THE CONCEPT OF CANOPY RESISTANCE - HISTORICAL SURVEY AND COMPARISON OF DIFFERENT APPROACHES

An historical account concerning the evolution of the concept of canopy resistance over the last 40 years is presented, from the classical Penman-Monteith equation, which is based on a single-layer approach, up to the generalized combination equation derived by Lhomme using a multi-layer approach. The different procedures for calculating the bulk aerodynamic and surface resistances of a plant canopy are given. Using a numerical simulation, the bulk canopy resistances calculated with the multi-layer approach are analysed and compared with those of the classical single-layer approach, in order to determine under which conditions the classical Penman-Monteith equation can provide a good estimate of the evapotranspiration rate of a plant canopy.