Evaporation from rain-wetted forest in relation to canopy wetness, canopy cover, and net radiation

Evaporation from wet canopies is commonly calculated using E-PM, the Penman-Monteith equation with zero surface resistance. However, several observations show a lower evaporation from rain-wetted forest. Possible causes for the difference between E-PM and experiments are evaluated to provide rules for the simulation of rainfall interception by forest canopies. The evaluation is executed using a micrometeorological model with a detailed representation of the forest canopy. Simulated results are compared with experimental results. In spite of theoretical reservations the evaporation of completely wet forest appears to agree with E-PM. Evaporation from wet forest appears mainly dependent on net radiation. Rainfall interception is related to evaporation from the canopy. Evaporation from the canopy appears proportional with the square root of canopy cover and sensitive to canopy wetness. An accurate estimate of canopy wetness is needed to use E-PM for the calculation of evaporation from rain-wetted forest.