Mapping surface-cover parameters using aggregation rules and remotely sensed cover classes

A coupled model, which combines the Biosphere-Atmosphere Transfer Scheme (BATS) with an advanced atmospheric boundary-layer model, is used to validate hypothetical aggregation rules for BATS-specific surface-cover parameters. The model is initialized and tested with observations from the Anglo-Brazilian Amazonian Climate Observational Study and is used to simulate surface fluxes for rain forest and pasture mixes at a site near Manaus in Brazil. The aggregation rules are shown to estimate parameters which give area-average surface fluxes similar to those calculated, with explicit representation of forest and pasture patches for a range of meteorological and surface conditions relevant to this site, but the agreement deteriorates somewhat when there are large patch-to-patch differences in soil moisture. The aggregation rules, validated as above, are then applied to a remotely sensed 1 km land-cover data set to obtain grid-average values of BATS vegetation parameters for 2.8° x 2.8° and 1° x 1° grids within the conterminous United States. There are significant differences in key vegetation parameters (aerodynamic roughness length, albedo, leaf-area index, and stomatal resistance) when aggregate parameters are compared with parameters for the single, dominant cover within the grid. However, the surface energy fluxes calculated by stand-alone BATS with the 2-year forcing data from the International Satellite Land Surface Climatology Programme CD-ROM are reasonably similar using aggregate-vegetation parameters and dominant-cover parameters, but there are some significant differences, particularly in the western USA.