HydroBlocks v0.2: enabling a field-scale two-way coupling between the land surface and river networks in Earth system models

Abstract

Abstract. 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 in Earth system models (ESMs). One such approach, named HydroBlocks, accomplishes this task while maintaining computational efficiency via Hydrologic Response Units (HRUs), more commonly known as “tiles” in ESMs. In HydroBlocks, these HRUs are learned via a hierarchical clustering approach from available global high-resolution environmental data. However, until now there has yet to be a river routing approach that is able to leverage HydroBlocks' approach to modeling field-scale heterogeneity; bridging this gap will make it possible to more formally include riparian zone dynamics, irrigation from surface water, and interactive floodplains in the model. This paper introduces a novel dynamic river routing scheme in HydroBlocks that is intertwined with the modeled field-scale land surface heterogeneity. Each macroscale polygon (a generalization of the concept of macroscale grid cell) is assigned its own fine-scale river network that is derived from very high resolution (∼ 30 m) digital elevation models (DEMs); the inlet–outlet reaches of a domain's macroscale polygons are then linked to assemble a full domain's river network. The river dynamics are solved at the reach-level via the kinematic wave assumption of the Saint-Venant equations. Finally, a two-way coupling between each HRU and its corresponding fine-scale river reaches is established. To implement and test the novel approach, a 1.0∘ 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 HRUs (∼ 300 per 0.25∘ cell) are required to approximate the fully distributed simulation adequately, and (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 state-of-the-art tiling schemes in ESMs.

Spatial Variation in Catchment Response to Climate Change Depends on Lateral Moisture Transport and Nutrient Dynamics

“…If similar relationships exist at larger scales, or if these models are run at much finer scales in the future, water and nutrient loss and subsidy could be important for their simulations of future landscape response. The need for continued research into the importance of lateral flow in large-scale land surface modelling is supported by our results, such as recent efforts in representing lateral subsurface flow in the Community Land Model (Swenson et al, 2019) and in the development of hybrid approaches using nested representation of land surface processes including lateral transport (Chaney et al, 2021). Interestingly, we did not find clear differences in annual scale ecohydrologic trends related to aspect in our results.…”

Towards an Optimal Representation of Sub‐Grid Heterogeneity in Land Surface Models

“…For each time step, the height bands, as defined by the tiling scheme, dynamically interact laterally via subsurface flow computed as a Darcy flux between adjacent bands at each subsurface level (Chaney et al., 2018). These terms are included as divergences within the one‐dimensional solution of the Richards' equation in the Noah‐MP implementation for each tile belonging to the height band (Chaney et al., 2021). In this study, HydroBlocks is run at an effective 30‐m spatial resolution and 1‐hr temporal resolution from 2012 to 2018; the first 2 years are used as a model spin‐up period.…”

“…One flexible land surface modeling framework accounting for multidimensional clustering, subbasin structure, and inter-tile interactions is HydroBlocks (Chaney, Metcalfe, & Wood, 2016;Chaney et al, 2018Chaney et al, , 2021. HydroBlocks uses a Hierarchical Multivariate Clustering (HMC) scheme to determine the tiles' configuration within the modeling domain coupled to the traditionally used NOAH-MP vertical LSM (Niu et al, 2011).…”

A Catchment‐Based Hierarchical Spatial Tessellation Approach to a Better Representation of Land Heterogeneity for Hyper‐Resolution Land Surface Modeling

“…They showed that these units can capture the heterogeneity of topography, climate, and vegetation effectively and robustly. Chaney et al (2021) further developed their hierarchical clustering approach, namely HydroBlocks v0.2, to model field-scale heterogeneity. In HydroBlocks v0.2, a fine-scale river network is coupled with the catchment-based hydrologic response units to model river routing dynamics in large-scale earth system models.…”