To what extent can the vegetation boundary conditions be modified?
The GISS GCM includes eight vegetation “types”: Desert, Rainforest, Woodland, Evergreen Forest, Deciduous Forest, Grassland, Shrubs and Tundra. Each type is defined by the physical characteristics of Visible Albedo, NIR Albedo, Water Field Capacity, Roughness Length, and Snow Masking Depth. Despite the simple sounding names of the vegetation types, each type is actually a compilation of many tens of other vegetation categories and is assigned at a 1 x 1 degree resolution. The GCM uses a “fractional” scheme in which each 8 x 10 degree grid cell in the model is assigned a fraction of each vegetation type, based on the corresponding 1 x 1 cells. Thus, every grid cell in the GCM is made up of multiple vegetation types. We can change certain grid cells to be all one type, or we can change the physical characteristics of any vegetation type, but we cannot change just one type of vegetation over just one region. For example, the Desert characteristics are adjusted, then all geographic locatio
