F. Valente

Modelling interception loss for two sparse eucalypt and pine forests in central Portugal using reformulated Rutter and Gash analytical models

Abstract Gross rainfall, throughfall and stemflow were measured in Eucalyptus globulus Labill. and Pinus pinaster Ait. stands in central Portugal over two and a half years (from January 1992 to July 1994). The results show that the interception loss is higher in the pine stand (17% of gross rainfall) than in the eucalypt stand (11% of gross rainfall). Interception loss was also simulated by the Rutter model and Gashs original analytical model, but both models overestimated the interception loss from these Mediterranean sparse forests by 29–44%. To improve the description of the rainfall interception from sparse forests, the Rutter model was reformulated. This new version of the Rutter model and a previously reformulated version of Gashs analytical model greatly improved the accuracy of the simulation for both forests, resulting in estimates of the interception loss within 3% of the measured values.

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

Abstract 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.