Modelling Evaporation from Plant Canopies

This report reviews the range of approaches currently used to model evaporati on from plant canopies. Common terminology is defined and the basic methods for calculating potential evaporation are briefly outlined. A range of techniques is then presented for deriving actual evaporation both directly and indirectly. In recognition of its extensive usage, particular attention is paid to the Penman- Monteith equation and the various methodologies for estimating its component variables are reviewed. Cases where the equation has been adapted and ex tended to simulate natural systems in a more realistic way are discussed. Building on the theoretical approach described in detail, the estimation of evaporation from real vegetation types is considered, with the representation of evaporation processes in crops, forests and high altitude grasslands taken as special cases. In conclusion , the recent growth in interest in scaling issues is shown to be highly applicable in evaporation studies and effective approaches are discussed