Estimates and measurements of evaporation from wet, sparse pine forest in Portugal

Measurements of evaporation were made from a wet, sparse pine forest using the eddy correlation/energy balance method in saturated canopy conditions. The measurements were compared with the estimates of evaporation made using the Penman-Monteith equation in both the original and a sparse forest version of the Rutter model, where the evaporation is reduced in proportion to the canopy cover. The use of different formulations of the aerodynamic conductance was also investigated. The best agreement was found when the aerodynamic conductance for vapour flux was set equal to the measured conductance to momentum flux and then used in the sparse forest version of the Rutter model. This good agreement was a result of an accurate prediction of the aerodynamic conductance to vapour flux. There was poor agreement with observations when the estimated aerodynamic conductance for vapour included an empirical relationship between the roughness lengths for heat/ vapour and momentum derived previously for dry conditions. (C) 1999 Elsevier Science B.V. All rights reserved.