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Dennis Baldocchi University of California, Berkeley NCEAS Workshop, Santa Barbara 2009

Land surface - boundary layer interactions . Dennis Baldocchi University of California, Berkeley NCEAS Workshop, Santa Barbara 2009. Case Study: Energetics of a Grassland and Oak Savanna Measurements and Model.

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Dennis Baldocchi University of California, Berkeley NCEAS Workshop, Santa Barbara 2009

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  1. Land surface - boundary layer interactions Dennis Baldocchi University of California, Berkeley NCEAS Workshop, Santa Barbara 2009

  2. Case Study: Energetics of a Grassland and Oak Savanna Measurements and Model

  3. From a CO2 perspective, the oak woodland is a Greater C sink than the Annual Grassland

  4. Case Study: Savanna Woodland adjacent to Grassland • Savanna absorbs much more Radiation (3.18 GJ m-2 y-1) than • the Grassland (2.28 GJ m-2 y-1) ; DRn: 28.4 W m-2

  5. Landscape Differences On Short Time Scales, Grass ET > Forest ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

  6. Role of Land Use on ET: On Annual Time Scale, Forest ET > Grass ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, 2008

  7. 4a. U* of tall, rough Savanna > short, smooth Grassland 4b. Savanna injects more Sensible Heat into the atmosphere because it has more Available Energy and it is Aerodynamically Rougher

  8. 5. Mean Potential Temperature differences are relatively small (0.84 C; grass: 290.72 vs savanna: 291.56 K); despite large differences in Energy Fluxes--albeit the Darker vegetation is Warmer Compare to Greenhouse Sensitivity ~2-4 K/(4 W m-2)

  9. Conceptual Diagram of PBL Interactions H and LE: Analytical/Quadratic version of Penman-Monteith Equation

  10. The Energetics of afforestation/deforestation is complicated • Forests have a low albedo, are darker and absorb more energy • But, Ironically the darker forest maybe cooler (Tsfc) than a bright grassland due to evaporative cooling

  11. Forests Transpire effectively, causing evaporative cooling, which in humid regions may form clouds and reduce planetary albedo

  12. Theoretical Difference in Air Temperature: Grass vsSavanna: Grass Tair is much cooler if we only consider albedo Summer Conditions

  13. And Smaller Temperature Difference, like field measurements, if we consider PBL, Rc, Raand albedo….!! Summer Conditions

  14. Tsfc can vary by 10 C by changing Ra and Rs

  15. Tsfc can vary by 10 C by changing albedo and Rs

  16. Tair can vary by 3 C by changing albedo and Rs

  17. Tair can vary by 3 C by changing Ra and Rs

  18. Rnet can by 100 W m-2 by changing albedo and Rs

  19. Rnet can by 30 W m-2 by changing Ra and Rs

  20. Conclusions • To understand the role of vegetation on climate we must consider more that C sink and Albedo! • Tair =f(PBL..f(H)..f(Rnet, LE, Tsfc, Gstor)..f(a, Rc, Ra)) • We must consider all the ecosystems services • Water yield, habitat, grazing, recreation • ‘We must not blame the forests for climate change if we can improve energy efficiency and reduce carbon emissions’ • Sebastiaan Luyssaert

  21. Feedbacks with Surface Temperature ESPM 129 Biometeorology

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