DERIVATION OF CANOPY RESISTANCE FOR WATER-VAPOR FLUXES OVER A SPRUCE FOREST, USING A NEW TECHNIQUE FOR THE VISCOUS SUBLAYER RESISTANCE

The paper reports on some evaporation measurements made above a spruce forest (Picea abies) during late August and the beginning of Septembe r 1991. The period was dry, and the response of the trees to this cond ition is clearly seen in the form of the diurnal course of the evapotr anspiration. The trees close their stomata to limit the water loss. Th is is also shown through a calculation of the canopy resistance to wat er vapour exchange. During periods around noon and in the afternoon th e resistance becomes very high. The calculations are carried out by us ing a novel theory for the viscous sublayer resistance to atmosphere c anopy exchange.