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Surface Water Balance (1)

Surface Water Balance (1). Review of last lecture: Surface energy balance. Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface conduction. SWdn =Scos . SWup =SWdn .

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Surface Water Balance (1)

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  1. Surface Water Balance (1)

  2. Review of last lecture: Surface energy balance Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface conduction SWdn =Scos SWup =SWdn  LWdn =Tair4 LWup=Ts4 LH=CdLV(qsurface- qair) SH=CdCpV(Tsurface- Tair)  dT/dt Fc = -  dT/dz • 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 SHand 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

  3. The global water cycle

  4. Components 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)

  5. Atmosphere: water vapor

  6. Atmosphere: Precipitation Inter-tropical convergence zone (ITCZ) Strong rainfall (heating) Weak rainfall GPCP Annual Mean Precipitation for 1979-2005 (mm/day)

  7. Land snow/Ice cover provide a reservoir

  8. Flow of >1000 rivers on the seven continents Mississippi river Amazon river Yangtze river

  9. Land: Soil moisture

  10. Flow of ocean currents

  11. A significant fraction of the human body is water (~75%) About every 16 days nearly 100% of the water in a human body is exchanged. The remaining: fat, protein, carbonhydrate, other solids

  12. 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

  13. Surface water balance The changing rate of soil moisture S dS/dt = P - E - Rs - Rg + I Precipitation (P) Evaportranspiration (E) Irrigation (I) Runoff (Rs) dS/dt Infiltration (Rg)

  14. Evaportranspiration • Is equivalent to latent heat flux • Has four components: E = Eb + Ei + Es + TR Evaporation from inception storage (Ei) Transpiration (TR) Evaporation from bare soil (Eb) Snow sublimation (Es)

  15. Evaportranpiration: Penman-Monteith equation where Rn is the net radiation, G is the soil heat flux, (es - ea) represents the vapour pressure deficit of the air, ra is the mean air density at constant pressure, cp is the specific heat of the air, D represents the slope of the saturation vapour pressure temperature relationship, g is the psychrometric constant, and rs and ra are the (bulk) surface and aerodynamic resistances.

  16. Soil moisture • Typically expressed as ‘volumetric soil water content’ S = Vwater / Vsoil • Increases with depth • Complicated to measure Root zone Intermediate zone Ground water

  17. Soil moisure regimes

  18. US Soil moisture map

  19. 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.

  20. PSDI for US in August 2012

  21. Glacier mass balance • 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.

  22. Summary:Components 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)

  23. Surface water balance The changing rate of soil moisture S dS/dt = P - E - Rs - Rg + I Evaportranspiration (E=Eb+Ei+Es+TR) Penman-Monteith eq Precipitation (P) Irrigation (I) Runoff (Rs) dS/dt (PDSI, desertification) Infiltration (Rg Darcy’s law)

  24. Works cited • http://ffden-2.phys.uaf.edu/212_spring2011.web.dir/Jocelyn_Simpson/Slide3.htm

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