A two-leaf model for canopy conductance, photosynthesis and partitioning of available energy. II. Comparison with measurements

A new two-leaf canopy model for predicting fluxes of net radiation, sensible heat, latent heat and CO2 between plant canopies and the atmosphere was tested against 228 half-hourly micrometeorological flux measurements spanning over two months during the vegetative growth of two wheat crops. During that period green area index ranged from 1.8 to 4.5 for the fertilised crop and from 1.0 to 2.7 for the control crop. Excellent agreement was obtained between simulations and measurements for fluxes of net radiation, latent heat and CO2, although sensible hear fluxes were less satisfactory, Uncertainties in estimates for fluxes of water vapour and CO2 from the underlying soil contributed to discrepancies between measurements and simulations. Modelled canopy fluxes of both CO2 and latent heat are highly sensitive to the quantum yield of photosynthesis (mu mol CO2 mol(-l) quanta). Fluxes of latent heat are more sensitive than CO2 to parameters describing stomatal function, while CO2 flux was more sensitive than transpiration to maximum carboxylation rates.The two-leaf model requires only a few parameters that may vary with plant species. It is computationally 10 times more efficient than an earlier described multilayered model and is suited for incorporation into regional- or global-scale climate models. (C) 1998 Published by Elsevier Science B.V. All rights reserved.