环境水文学chapter2-

'March12,2009PrincipleofHydrology,BNU1Chapter2PrecipitationProf.ZongxueXU March12,2009PrincipleofHydrology,BNU2ObjectiveDefinitionandformsofprecipitationSpatialandtemporalattributesTechniquestoestimatearealprecipitation March12,2009PrincipleofHydrology,BNU3WaterVaporandEvaporationEvaporationandwatervaporEvaporation->watervaporincrease->vaporpressureincrease->airvaporpressure=surfacevaporpressure->evaporationceasesSaturatedairspace:Thetemperatureoftheairspaceandwaterareequal March12,2009PrincipleofHydrology,BNU4MeasuresofAtmosphericMoisture/HumidityAbsolutehumidityRelativehumiditySpecifichumidityMixingratioDewpointtemperature… March12,2009PrincipleofHydrology,BNU5PrecipitableWaterDefinition:TheamountofwatercontainedinacolumnofatmosphereextendingupfromtheearthsurfaceEstimation:absolutehumidityW:depthofprecipitablewater(cm) March12,2009PrincipleofHydrology,BNU6FormsofPrecipitationFormsofprecipitationRainSnowHailDrizzleSleetDropletsdiameterSmallone:500-4000μmLargeone:7mm March12,2009PrincipleofHydrology,BNU7FormationofPrecipitationIcecrystalprocessAprocessinwhichcertainparticlesofclaymineralsandorganicandordinaryoceansaltsserveasfreezingnucleiandicecrystalsareformedCoalescenceprocessAprocessbywhichthesmallclouddropletsincreasetheirsizeduetocontactwithotherdropletsthroughcollisions March12,2009PrincipleofHydrology,BNU8PrecipitationTypesConvectiveprecipitationHeatingoftheairatthesurfacewiththegroundUsuallyintropicsForms:showerorstorms(thunderstorms)OrographicprecipitationLiftingofmoisthorizontalaircurrentsovernaturalbarriersImpactfactors:Landelevation,localslope,orientationoflandslope,distancefromthemoisturesource March12,2009PrincipleofHydrology,BNU9PrecipitationTypesCyclonicprecipitationAssociatedwiththemovementofairmassesfromhigh-pressureregionstolow-pressureregionsClassificationFrontalNonfrontal March12,2009PrincipleofHydrology,BNU10ThunderstormsFormation:ThunderstormcellsdevelopfromverticalairmovementsassociatedwithintensesurfaceheatingororographiceffectsThreestages:Cumulusstage:updraft，10-15min.Maturestage:precipitation,15-30min.Dissipatingstage:Downdraft,precipitationends March12,2009PrincipleofHydrology,BNU11PrecipitationVariabilitySpatialdistributionTemporaldistributionSeasonaldistribution March12,2009PrincipleofHydrology,BNU12PointPrecipitationRepresentative:ThedistancefromthegaugetothecenteroftherepresentativeareaThesizeoftheareaThetopographyThenatureofrainfallThelocalstormpatterncharacteristics March12,2009PrincipleofHydrology,BNU13ArealPrecipitationEstimationmethod:ArithmeticmethodIsohyetalmethodThiessenmethod March12,2009PrincipleofHydrology,BNU14IsohyetalMethodDefinitionLinesofequalrainfalldepthConstructionofIsohyetalMapLocateraingaugesandplotvaluesInterpolatebetweengaugesPlotisohyets March12,2009PrincipleofHydrology,BNU15IsohyetalMethodIsohyetMap March12,2009PrincipleofHydrology,BNU16ThiessenMethodConstructionoftheThiessenDiagram:ConnectraingaugelocationsDrawperpendicularbisectorsCalculateThiessenweightsDrawacompletenetworkNotsuitableformountainousareas March12,2009PrincipleofHydrology,BNU17ThiessenMethodThiessendiagram March12,2009PrincipleofHydrology,BNU18PrecipitationMeasurementRaingauge March12,2009PrincipleofHydrology,BNU19ExtensionandInterpretationIntensity:AmeasureofthequantityofrainfallinginagiventimeDuration:Periodoftimeduringwhichrainfalls March12,2009PrincipleofHydrology,BNU20ExtensionandInterpretationFrequency:TheexpectationthatagivendepthofrainfallwillfallinagiventimeArealextent:Theareaoverwhichapoint’srainfallcanbeheldtoapply March12,2009PrincipleofHydrology,BNU21Intensity-DurationRelationshipWorld’shighestrecord:40mm:amin.200mm:20min.26m：ayear March12,2009PrincipleofHydrology,BNU22SummariesTypeofprecipitationPointprecipitationArealprecipitationExtension'