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Variations in topographic downscaling impacts of atmospheric forcing across different regions of CONUS in ELM

Presentation Date
Tuesday, December 12, 2023 at 8:30am - Tuesday, December 12, 2023 at 12:50pm
MC - Poster Hall A-C - South



There are various ongoing research efforts to improve the representations of the effects of small-scale land surface heterogeneity, which are not well represented in current Earth System Models (ESMs). In this study, the effects of topography-based subgrid structure (TGU) combined with downscaling of atmospheric forcing introduced in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) are evaluated. For this purpose, ELM offline simulations are performed using two model configurations with (ELMD) and without (ELMNoD) downscaling of the grid cell mean atmospheric forcing onto the TGUs of the land model, using the same land surface properties. Here downscaling of atmospheric forcing is performed using only information of the subgrid topography. The effects of TGU and downscaling of atmospheric forcing on land surface processes are then evaluated over the contiguous US (CONUS) and regions within CONUS determined from the season of maximum precipitation and topography-based indices. The CONUS level results generally suggest that ELMD generates more snowfall and SWE, and higher runoff and less ET during spring and summer. Regional comparisons across the CONUS show that the effects of downscaling vary across the different regions. The effects of downscaling are more pronounced over regions which receive their maximum precipitation during SON and DJF compared to those of MAM and JJA and in regions where most of the TGUs are above the grid cell mean elevation. Furthermore, ELMD predicted observed SWE better than ELMNoD at 83% of SNOTEL sites, with the best performance over more topographically heterogeneous areas. The results in this study highlight the importance of improving representation of the effects of small-scale climatic heterogeneity due to topography in ESMs and motivate future research to understand the impacts of small-scale surface heterogeneity on land-atmosphere interactions over mountainous regions.

Funding Program Area(s)