Aggregation of Wet and Dry Land Surfaces in Interception Schemes for General Circulation Models

Abstract

This paper investigates the parameterization of rainfall interception by a vegetation canopy in GCMS. Recent land surface schemes have introduced canopy water balance equations, which include sub-grid scale rainfall variability. However, current models do not distinguish between wet and dry areas when solving the set of energy balance equations. An alternative method is set out here that solves one set of surface flux equations for the wet area and one for the dry area. The approximation of using a single surface temperature to determine the surface fluxes is shown to overestimate the wet canopy evaporation from a forest by typically 30%. When implemented in the single column version of the U.K. Meteorological Office GCM, this excessive evaporation leads to significant overprediction of modeled interception loss from Amazonian rain forest.