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Snow Hydrologyhydrology Importanceimportance Ofof Snowsnow Soso What?What? FieldField MethodsMethods inin SnowSnow HydrologyHydrology ImportanceImportance ofof snowsnow SoSo what?what? The water of the world • Oceans: 97.24 % • Polar Ice: 2.15% • Groundwater: 0.61% • Lakes: 0.17% • Soil moisture: 0.005% • Atmosphere: 0.0001% • Rivers: 0.00001% • * There is a total of 0.78511% of the worlds water that is fresh and not frozen! (not all is available for use, and in fact, very little is useable) • Add: ½ groundwater, lakes, rivers and you have: 0.47501% of the worlds water available for use • • * In some areas, 50% of the surface water is polluted and non-useable. Realistically, we may have only 0.25% available for use. Terrestrial Cryosphere On average, 60% of the Northern Hemisphere has snowcover in midwinter. Over 30% of the Earth’s land surface has seasonal snow. About 10% of the Earth’s surface is covered permanently by snow and ice. Seasonally and permanently frozen soils occur over ~35% of the Earth’s land surface. Spatial extent of frozen and thawed areas vary significantly on daily, seasonal, annually, and interannual time scales. SoSo what?what? A. Effect of snow cover on climate – Albedo-reflectivity (new snow ~0.8-0.9, older snow ~0.5-0.6). Compare this to ice 0.3-0.4, forest 0.03-0.2, and water 0.05- 0.3 Result: blocks incoming radiation from heating the surface so solar radiation is returned to space instead of being retained as heat in the atmosphere. Strong climate effects: – Surface temperature-stay depressed over snow. – Ground temperatures-with low thermal conductivity, snow serves as an insulator and keep vast area of soil unfrozen. • Climate feedbacks- more snow decreases temp which cause more snow which will persist longer. SoSo what?what? B.B. ImportanceImportance inin waterwater resourcesresources • Controls the hydrologic cycle- water is stored over the winter and released in a pulse during the spring melt. Present difficulties for water managers, reason for existence of reservoirs. • Frozen water = 80% of fresh water on earth • Major contributor to river and ground water in mid/high latitudes. Ex. Seasonal snowcovers- western US: CA 80% of water, Co 70% of water. SoSo what?what? C. Avalanches – impacts on backcountry and mountain residents: • Estimated to be 100,000 in the US on average, ~ 10,000 reported and 100 or 1% are problematic – property damage, injury, death. • Damage to buildings and structures – only $1/2 million per year in US, but much higher in Europe because of dense populations. SoSo what?what? •• SnowmeltSnowmelt floodsfloods areare aa severesevere problem:problem: – Red River of the North, April 1997 • $4 Billion in Damages – Northeast Floods, January 1996 • Delaware R., Hudson R., Ohio R., Susquehanna R., Potomac R. • 33 Deaths, $1.5 Billion in Damages SnowSnow HydrologyHydrology UnderstandingUnderstanding andand predictingpredicting thethe physicalphysical processesprocesses of:of: •• SnowSnow AccumulationAccumulation •• AblationAblation •• MeltMelt WaterWater RunoffRunoff SnowSnow HydrologyHydrology 44 SimultaneousSimultaneous EstimationEstimation ProblemsProblems –– thethe quantityquantity ofof waterwater heldheld inin snowsnow packspacks –– thethe magnitudemagnitude andand raterate ofof waterwater lostlost toto thethe atmosphereatmosphere byby sublimationsublimation –– thethe timing,timing, rate,rate, andand magnitudemagnitude ofof snowsnow meltmelt –– thethe fatefate ofof meltmelt waterwater OverviewOverview •• SnowSnow GeographyGeography •• SnowSnow MetamorphismMetamorphism •• TheThe mountainmountain snowpacksnowpack •• SnowSnow energyenergy exchangesexchanges •• SnowSnow measurementsmeasurements –– GroundGround –– AirAir andand spacespace borneborne SnowSnow GeographyGeography Precipitation,Precipitation, Distribution,Distribution, RedistributionRedistribution WhatWhat factorsfactors controlcontrol thethe distributiondistribution ofof snowsnow extentextent andand snowsnow waterwater equivalentequivalent (SWE)?(SWE)? ItIt dependsdepends onon thethe scale.scale. ••ContinentalContinental ScaleScale ••MesoscaleMesoscale ••BasinBasin ScaleScale SnowSnow CoverCover DistributionDistribution Three Spatial Scales Macroscale • Areas up to 106 km2. • Characteristic Distances of 10-1000 km. • Dynamic meteorological effects are important. Mesoscale • Characteristic Distances of 100 m to 10 km. • Redistribution of snow along relief features due to wind. • Deposition and accumulation of snow may be related to terrain variables and to vegetation cover. Microscale • Characteristic Distances of 10 to 100 m. • Differences in accumulation result from variations in air flow patterns and transport. ContinentalContinental ScaleScale • Latitude • Elevation • Orography MesoscaleMesoscale/Regional/Regional • Synoptic scale storms Toulomne • Elevation Mono lake • Topographic configuration • Topographic configuration Merced Owens Valley Central Valley 17 BasinBasin ScaleScale (our(our mainmain interest)interest) •Wind Redistribution •Avalanche Redistribution •Terrain Configuration •Vegetation Properties MountainMountain SnowpackSnowpack CharacteristicsCharacteristics •• WindWind distributiondistribution •• AvalancheAvalanche redistributionredistribution MicroMicro scalescale Open Environments – Over highly exposed terrain, the effects of meso- and micro-scale differences in vegetation and terrain features may produce wide variations in accumulation patterns. JetJet StreamStream PolarPolar andand SubtropicalSubtropical •• BoundaryBoundary betweenbetween differingdiffering airair massesmasses •• SteersSteers StormsStorms •• BirthplaceBirthplace ofof stormsstorms systemssystems StormStorm TracksTracks •• MostMost commoncommon birthbirth place:place: GulfGulf ofof AlaskaAlaska •• ClippersClippers •• PineapplePineapple ExpressExpress •• NevadaNevada oror TonopahTonopah LowsLows •• ColoradoColorado LowLow LIFTINGLIFTING PROCESSESPROCESSES •• CyclonicCyclonic LiftingLifting •• FrontalFrontal LiftingLifting •• OrographicOrographic LiftingLifting •• JetJet SupportSupport CyclonicCyclonic LiftingLifting AroundAround aa LowLow \ FrontalFrontal LiftingLifting OrographicOrographic LiftingLifting • Air is forced up over the Sierra’s • Expansional cooling leads to condensation and precipitation on the windward side • Compressional heating and evaporation on the lee side • Rain Shadow MostMost favorablefavorable alignmentsalignments forfor OrographicOrographic enhancementsenhancements… •• PerpendicularPerpendicular •• ConcaveConcave AnatomyAnatomy ofof aa SnowSnow CrystalCrystal Dendrite Sectored Plate Dendritic Needle Prism Sectored Plate (Column) NorthernNorthern CaliforniaCalifornia WeatherWeather PacificPacific “High”“High” –– DeclinesDeclines inin winterwinter andand letslets stormsstorms throughthrough –– IncreasesIncreases inin summersummer && keepskeeps stormsstorms outout –– AirAir warmedwarmed atat equatorequator risesrises && headsheads forfor Arctic.Arctic. SomeSome ofof itit cools/sinks.cools/sinks. ThisThis “mountain”“mountain” ofof coolcool airair weighsweighs heavyheavy (high(high pressure)pressure) onon surfacesurface –– WinterWinter –– GulfGulf ofof AlaskaAlaska && SouthernSouthern CaliforniaCalifornia highhigh (offshore)(offshore) NorthernNorthern CaliforniaCalifornia WeatherWeather SierraSierra isis aa maritimemaritime climateclimate –– StormsStorms holdhold moremore moisture.moisture. RockiesRockies havehave lessless waterwater contentcontent soso snowsnow isis drierdrier Ocean Coast Range Sierra Rockies ContinentalContinental SnowpackSnowpack •• ShallowShallow snowpacksnowpack •• LowLow densitydensity (( 7070 kg/mkg/m3 newnew snowsnow density)density) •• LowLow airair temperaturestemperatures ((--7.37.3 oCC)) •• DepthDepth hoarhoar –– hidden,hidden, persistentpersistent instabilitiesinstabilities •• HighHigh temperature/vaportemperature/vapor gradientgradient (( >> 1010 oCC/m,/m, atat timestimes >>>> 1010 oCC/m)/m) •• ExampleExample ranges:ranges: RockyRocky MountainsMountains (Colorado,(Colorado, NewNew Mexico,Mexico, Montana,Montana, Wyoming,Wyoming, Canada).Canada). MaritimeMaritime SnowpacksSnowpacks •• DeepDeep snowpacksnowpack •• HighHigh densitydensity (120(120 kg/mkg/m3 newnew snowsnow density)density) •• ModerateModerate airair temperaturestemperatures ((--1.31.3 oCC)) •• LowLow temperature/vaportemperature/vapor pressurepressure gradientgradient (<(< 1010 oCC/m)/m) •• AvalanchesAvalanches duringduring oror immediatelyimmediately afterafter stormsstorms •• ExampleExample ranges:ranges: SierraSierra Nevada,Nevada, Cascades,Cascades, CoastCoast RangeRange (B.C.)(B.C.) TransitionalTransitional ClimateClimate TransitionalTransitional snowpackssnowpacks----likelike thatthat ofof Utah'sUtah's WasatchWasatch MountainsMountains----exhibitexhibit characteristicscharacteristics ofof bothboth MaritimeMaritime andand ContinentalContinental snowpacks.snowpacks. ContinentalContinental MaritimeMaritime Data source: Western Regional Climate Center SnowSnow metamorphismmetamorphism 1.1. DefinitionsDefinitions 2.2. InitialInitial metamorphismmetamorphism 3.3. EquilibriumEquilibrium processesprocesses 4.4. KineticKinetic processesprocesses 5.5. Melt/FreezeMelt/Freeze 6.6. MountainMountain snowpacksnowpack characteristicscharacteristics DensityDensity –– MassMass perper volume,volume, usuallyusually specifiedspecified inin kilogramkilogram perper cubiccubic metermeter oror asas percentpercent water.water. –– IndicatorIndicator ofof strengthstrength andand thethe formationformation ofof aa slab.slab. TemperatureTemperature GradientGradient –– TemperatureTemperature variationsvariations
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