A Method of Measuring the Aerodynamic Resistance to the Transport of Water Vapour from Forest Canopies

Abstract

Many models of evaporation from vegetation depend not only on meteorological parameters but also on surface parameters such as the aerodynamic and stomatal resistances to the diffusion of water vapour from the vegetation. A limitation on the use of these models has been the difficulty of measuring or estimating the resistance terms. This paper describes a method of measuring the aerodynamic resistance (ra) to the transport of water vapour from a forest canopy. By definition ra is the resistance to molecular and turbulent diffusion of water vapour between leaf surfaces and the air above the canopy at a reference height. It is given by: