Application of a six-layer SVAT model for simulation of evapotranspiration and water uptake in a spruce forest

The One-Dimensional non-steady-state Six-Layer SVAT model (SLODSVAT) was applied to a quasihomogeneous stand of spruce trees (Picea abies [L.] Karst) in the Selling hills (Germany) in order to describe the water transport from the soil into the atmosphere through the roots-stem-shoots-needles system of the trees and to predict the possible response to changes of soil water conditions on transpiration rate of the forest. The modelled water uptake and evapotranspiration rates were compared with long-term sap flow, eddy correlation and gradient flux measurements for a one-week test period (01-08.07.1995) which provided a variety of weather conditions including clear as well as partly cloudy and rainy days. Moreover, for this period the sensitivity of response of the transpiration rate and water uptake to changes of environmental conditions is estimated. The results show, that the SLODSVAT can describe and simulate the short-term variability of water uptake by the roots and evapotranspiration in the spruce forest adequately under different environmental conditions. For the selected period the SLODSVAT explained about 94% of the variation of water uptake (r(2)=0.940), and 88% and 78% of variation of evapotranspiration measured by Bowen ratio - energy balance (r(2)=0.881) and eddy correlation (r(2)=0.785) methods, respectively. Thus, these results give evidence that it is possible to estimate and predict evapotranspiration and transpiration rates for spruce forest ecosystems in the stand-scale during one vegetation period if appropriate input parameters for the soil and canopy structure and the atmospheric conditions are available. (C) 1997 Elsevier Science Ltd.