Evapotranspiration in several woody species of Central Portugal

Abstract : Evapotranspiration was followed in several stands in central Portugal, with the aim of quantifying the water consumption and determining some parameters used in evapotranspiration modelling, in respect to some of the most important woody species in this region. Three stands were used: an irrigated peach orchard, a Eucalyptus globulus plantation and a Pinus pinaster forest. The experiments were conducted during spring and summer 1994. Evapotranspiration was measured using the eddy covariance method in the pine and peach stands for limited periods, and the results are compared with the sum of transpiration (sap-flow method) and soil evaporation. Since the results could be taken as equivalent, sap-flow measurements were used to follow transpiration during longer periods in all stands. The relative contribution of sensible (H) and latent (LE) fluxes in relation to net radiation (Rn) is described, as well as the relative average contributions of transpiration (T) and soil evaporation (Es) to total evapotranspiration. The seasonal variations of T+Es over ETo, stomatal conductance (g s) and Omega coefficient (Omega) are presented. The decrease of (T+Es)/ETo follows a significant decrease in g s during drought periods. According to the very low values of Omega (on average < 0.13, in all stands), g s can not be neglected in ET modelling.