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1、4600JOURNALOFCLIMATEVOLUME24SouthernAfricanMonthlyRainfallVariability:AnAnalysisBasedonGeneralizedLinearModelsCHIARAAMBROSINODepartmentofGeography,UniversityCollegeLondon,London,UnitedKingdomRICHARDE.CHANDLERDepartmentofStatisticalScience,UniversityCollegeLondon,London,Uni
2、tedKingdomMARTINC.TODDDepartmentofGeography,UniversityofSussex,Brighton,UnitedKingdom(Manuscriptreceived7July2010,infinalform23November2010)ABSTRACTSouthernAfricaischaracterizedbyahighdegreeofrainfallvariability,affectingagricultureandhydrology,amongothersectors.Thispaperai
3、mstoinvestigatesuchvariabilityandtoidentifystablerelationshipswithitspotentialdriversintheclimatesystem;suchrelationshipsmaybeusedasthebasisforthestatisticaldown-scalingofclimatemodeloutputs,forexample.Theanalysisusesgeneralizedlinearmodels(GLMs).TheGLMsarefittedtotwentieth
4、-centuryobservationaldatafortheperiod1957–2006tocharacterizethede-pendenceofmonthlyprecipitationoccurrencesandamountsupontheclimateindicatorsofinterest.Incontrastwithmanyoftheanalysesthathavepreviouslybeenusedtoinvestigatecontrolsonprecipitationintheregion,GLMsallowforthei
5、nvestigationoftherelationshipsbetweendifferentcomponentsoftheclimatesystem(geographicalandclimaticdrivers)simultaneously.Sixclimatefactorswerefoundtodrivepartoftherainfallvariabilityintheregion,andtheirmodeledeffectuponrainfalloccurrencesandamountsresultedingeneralagreemen
6、twithpreviousstudies.Amongtheretainedindices,relativehumidityandElNin˜oaccountedforthehighestdegreeofexplainedvariability.Thelocationandintensityofthejetstreamwerealsofoundtohaveastatisticallysignificantandphysicallymeaningfuleffectuponrainfallvariability.1.Introductioninth
7、eregionischaracterizedbyastrongseasonalcyclewithawell-definedwetseason(December–April)overSouthernAfricaisparticularlypronetoadverseeffectsmostofthesubcontinent(Reasonetal.2006).Anoma-ofchangesintheclimatesystem(Christensenetal.2007).louslydrierperiodsduringthewetseasoncomp
8、romiseThevulnerabilityofthesubcontinentisexacerbatedbytheavailabilityofwaterforrain-fedag
