Two-way coupling between the sub-grid land surface and river networks in Earth system models


Over the past decade, there has been appreciable progress towards modeling the water, energy, and carbon cycles at field-scales (10–100 m) over continental to global extents. One such approach, named HydroBlocks, accomplishes this task while maintaining computational efficiency via sub-grid tiles, or Hydrologic Response Units (HRUs), learned via a hierarchical clustering approach from available global high-resolution environmental data. However, until now, there has yet to be a macroscale river routing approach that is able to leverage HydroBlocks' approach to sub-grid heterogeneity, thus limiting the added value of field-scale land surface modeling in Earth System Models (e.g., riparian zone dynamics, irrigation from surface water, and interactive floodplains). This paper introduces a novel dynamic river routing scheme in HydroBlocks that is intertwined with the modeled field-scale land surface heterogeneity. The primary features of the routing scheme include:

  1. the fine-scale river network of each macroscale grid cell’s is derived from very high resolution ($<$ 100 m) DEMs;
  2. the inlet/outlet reaches of each macroscale grid cell are linked to assemble the continental river networks;
  3. the river dynamics are solved at a reach-level via the Kinematic wave assumption of the Saint-Venant equations;
  4. a two-way coupling is established between each sub-grid tile and the river network.

To implement and test the novel approach, a 1.0-degree bounding box surrounding the Atmospheric Radiation and Measurement (ARM) Southern Great Plains (SGP) site in Northern Oklahoma (United States) is used. The results show:

  1. the implementation of the two-way coupling between the land surface and the river network leads to appreciable differences in the simulated spatial heterogeneity of the surface energy balance;
  2. a limited number of tiles (~300 per 0.25-degree cell) are required to approximate the fully distributed simulation adequately;
  3. the surface energy balance partitioning is sensitive to the river routing model parameters.

The resulting routing scheme provides an effective and efficient path forward to enable a two-way coupling between the high-resolution river networks and existing tiling schemes within Earth system models.

In Geoscientific Model Development
Noemi Vergopolan
Noemi Vergopolan
Computational Hydrology