Lecture 2: Biophysical interactions between land and atmosphere

1. Lecture 2: Biophysical interactions between land and atmosphere Elena Shevliakova & Chip Levy

2. Energy Flows in the Atmosphere Faq 1.1 from IPCC (2007)

3. Generalized scope of interactions time-scale GB Bonan 2002, Ecological Climatology

4. Constraints of Climate on Plants • Sunlight – Available sunlight drives photosynthesis. – ~1.4 g dry matter is produced for 1MJ of intercepted sunlight (2.5% efficiency). – Heats surface and evaporates Water • Water – Hydrates cells – Causes tugor for growth and cell expansion – Transfers nutrients – Water vapor is lost as stomates open to acquire CO2 • Temperature – Regulates rates of biochemical and enzymatic reactions – Determines if water is gas, liquid or solid

5. Land cover effect on climate • Radiation • Surface albedo • Surface temperature and emissivity • Turbulent fluxes • Roughness • Stomatal conductance, Leaf area index (LAI) • Available moisture in soil and interception storage

6. Land Surface-Atmosphere Coupling *for natural fires and re-growth in boreal region.

7. Surface Energy Balance • The land surface on average is heated by net radiation balanced by exchanges with the atmosphere of sensible and latent heat • Rad_net = ShortWave_net + LongWave_net • Sensible heat [SH] is the energy carried by the atmosphere in its temperature • Latent heat [LH]is the energy lost from the surface by evaporation of surface water • The latent heat of the water vapor is converted to sensible heat in the atmosphere through vapor condensation • The condensed water is returned to the surface through precipitation.

8. Major Radiation Components • Absorbed • Reflected • Transmitted

9. Radiative Properties of the Atmosphere, Leaves and Surface • Conservation of energy: radiation at a given wavelength is either: • reflected — property of surface or medium is called reflectance or albedo (0-1) • absorbed — property is absorptance or emissivity(0-1) • transmitted — property is transmittance (0-1) reflectance + absorptance + transmittance = 1for a surface, transmittance = 0

10. General Surface Reflectance Curves from Klein, Hall and Riggs, 1998: Hydrological Processes, 12, 1723 - 1744 with sources from Clark et al. (1993); Salisbury and D'Aria (1992, 1994); Salisbury et al. (1994)

11. MODIS Broadband Albedo, 10/1986

12. Snow Albedo Feedback NH snow cover retreats rapidly as radiation and T increase Surface albedo is decreased and absorbed radiation is increased => enhanced warming Hall and Qu, 2005

13. Pitman 2003

14. GLDAS

15. LAI Biophysical Interactions

16. Surface Roughness Length

17. Roughness Length Interaction with Biophysics

18. thousands of km3 per year Image adapted from an illustration which originally appeared in Scientific American (September 1989, p. 82). http://www.globalchange.umich.edu/globalchange1/current/labs/water_cycle/water_cycle.html

19. Hydrological cycle and Climate Climate dynamics and physics depend on exchange of moisture between atmosphere, land and ocean • Water vapor acts as a greenhouse gas and nearly doubles effects of greenhouse warming CO2, methane, and all other gases • ~50% of net surface cooling* results from evaporation • ~30% of thermal energy driving atmospheric circulations provided by latent heating in clouds • Clouds alter radiation budget * This is a little tricky

20. Desertification Positive Feedback (soil moisture)

22. Forests and Future Climate Change • Biophysical forest-atmosphere interactions can dampen or amplify anthropogenic climate change • Tropical forests could mitigate warming through evaporative cooling • Boreal forests could increase warming through the low albedo • The evaporative and albedo effects of temperate forests are unclear • Potential increase in forest growth and expansion will attenuate global warming through carbon sequestration

23. Bonan 2008.

24. Land-atmosphere interactions: Amazonia (Betts & Silva Dias, 2009) • Large seasonal variations are Observed in precipitation, cloud cover and radiation, but not in temperature. • Large Observed changes in land use are believed/shown to affect surface albedo and roughness, and atmospheric composition from biomass burning, • Large scale biosphere-atmosphere experiment (LBA) since the mid 1990s • long-term monitoring; • Intensive field campaigns; • data sets;

25. Land Surface-Atmosphere Coupling *for natural fires and re-growth in boreal region.

26. Land-atmosphere interactions: tropics Betts, A.K., and M.A.F. Silva Dias, 2009: Progress in understanding land-surface-atmosphere coupling over the Amazon: a review. Submitted to J. Adv. Model. Earth Syst.

27. Land-atmosphere interactions: Tropics Betts and Silvia Dias (2009) added new pathways to the Betts (1996) diagram: • Surface influence on the seasonal behavior of clouds, aerosols and precipitation; • Impact of diffuse radiation on net ecosystem exchange; • role of convection in the transport of atmospheric tracers, including CO2; • Coupling between clouds, meso-scale dynamics, and atmospheric circulation (oceans play a role).

28. I Figured Out The Next 5 Slides!

29. Comparison of measured seasonal-varying physical properties of forest and grassland in Rondonia Source: AK Betts

30. Impact of Land Use on Land Biophysical Properties and Climate Foley et al. 2005

31. Potential natural land cover distribution Tropical deforestation experiment Historical land cover change experiment Impact of Land Cover Disturbances on Climate Exp. 1 Exp. 2 Both Exp. 1 and 2 used GFDL’s AR4 Atmosphere and Land models coupled to a slab ocean.

32. Land Cover Change and Climate • Land use impacts the amount and partitioning of available energy at the earth’s surface. • Model response is dependent on weighting of various parameter changes. • In our old land model (LM2), coupled to the atmosphere model from AR4 and a slab ocean, land use changes from forest to grassland/cropland lead to: What do you think E is? Exp. 2 Findell, Kirsten L., Elena Shevliakova, P C D Milly, and Ronald J Stouffer, July 2007: Modeled impact of anthropogenic l and cover change on climate. J ournal of Climate, 20(14), doi:10.1175/JCLI4185.1.

33. Change in annual net radiation (W/m2), 1990-NatVeg Strong local response, weak remote response • Local responses to both perturbations are generally significant • Less Rnet, less evaporation, higher temperatures [95%] • Rainfall response not homogeneous (i.e. the rainfall and temperature responses are not correlated and therefore can NOT amplify each other) • Remote responses are not significant [95%] • “Extra-tropical responses are not significant in deforestation study .... full ocean model unlikely to increase extra-tropical or tropical ocean response” • Exp. 1 Findell, Kirsten L., Thomas R Knutson, and P C D Milly, 2006: Weak simulated extratropical responses • to complete tropical deforestation. Journal of Climate, 19(12), 2835-2850.

34. Alternative View

35. Changes in precipitation AGCM CGCM CGCM - AGCM Nobre et al. 2009 J. Climate

36. Summary • Land and atmosphere are linked through exchanges of energy, moisture and chemical tracers (chemical link to be discussed). • Snow/Ice-albedo feedback is a powerful regional climate feedback in most, if not all, climate models (Suki Manabe and many others) • Surface albedo (particularly snow/ice) can be a powerful climate knob (any climate model builder will tell you). • Tropics have potential to mitigate climate change through evaporative cooling but the magnitude will depend on the future land use activities. • Major changes in tropical surface properties can have significant local and regional impact. (The climate impact outside of the tropics is a very important and not yet settled issue.) • And he biophysical couplings are numerous, intertwined and not easy to unravel (this makes simplifications tricky in the scientific sense).