Does interception evaporation occur from both sides of leaves at the wet Japanese cypress canopy during and after rainfall?

The interception by the lower (abaxial) side of needle leaves not only contributes to the forest evapotranspiration but will also cause a diffusion barrier of CO2 over the stomata and depresses the plant gas exchange. This study combined the eddy covariance (EC) technique and leaf wetness measurement with a soil–vegetation–atmosphere transfer (SVAT) multilayer model to examine the occurrence of interception evaporation from both sides of leaves at a Japanese cypress forest canopy relating to rainfall intensity and different wetting periods. We compared the measured latent heat flux (λE) with the simulated wet canopy λE with two models that interception evaporation only happens from the upper (adaxial) side of leaves and both sides of leaves. Both models showed a low λE during the rainfall as the EC data did. The simulated λE at the wet period after rainfall indicates that the interception evaporation from both sides of leaves is more likely to happen after heavy rainfall (>15 mm/12 h). However, for the most frequent small rainfall events (0–5 mm/12 h) at this site, interception evaporation is more likely to occur only from the adaxial side than both sides, which helps the wet leaves to maintain stomata opening and process CO2 uptake after rainfall.