Upload
marion-mckenzie
View
212
Download
0
Embed Size (px)
Citation preview
Surface Water BalanceSurface Water Balance
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
The global water cycleThe global water cycle
Video: Weather WetVideo: Weather Wet
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)
Atmosphere: water vaporAtmosphere: water vapor
Atmosphere: PrecipitationAtmosphere: Precipitation
GPCP Annual Mean Precipitation for 1979-2005 (mm/day)
Inter-tropical convergence zone (ITCZ)
Strong rainfall (heating)
Weak rainfall
Land snow/Ice cover provide a reservoir Land snow/Ice cover provide a reservoir
Flow of >1000 rivers on the seven continentsFlow of >1000 rivers on the seven continents
Amazon river Yangtze riverMississippi river
Land: Soil moistureLand: Soil moisture
Flow of ocean currentsFlow of ocean currents
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
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
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
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)
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.
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
Soil moisure regimesSoil moisure regimes
US Soil moisture mapUS Soil moisture map
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.
Change of PDSI in the last 100 yearsChange of PDSI in the last 100 years
PSDI for US in January 2015PSDI for US in January 2015
A different index: U.S. Drought MonitorA different index: U.S. Drought Monitor
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
Glacier mass balanceGlacier mass balance
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”.
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.
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
Glacier mass balance for the globeGlacier mass balance for the globe
Glacier mass balance for different regionsGlacier mass balance for different regions
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)
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)
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/