Evaporation of Intercepted Rainfall

Abstract When rain falls on to a vegetated surface (gross rainfall), a part is intercepted by the canopy and evaporated directly back into the atmosphere (interception loss). The remainder of the rainfall reaches the ground (net rainfall) either through gaps and by dripping from the canopy (throughfall), or by running down the main stem (stemflow). The canopy storage capacity is the minimum amount of water necessary to completely saturate the canopy surface. Interception loss is conventionally measured as the difference between the incident gross rainfall, and the sum of throughfall and stemflow. It is usually a significant component of the overall evaporation and may play an important role in watershed water balance. The total amount of interception loss depends on the rate of evaporation from the wet canopy, the canopy storage capacity, and the distribution and intensity of rainfall. Interception loss is particularly high in forests due to their high aerodynamic roughnesses. Available models range from empirical relationships to physically based conceptual models. Within the latter, the Rutter‐type models are those that have been taken up as the more generally applicable technique. Most of the models rely on the use of the Penman–Monteith equation to estimate the evaporation rate. Current research is largely directed at modeling in horizontally heterogeneous vegetation, where the Penman–Monteith equation may not be valid.