Modeling energy fluxes from sparse canopies and understorys

Land surfaces are an assemblage of component surface types, for instance ov erstory vegetation species, understory vegetation species, and bare soil. O ften two or more surface types absorb a significant fraction of the availab le energy to the land surface as a whole. In these cases the interaction of fluxes from the component surfaces may be important to the total land surf ace energy balance. We compare three models of land surface energy balance: a Penman-Monteith model; a model with two component surfaces that don't in teract (patch model); and a model with interacting component surfaces (Shut tleworth-Wallace model). Data from six published studies are used to invest igate which models best represent a particular land surface taking account of water supply to the component surfaces and overstory canopy architecture . Flux interaction between component surfaces was only found to be importan t when there was a large difference between the surface resistances (i.e., water availability to the surfaces). Also, all three models were found to e stimate the same land surface energy fluxes (to within 50 W m(-2)) when bot h surface resistances were >300 s m(-1). The ratio of (aerodynamic resistan ce between the canopy air space and the reference height) to (mean componen t surface boundary layer resistance) was useful for indicating the level of interaction between component surfaces.