Toward a New Subgrid Structure of Vegetation Canopies in Land Surface Modeling

“Vegetation” is a major component in land surface models and it’s representation in sub-grid structure is a basic issue and may have large impacts on modeling results. Currently, land surface models generally use a “mosaic” approach to represent sub-grid variation in canopy structure within a given land cell in two ways: one is based on vegetation cover types (VCT) (e.g., biomes with mixed life-forms); the other uses plant functional types (PFT)—a further breakdown of VCTs into independent PFTs. Idealized experiments showed that, for a simple three dimensional (3D) canopy scenario, the VCT and PFT representations may have large discrepancies in terms of radiation transfer, resistance and surface flux calculations. The discrepancies in surface flux can be attributed to differences in the radiation absorptions and resistance values which are all due to different assumptions of canopy structures. In this study, we proposed a new sub-grid structure of vegetation canopies which is based on the VCT but with explicit representations with PFTs (not mixed life-form biomes anymore). All the PFTs with in a biome share the light and water resources, and co-exist/compete in a common environment. The canopy radiative transfer process and turbulence exchange are resolved in a 3D way. A new suite of vegetation dataset for the new sub-grid structure was developed. We applied the new sub-grid structure in the common land model (CoLM2014) and compared with the conventional VCT and PFT representations in global offline simulations. Preliminary results are shown and implications are also given.