Surface Water Balance. Review of last lecture: Surface energy balance dT/dt SWdn =Scos SWup =SWdn ...
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Transcript of Surface Water Balance. Review of last lecture: Surface energy balance dT/dt SWdn =Scos SWup =SWdn ...
![Page 1: Surface Water Balance. Review of last lecture: Surface energy balance dT/dt SWdn =Scos SWup =SWdn LWdn = Tair 4 LWup = Ts 4 LH= C d LV(q surface.](https://reader036.fdocuments.in/reader036/viewer/2022070407/56649e425503460f94b35816/html5/thumbnails/1.jpg)
Surface Water BalanceSurface Water Balance
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Review of last lecture: Surface energy balanceReview of last lecture: Surface energy balance
dT/dt
SWdn =Scos
SWup =SWdn
LWdn =Tair4
LWup=Ts4
LH=CdLV(qsurface- qair)
SH=CdCpV(Tsurface- Tair)
Fc = - dT/dz
Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface conduction
• What is sensible heat flux? What is latent heat flux?
• Bowen ratio B= SH/LH = Cp(Tsurface - Tair) / L(qsurface - qair) provides a simple way for estimating SH and LH when the net radiative flux Fr is available LH=Fr/(B+1), SH=Fr B/(B+1)
• Factors affecting soil thermal conductivity
• Other heat sources: precipitation, biochemical, anthropogenic
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The global water cycleThe global water cycle
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Video: Weather WetVideo: Weather Wet
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Components of global water cycleComponents of global water cycle
• Atmosphere (water vapor, clouds, precipitation)• Land (soil moisture, rivers, snow, ice sheet and glaciers)• Sea ice• Ocean• Biosphere (including human beings)
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Atmosphere: water vaporAtmosphere: water vapor
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Atmosphere: PrecipitationAtmosphere: Precipitation
GPCP Annual Mean Precipitation for 1979-2005 (mm/day)
Inter-tropical convergence zone (ITCZ)
Strong rainfall (heating)
Weak rainfall
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Land snow/Ice cover provide a reservoir Land snow/Ice cover provide a reservoir
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Flow of >1000 rivers on the seven continentsFlow of >1000 rivers on the seven continents
Amazon river Yangtze riverMississippi river
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Land: Soil moistureLand: Soil moisture
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Flow of ocean currentsFlow of ocean currents
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A significant fraction of the human body is A significant fraction of the human body is water (~75%)water (~75%)
About every 16 days nearly 100% of the water in a human body is exchanged.
The remaining: fat, protein, carbonhydrate, other solids
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So the water we drink may come from …So the water we drink may come from …
Therefore we need to protect the environment because any pollution we put into the environment may someday come back into our bodies
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Surface water balanceSurface water balance
dS/dt
Precipitation (P)
Evaportranspiration (E)
Runoff (Rs)
Irrigation (I)
Infiltration (Rg)
The changing rate of soil moisture S
dS/dt = P - E - Rs - Rg + I
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Evaporation from bare soil (Eb)
EvaportranspirationEvaportranspiration• Is equivalent to latent heat flux
• Has four components: E = Eb + Ei + Es + TR
Evaporation from inception storage
(Ei)
Transpiration (TR)
Snow sublimation (Es)
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Evaportranpiration: Penman-Monteith equationEvaportranpiration: Penman-Monteith equation
where λ is latent heat of evaporation, Rn is the net radiation, G is the soil heat flux, (es - ea) represents the vapour pressure deficit of the air, a is the mean air density at constant pressure, cp is the specific heat of the air, represents the slope of the saturation vapour pressure temperature relationship, is the psychrometric constant (=66 Pa/K), and rs and ra are the (bulk) surface and aerodynamic resistances.
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Soil moistureSoil moisture• Typically expressed as ‘volumetric soil water content’
S = Vwater / Vsoil
• Increases with depth• Complicated to measure
Root zone
Intermediate zone
Ground water
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Soil moisure regimesSoil moisure regimes
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US Soil moisture mapUS Soil moisture map
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Palmer drought severity index (PDSI)Palmer drought severity index (PDSI)
• was developed by Wayne Palmer in the 1960s and uses temperature and rainfall information in a model to determine dryness of soil moisture.
• is most effective in determining long term drought (a matter of several months) and is not as good with short-term forecasts (a matter of weeks).
• It uses a 0 as normal, and drought is shown in terms of minus numbers; for example, minus 2 is moderate drought, minus 3 is severe drought, and minus 4 is extreme drought.
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Change of PDSI in the last 100 yearsChange of PDSI in the last 100 years
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PSDI for US in January 2015PSDI for US in January 2015
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A different index: U.S. Drought MonitorA different index: U.S. Drought Monitor
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Video: Crippling Drought in the Video: Crippling Drought in the Golden State: California Soul Golden State: California Soul
• https://www.youtube.com/watch?v=lmUwjk4S3gw
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Glacier mass balanceGlacier mass balance
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Structure of a glacierStructure of a glacier
• A glacier forms when the accumulation of snow and ice exceeds its overall loss of mass by ablation (sublimation and melting).
• A glacier can be divided into two zones; the zone of accumulation and the zone of ablation. They are separated by the “equilibrium line”.
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Accumulation zoneAccumulation zone
• Surface accumulation processes include snow and ice from direct precipitation, avalanches and windblown snow.
• There may be minor inputs from hoar frost (radiation frost).
• The snow and ice is then transferred downslope as the glacier flows.
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Ablation zoneAblation zone
• Surface ablation processes include surface melt, surface meltwater runoff, sublimation, avalanching and windblown snow.
• Glaciers on steep slopes may also dry calve, dropping large chunks of ice onto unwary tourists below.
• Other processes of ablation include subaqueous melting, and melting within the ice and at the ice bed
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Glacier mass balance for the globeGlacier mass balance for the globe
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Glacier mass balance for different regionsGlacier mass balance for different regions
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Summary:Summary:Components of global water cycleComponents of global water cycle
• Atmosphere (water vapor, clouds, precipitation)• Land (soil moisture, rivers, snow, ice sheet and glaciers)• Sea ice• Ocean• Biosphere (including human beings)
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Surface water balanceSurface water balance
dS/dt
Precipitation (P)
Evaportranspiration (E=Eb+Ei+Es+TR)
Penman-Monteith eq
Runoff (Rs)
Irrigation (I)
Infiltration (Rg Darcy’s law)
The changing rate of soil moisture S
dS/dt = P - E - Rs - Rg + I
(PDSI, desertification)
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Works citedWorks cited
• http://ffden-2.phys.uaf.edu/212_spring2011.web.dir/Jocelyn_Simpson/Slide3.htm
• http://www.antarcticglaciers.org/modern-glaciers/introduction-glacier-mass-balance/