Ane \ v paradigm of forest canopy interception science : the implication of a huge amount of evaporation during rainfall

Canopy interception includes some enigmatic problems. Firstly, evaporation rate is proportional to the rainfall intensity. Secondly, the heat budget model underestimates the measured canopy interception at some sites but the Gash models do not, though both types of models are physically based. Thirdly, though high evaporation rate during rainfall, e.g. ~ 10 mm h-1, was observed, the source of latent heat of vaporization and efficient water vapor transfer mechanism during rainfall remain unsolved. The first problem, the dependence of canopy interception on rainfall intensity, DOCIORI, cannot be explained by the conventional heat budget model, since rainfall intensity is not included as a parameter. To elucidate the phenomenon, the idea of splash droplet evaporation, SDE, was proposed. As the raindrop size and the number of raindrops per unit volume increase with the rainfall intensity, so does the number of splash droplets produced by the raindrops hitting on the canopy. Splash droplets evaporate efficiently due to large combined surface area. The DOCIORI was pointed out in the Japanese sites for the first time in the 1980s, but has not been known worldwide until recently. In this chapter it is shown that the DOCIORI occurs at sites other than in Japan using literature data in which authors did not notice the phenomenon. The second problem is also understandable by SDE; the heat budget model considers evaporation from canopy surface only but actual evaporation occurs from the surface of splash droplets as well. This overlook leads to underestimation of the heat budget model especially where rainfall intensity is sufficiently high, while estimation by the Gash models reproduces the measurement fairly well, because they include SDE implicitly. The tllird problem concerns not only forest hydrology but also atmospheric sciences, and is explainable at least qualitatively by the innovative idea of evaporative force proposed recently, which is an unnoticed basic principle in meteorology.