LM4-SHARC v1.0: Resolving the catchment-scale soil-hillslope aquifer-river continuum for the GFDL Earth system modeling framework

Catchment-scale representation of the groundwater and its interaction with other parts of the hydrologic cycle is crucial for accurately depicting the land water-energy balance in Earth system models (ESMs). Despite existing efforts to describe the groundwater in the land component of ESMs, most ESMs still need a prognostic framework for describing catchment-scale groundwater based on its emergent properties to understand the implications for the broader Earth system. To fill this gap, we developed a new parameterization scheme to resolve the groundwater and its two-way interactions with the unsaturated soil and stream at the catchment scale. We implemented this new parameterization scheme (SHARC, or the soil-hillslope aquifer-river continuum) in the Geophysical Fluid Dynamics Laboratory (GFDL) land model (i.e., LM4-SHARC) and evaluated its performance. By bridging the gap between hydraulic groundwater theory and ESM land hydrology, the new LM4-SHARC provides a path to learning groundwater emergent properties from available streamflow data (i.e., recession analysis), enhancing the representation of subgrid variability in water-energy states induced by the groundwater. LM4-SHARC has been applied to the Providence headwater catchment at Southern Sierra, NV, and tested against in situ observations. We found that LM4-SHARC leads to noticeable improvements in the representation of key hydrologic variables such as streamflow, near-surface soil moisture, and soil temperature. In addition to enhancing the representation of the water and energy balance, our analysis showed that accounting for groundwater convergence can induce a more significant hydrologic contrast, with higher sensitivity of soil water storage to groundwater properties in the riparian zone. Our findings indicate the feasibility of incorporating two-way interactions among groundwater, unsaturated soil, and streams into the hydrological components of ESMs and show a further need to explore the implications of these interactions in the context of Earth system dynamics.

Duke Scholars

Author Nathaniel Chaney Civil and Environmental Engineering