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 g_c. Traditionally, g_c 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 g_c is developped which relates g_c to the carbondioxyde flux density obtained using a plant physiological model (Jacobs, 1994). This approach is usually referred to as an A-g_c 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-g_c perform well. However, the parameters of the A-g_c model can be estimated a priori, whereas the coefficients of the Jarvis' functions have to optimised locally. To estimate the parameters of the A-g_c 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-g_c model.