Abstract:
Correctly modelling the Surface Energy Budget for vegetated surfaces depends heavily on obtaining good estimates for the canopy conductance to latent heat flux density gc. Traditionally, gc is related to the environmental variables evaluated at the reference height according to empirical functions given originally by Jarvis (1976). Recently, a method to obtain gc is developped which relates gc to the carbondioxyde flux density obtained using a plant physiological model (Jacobs, 1994). This approach is usually referred to as an A-gc model. Both methods are evaluated and compared with output from a reference model and measurements of the surface energy balance flux densities. It appears that both the Jarvis' functions approach and A-gc perform well. However, the parameters of the A-gc model can be estimated a priori, whereas the coefficients of the Jarvis' functions have to optimised locally. To estimate the parameters of the A-gc model a distinction between C3 and C4 types of plants already leads to good simulations of the surface balance flux densities. Since a distinction in biomes is possible, global data sets can be more easily obtained for an A-gc model.
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