Coupled atmosphere-biophysics-hydrology models for environmental modeling

The formulation and implementation of LEAF-2, the Land Ecosystem-Atmosphere Feedback model, which comprises the representation of land-surface process es in the Regional Atmospheric Modeling System (RAMS), is described. LEAF-2 is a prognostic model for the temperature and water content of soil, snow cover, vegetation, and canopy air, and includes turbulent and radiative exc hanges between these components and with the atmosphere. Subdivision of a R AMS surface grid cell into multiple areas of distinct land-use types is all owed, with each subgrid area, or patch, containing its own LEAF-2 model, an d each patch interacts with the overlying atmospheric column with a weight proportional to its fractional area in the grid cell. A description is also given of TOPMODEL, a land hydrology model that represents surface and subs urface downslope lateral transport of groundwater. Details of the incorpora tion of a modified form of TOPMODEL into LEAF-2 are presented. Sensitivity tests of the coupled system are presented that demonstrate the potential im portance of the patch representation and of lateral water transport in idea lized model simulations. Independent studies that have applied LEAF-2 and v erified its performance against observational data are cited. Linkage of RA MS and TOPMODEL through LEAF-2 creates a modeling system that can be used t o explore the coupled atmosphere-biophysical-hydrologic response to altered climate forcing at local watershed and regional basin scales.