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FEARLUS-W:AnAgent-BasedModelofRiverBasinLandUseandWaterManagementL.R.Izquierdo,N.M.GottsandJ.GaryPolhillMacaulayInstitute,Craigiebuckler,Aberdeen.AB158QHl.izquierdo@macaulay.ac.uk,n.gotts@macaulay.ac.uk,g.polhill@macaulay.ac.uk:thefirstchancetouse(andperhapsabstractorpollute)thewater.Theflowingnatureofwatercreatesasymmetriesintheinteractionsbetweenusers.FEARLUS-Wisaspatially-explicitagent-basedmodelbuilttoincreaseourunderstandingofthesecomplexinteractionsandexplorehowcommon-poolresourceproblemsinriverbasinmanagementmightbetamedthroughsocio-economicinteractionsbetweenstakeholders(primarilyrurallandmanagers),andthroughmanagementstrategiesaimedatshapingtheseinteractions.FEARLUS-Wisbeingconstructedwithinanextendedversionofanexistingspatially-explicitagent-basedmodeloflandusechange,FEARLUS(Polhill,GottsandLaw,2001),drawingontheoriesofcommon-poolresourceuse,andonsurveyworkamongstakeholders.ThemainextensionstoFEARLUSdealwithwater,waterflowandwaterpollutionontheonehandandallowforagentswithmultipleandpotentiallyconflictingtop-levelgoalsontheother.FEARLUS-W:AnAgent-BasedModelofRiverBasinLandUseandWaterManagementIntroduction__________________________________________________1Cleanwaterasacommon-poolresource___________________________2Whyagents?_________________________________________________3TheexistingFEARLUSmodel___________________________________4Context:theWaterFrameworkDirectiveproject_____________________5ModellingCPRdilemmas:thesymmetricalcase_____________________6Agentswithmultipledimensionsofutility__________________________8Representingsocialapproval___________________________________8Thedecisionmakingalgorithm_________________________________9Water,waterflowandwaterpollution:theasymmetricalcase_________12Conclusions_________________________________________________17Acknowledgement___________________________________________18References__________________________________________________181IntroductionWhatthereforeNaturehathjoinedtogether,letnotScienceputasunder.Inrecentyears,theneedtoimproveourunderstandingofhowthesocio-economicandecologicalaspectsoftheworldsysteminterweaveincoupledsocio-ecosystemshasbecomeincreasinglyobvious.Inwatermanagementinparticular,theimpactofhumanactivityonwaterbodiesissooverwhelming,andtheimportanceoftheecologicalstatusofwaterbodiesforsocietyissocrucial,thatanintegratedapproachisparticularlynecessary.Alreadyin1992,theUnitedNationsConferenceonEnvironmentandDevelopmentheldinRioacknowledgedthateconomicscouldnotbeseparatedfromthemanagementofwaterresources:“Integratedwaterresourcesmanagementisbasedontheperceptionofwaterasanintegralpartoftheecosystem,anaturalresource,andasocialandeconomicgood”(UN,1992).Environmentalissuesingeneralarecharacterisedbycomplexinteractionsbetweensocietiesandtheecosystemstheyoccupy.AsWeisbuch(2000)pointsout,thereisaloopofinteractionsbetweentheagents’cognitivepropertiesandtheirimmediateenvironment.Ononehand,agentstakedecisionsaccordingtotheirbeliefs,whicharedeterminedbytheperceivedstateoftheirimmediateenvironment.Ontheotherhand,eachagent’sdecisionsinfluenceotheragents’viewsdirectlyand,atagloballevel,theychangethestateoftheecosystemasawhole.Theimportanceofthesecomplexinteractionsisboostedinthecaseofwaterresourcesduetothepresenceofharmfulexternalitiesandthecrucialroleofthephysicalspace.Harmfulexternalitiesappearwhenevertheutilityofoneagentisaffectednegativelybytheactionsofanotheragent.Thepresenceofstrongharmfulexternalitiesislikelytoleadtoeconomicsociallyinefficient1levelsofappropriation,sinceindividualsdonotusuallyvalueotherindividuals’benefitsasmuchastheirown.Moreover,whenratherthananagentaffectingdirectlyotherfewagents’utility,theexternalitiestakeplacethroughtheenvironment,harmisoftenspreadoutandthefullconsequencesofagents’actionsonotherindividualsareoftenunderestimatedbytheactors.Inparticular,damagingtheenvironmentcanreducetheutilityofagentswhowerenotappropriatingtheresource.Thesituationofsociallyefficientresourceuseisusuallyhighlyunstable.Theinstabilitystemsfromthefactthatindividualsmighthaveanincentivetomoveawayfromthesociallyefficientoutcomeandfromthefactthattheactionsofonesingleindividualcanhavedevastatingconsequencesforthegroup,bothdirectlyandthroughsocialinfluence.Henceitisconvenienttorepresentindividualsexplicitlyinourmodels.1Anoutcomeiseconomicsociallyefficientifitimpliesanoptimumdegreeofutilisationoftheresourcefromtheperspectiveofthe