Watershed Grid for the Energy Exascale Earth System Model (E3SM)

1. Watershed Grid for the Energy Exascale Earth System Model (E3SM) Teklu K. Tesfa and Ruby Leung, Peter Thornton

2. Motivation: Why watershed grid? • Watershed grid representation offers distinct advantages • It follows the natural topographic divides and river network structure that governs hydrological processes • Simplifies representation of runoff schemes such as the TOPMODEL formulations Tesfa et al., 2014 a & b

3. Motivation: Why watershed grid? • Watershed grid representation offers distinct advantages • More realistic representation of land surface processes such as sediment, river transport, inundation and human impacts e.g. dams/reservoirs • Relaxed requirement for lateral water redistribution from neighboring watershed grids • Studies show clear scalability advantage compared to regular grid based land surface modeling Tesfa et al., 2014 a & b Mean Absolute Error

4. Motivation: Why watershed grid? • Watershed grid representation offers distinct advantages • Watershed grid offers an opportunity to developing a better topography-based subgrid structure • More realistic representation of topographic heterogeneity such as impacts of slope and aspect; • Option for configuring ELM-MOSART-WM on the same grid • also possibility for developing subgrid structures with hydrologic connectivity:

5. Watershed Grid Development: progress • Watershed Grid developed from high resolution elevation data • Stream network and other topographic attributes are developed from the same DEM

6. Watershed Grid Development: challenges • Delineation of watersheds located at the land-ocean interface (coastal area) require additional efforts beyond the normal watershed delineation process • Coastal outlet points identified over South American continent • The outlet points are used to delineate the coastal watersheds

7. Opportunities considered • Offline and online coupled simulations using the watershed grid • A mapping file is needed between the atmospheric grid and the watershed grid • Atmospheric model runs on grid-level only • Land model runs using watershed grid • Atmospheric fluxes are mapped onto the watershed grid • Land surfaces fluxes are mapped onto the atmospheric grid Atmospheric Grid Mapping to Watershed grid Mapping to Atmospheric grid Watershed grids

8. Discussion • The goal is to have a watershed grid-based configuration option in E3SM, with possibility to run ELM-MOSART-WM using watershed grid. For this purpose, a mapping file between atmospheric grid and watershed grid needs to be developed. • One way to implement the watershed grid configuration is to introduce a subroutine to facilitate the mapping of fluxes between the coupler and the land model component using a mapping file. • Is there other better approach to implementing the watershed-grid? • What is the implication of this to the computational demand and to the coupler?

9. Thank You!