Radiation Schemes in Biophysical Models: Big Leaf vs. 2-Leaf Submodel in the Simple Biosphere Model (SiB) Ian Baker ChEAS Annual Meeting Kemp Research Station 01 June 2005

MOTIVATION SiB2/SiB3 Comparison Latent heat flux for both versions looks good NEE looks better in SiB3 H is worse in SiB3! new water stress Is radiative scheme the problem? Wetlands?

SiB: Big Leaf Radiation

Linkage: Photosynthesis and leaf energetics coupled through stomatal resistance Inconsistent: Diffuse light neglected in photosynthesis is accounted for in leaf energetics MY PET THEORY: In wet, dense canopy environments, potential for leaf heating with insufficient transpiration (i.e. photosynthesis) to cool leaf

2-Leaf Radiation

Does it work? Sure looks like it H much lower in summer months LE increases Must make adjustments to keep photosynthesis and respiration reasonable

Bowen Ratio 2-leaf Bowen Ratio lower than Big-leaf BR in summer Both models have trouble in spring, 2L worse

Adjustments to Photosynthesis Two ‘knobs’ Vm calculation (sun and shade leaves) de Pury & Farquhar Wang & Leuning Vmax value From tables Adjusted (Collatz)

Ongoing Issues Conservation of energy and water: small amounts of imbalance exist. Re-deriving equations will remedy this Parameters (not just VMAX0) have been developed for big-leaf model-are they incorrect for two-leaf model? Two-leaf SiB looks good at WLEF; How about other sites (grassland, tropics)?

Some References Dai, Y., R.E. Dickinson, Y.-P. Wang, 1998: A Two-Leaf Model for Canopy Temperature, Photosynthesis, and Stomatal Conductance. Journal of Climate, 17, De Pury, D.G.G., Farquhar, G.D, 1997: Simple Scaling of Photosynthesis from Leaves to Canopies without the errors of Big-Leaf Models. Plant, Cell, and Environment, 20, Dickinson, R.E., 1983: Land Surface Processes and Climate-Surface Albedos and Energy Balance. Advances in Geophysics, 25,305. Sellers, P.J., 1985: Canopy Reflectance, Photosynthesis and Transpiration. International Journal of Remote Sensing, 6(8), Sellers, P.J., J.A. Berry, G.J. Collatz, C.B. Field, F.G. Hall, 1992: Canopy Reflectance, Photosynthesis, and Transpiration. III. A Reanalysis Using Improved Leaf Models and a New Canopy Integration Scheme. Remote Sensing and Environment, 42: Wang, Y.-P., Leuning, R., 1998: A Two-Leaf Model for Canopy Conductance, Photosynthesis and Partitioning of Available Energy I: Model Description and Comparison with a Multi-Layered Model. Agricultural and Forest Meteorology, 91,