#34 Hypsometric analysis improves topography-based subgrid structures for the ACME Land Model

Abstract

Topography exerts a major control on land surface processes through its influence on atmospheric forcing, soil and vegetation properties, network topology and drainage area. Land surface spatial structure that captures spatial heterogeneity influenced by topography is expected to improve representation of land surface processes in land surface models. For example, land surface modeling using subbasins instead of regular grids as computational units has demonstrated improved scalability of simulated runoff and streamflow processes. Two methods (Global and Local) are applied to derive new land surface spatial structures by further dividing subbasins into subgrid units based on topographic properties to take advantage of the emergent patterns and scaling properties of atmospheric, hydrologic, and vegetation processes in land surface models. The Global method utilizes the elevation classification scheme employed in Leung and Ghan (1995; 1998) combined with classifications of topographic slope and aspect to discretize each subbasin into multiple subgrid units. While, in the Local method, each subbasin is divided into multiple subgrid units using elevation classes derived based on hypsometric characteristics combined with classes of topographic aspect. In this study, the relative merits of using hypsometric characteristics in deriving topography-based subgrid structures are evaluated over the topographically contrasting regions of the Northwestern United States. Results highlight the relative advantages of the Local method over the Global method in capturing topographic heterogeneity and spatial patterns of atmospheric forcing and land cover.