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.
Highlights
Recent years have seen a renewed effort to improve the representation of land surface heterogeneity in Earth system models (ESMs) (Chaney et al, 2018; Newman et al, 2014; Clark et al, 2015b; Fan et al, 2019)
The primary features of the novel river routing scheme include (1) each macroscale polygon being assigned its own fieldscale river network delineated from digital elevations models (DEMs), (2) the fine-scale inlet–outlet reaches of the macroscale polygons being linked to assemble the continental river networks, (3) river dynamics being solved at the reach-level via an implicit solution of the kinematic wave simplification of the Saint-Venant equations, and (4) a two-way coupling that is established between hydrologic response units (HRUs) and the river network
This section focuses on a simulated inundation event to provide a general understanding of the simulated land surface, routing scheme, and floodplain dynamics
Summary
Recent years have seen a renewed effort to improve the representation of land surface heterogeneity in Earth system models (ESMs) (Chaney et al, 2018; Newman et al, 2014; Clark et al, 2015b; Fan et al, 2019). This effort is driven in part by the limitations of existing upscaling parameterizations to adequately simulate the multi-scale interactions between the water, energy, and carbon cycles (Wood et al, 2011; Bierkens et al, 2014). Chaney et al.: HydroBlocks v0.2 verge on the desired meter-scale modeling while minimizing computational expense
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