Implementation and evaluation of a generalized radiative transfer scheme within canopy in the soil‐vegetation‐atmosphere transfer (SVAT) model

Abstract

AbstractThe process of radiative transfer over vegetated areas has a profound impact on energy, water, and carbon balances over the terrestrial surface. In this paper, a generalized radiative transfer scheme (GRTS) within canopy is implemented in the Simplified Simple Biosphere land surface model (SSiB). The main concept and structure of GRTS and its coupling methodology to a land model are presented. Different from the two‐stream method, the GRTS takes into account the effects of complex canopy morphology and inhomogeneous optical properties of leaves on radiative transfer process within the canopy. In the offline SSiB/GRTS simulation for the period of 2001–2012, the nonuniform leaf angle distribution within canopy layers is considered in SSiB/GRTS in the areas of evergreen broadleaf trees. Compared with the SSiB/two stream method, SSiB/GRTS produces lower canopy reflectance and higher transmittance, which leads to more realistic albedo simulation. The canopy‐absorbed radiation flux in SSiB/GRTS simulation is lower than that in SSiB/two stream method simulation throughout the year in the areas of evergreen broadleaf trees. The largest difference of −18.4 W/m2 occurs in the Amazon region in the autumn. The ground‐absorbed radiation flux increases in the SSiB/GRTS simulation, especially in the spring and autumn. The largest difference in the ground‐absorbed radiation flux between SSiB/GRTS simulation and SSiB/two stream method simulation is 25.45 W/m2. In the boreal winter season, compared with the two‐stream method in the SSiB, the GRTS gives higher surface albedo in the areas with high snow cover fraction over leaf.