheheightofdikesanddunesandtheprotectionleveltheyprovide.

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4.Results

Inthissection,wepresenttheresultsofahigh-resolutionfloodexposureassessmentforsettlementareasinGermanyatnational,state,andGemeindelevels(thelattercorrespondingtoadministrativelevel3).Theanalysisshowsthattrendsdifferbetweenfloodingtypes,andthatgrowthratesdifferatstatelevels,indicatingdifferencesinregulationsandfloodhazardmitigationimplementationatstatelevel.

4.1.Recenttrendsofsettlementgrowthandfloodexposure

Figure1showsthenationalaggregateforsettlementgrowthinflood-exposedareasatdifferentinundationdepthsfora1-in-100-yearfloodeventbetweenJuly2016andJanuary2025.ThesubplotsoutlinethechangeovertimeforthethreefloodingtypesaswellasasummarygraphplottingthehighestexposureperGemeinde,regardlessoffloodtypeandaggregatingthoseatnationallevel.

Figure1showsthattheexposuregrowthofcoastalfloodingoutpacesotherfloodingtypes.Themostextremecoastalfloodingexposure(>1.5meters)grewbymorethan15percentinaffectedGemeindeninthetimeperiodwhilenon-exposedsettlementareasgrewatarateof8.5percent.Thissuggeststhatinthosethatareexposedtocoastalflooding,settlementsgrewfasterinat-riskareasthaninnonexposedones.Fortheothertwofloodtypes,settlementgrowthinlow-exposedareasoutpacedthatofhighlyexposedareas.Overall,forfluvialandpluvialfloodhazards,thepercentagegrowthofhightoextremefloodexposureshowsasimilarrateofincrease,atroughly8percent;butforpluvialfloodrisk,growthinareaswithexposure<0.15and<0.5metersismoreprominent.

Forthecombinedfloodingscenario,

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thegrowthrateofexposuretothemostextremefloodingdepthisthesecondhighest.Althoughsettlementareasareexpandingfastestinlocationswithlowfloodingrisks(lessthan0.15metersfloodingdepth),thegrowthrateinareasexposedtothemostextremefloodingisnearlythesame(10versus9.5percent).

3Thecombinedfloodscenariocombinesallthreefloodtypesevaluatedinthisstudybyaggregatingtheexposed

settlementareasofthethreehazardcategories,thusprovidingacomprehensiveoverviewof“overall”floodexposureinGermany.

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Figure1:Settlementgrowthrateinflood-exposedareasatnationallevelunderthe100-yearreturnperiodscenario

Note:Percentagegrowthrate=(exposed-settlement-areat–exposed-settlement-areat0)/exposed-settlement-areat0*100;t0isJuly2016.

Figure2providesfurtherinsightintoflood-exposedareasatthestatelevel.Theplotsshowthe

highestfloodriskforeachGemeinde,combiningallfloodtypes,summarizedatthestatelevel.Theorderoftheplotsisbasedonthegrowthrateofexposuretofloodingdepthsgreaterthan0.15

metersbetweenJuly2016andJanuary2025.Thefigureshowsthatnorthernstates,especiallycoastalones,

experiencedahighergrowthrateinfloodexposure.Thisalignswithnationalfindingsshowingthatexposuretohigh-riskcoastalfloodingisthefastest-growingfloodtype.Notably,9ofthe16stateshadthehighestsettlementgrowthratesinareaswithfloodexposureof1.5metersormore.

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Figure2:Growthrateoffloodexposure(%oftotalsettlementarea),byinundationdepthandstate(combinedfloodhazards)

Butifwelookattheincreaseinexposuremeasuredinactualsquarekilometers,andrankthestatesbasedonthetotalincreaseinhigh-riskfloodexposureareas(>0.15meters),weseethat,despitehavingslowergrowthrates,severalnoncoastalstatesranknearthetopintermsoftotalexposedarea.TheseincludeBayern,Niedersachsen,Baden-Wuerttemberg,Nordrhein-Westfalen,Hessen,andRheinland-Pfalz.Table1providesthecorrespondingestimatesforsettlementgrowthinsquarekilometersatstatelevel,orderedbysizeofexposedarea.Lookingattotalexposedareashowsthat,whilesomestates(suchasHessenandRheinlandPfalz)dowellrelativelyintermsofpercentagegrowthofexposedarea,theyrankamongthetopsixstatesintermsoftotalexposedsettlementareainfloodzones.

Figure3showsthefloodexposureofthesettlementareasofall11,111Gemeindenin2025atdifferentinundationdepthsfordifferentreturnperiods.Thesmallerthereturnperiod,themorefrequentthefloodingevent.Notably,foreachreturnperiod,thereareGemeindenwithmorethan50percentofsettlementareaexposedtofloodriskabove15centimeters,andfora1-in-20-yearfloodevent,atleast10percentofGemeindenhaveexposureshareofmorethan6percenttofloodriskabove0.5meters.

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Table1:Summarystatisticsfor