Representation of the Canopy Conductance in Modeling the Surface Energy Budget for Low Vegetation

Abstract

In this study, the authors develop and validate an approach to calculate a canopy conductance that can successfully be implemented in an atmospheric model. The approach is based on plant physiology approaches that have developed recently. However, it includes a new analytic formulation to scale the conductance up from leaf to canopy. Furthermore, a new expression that accounts for the effect of soil moisture on the canopy conductance is proposed. The parameters are not optimized locally; rather, values are assigned to them as a function of vegetation type. This approach is validated for three experimental sites: the First International Satellite Land Surface Climatology Project Field Experiment (FIFE)?Kansas area, the Hydrological Atmospheric Pilot Experiment?Modélisation du Bilan Hydrique (HAPEX?MOBILHY) site, and the Cabauw area. The vegetation at these sites is representative for large areas with low vegetation in the world. The results of the plant physiological approach are based on a distinction in C3 and C4 plant types, and these results are found to be better (FIFE?Kansas) and more consistent (HAPEX?MOBILHY) than estimates obtained by a traditional Jarvis?Stewart approach. The parameters of the latter are also obtained from a vegetation classification. For the Cabauw area, both approaches perform comparably. Furthermore, the new soil moisture content response function is found with work well, as compared with previous formulations.