Effects of Subgrid Topography on Simulations of Land Surface Processes in an Earth System Model

Abstract:

Topography has many impacts on land surface processes through its effects on atmospheric forcing, partitioning of surface fluxes, surface hydrology, and other processes. However, the effects of its subgrid heterogeneity of topography are not well represented in current Earth System Models (ESMs). Recently, a new topography-based subgrid structure has been implemented within the hierarchical subgrid spatial structure of the Energy Exascale Earth System Model (E3SM) Land Model (ELM) to improve representation of land surface processes, with minimal increase in computational demand, while improving the ability to capture the spatial heterogeneity of atmospheric forcing and land cover influenced by topography. Also, methods of downscaling of atmospheric forcing from grid cell mean to subgrid topographic units have been implemented to capture the effects of subgrid topography on atmospheric processes. This study focuses on evaluation of the impacts of the new subgrid structure and the downscaling methods on simulations of land surface processes. More specifically, ELM simulations with and without subgrid topography and driven by grid cell mean atmospheric forcing will be compared to isolate the impacts of the subgrid topography on the simulated land surface states and fluxes. Furthermore, the impacts of the subgrid topographic structure combined with spatial downscaling of atmospheric forcing on land surface modeling will be evaluated by comparing the results with observations and simulations forced by the grid cell mean precipitation in topographically heterogeneous regions.