A Revised Land Surface Parameterization (SiB2) for Atmospheric GCMS. Part I: Model Formulation

Abstract

The formulation of a revised land surface parameterization for use within atmospheric general circulation models (GCMs) is presented. The model (SiB2) incorporates several significant improvements over the first version of the Simple Biosphere model (SiB) described in Sellers et al. The improvements can be summarized as follows: (i) incorporation of a realistic canopy photosynthesis?conductance model to describe the simultaneous transfer of CO2 and water vapor into and out of the vegetation, respectively; (ii) use of satellite data, as described in a companion paper, Part II, to describe the vegetation phonology; (iii) modification of the hydrological submodel to give better descriptions of baseflows and a more reliable calculation of interlayer exchanges within the soil profile; (iv) incorporation of a ?patchy? snowmelt treatment, which prevents rapid thermal and surface reflectance transitions when the area-averaged snow cover is low and decreasing. To accommodate the changes in (i) and (ii) above, the original two-layer vegetation canopy structure of SiB2 has been reduced to a single layer in SiB2. The use of satellite data in SiB2 and the performance of SiB2 when coupled to a GCM are described in the two companion papers, Part II and III.