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. Savanna Woodland adjacent to Grassland
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 5

6. On Annual Time Scale, Forest ET > Grass ET
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
5. Mean Potential Temperature differences are relatively small (0.84 C; grass: vs savanna: 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 vs Savanna:
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, Ra and albedo….!!
And temperatures are about equal when albedo of the grass is 0.25
Summer Conditions

14. Tsfc can vary by 10 C by changing Ra and Rs
Mean Tsfc field as a function of Ra and Rs for a range of albedos

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

16. Tair can vary by 3 C by changing albedo and Rs
Diurnal pattern in Rg, sinusoidal and pbl model in time with variation in parameters

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

21. 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

23. Feedbacks with Surface Temperature
ESPM 129 Biometeorology