A model for the water regime of a deciduous forest

The relationships between actual evapotranspiration, atmospheric conditions and soil water content in the root zone are described in a simple functional model. Some constants which are used in these relationships, but unknown for forest areas, have been estimated for a deciduous forest near Zürich in Switzerland (Brülhart, 1969). On sufficiently humid soil the evapotranspiration of this forest was more than twice as high as for agricultural crops. On the other hand in the forest the evapotranspiration reacted much more sensitively on drying of the soil. On warm summer days (evaporation of free water about 0.4–0.6 cm per day) the trees considerably reduced their water delivery to the atmosphere at soil water suctions of slightly more then 0.05 bars (Fig. 7).