While the catchment-scale stream-hillslope continuum is increasingly understood as a key determinant of land surface water/energy balances, the Earth System Model (ESM) community still lacks a proper hydrologic framework to capture water/energy exchanges in vertical and lateral directions between the unsaturated soil, saturated groundwater, and river/stream. To fill this gap, we develop a new modeling framework Soil, Hillslope Aquifer, and River Continuum (SHARC) integrated with the Geophysical Fluid Dynamics Laboratory (GFDL) Land Model (LM4). The LM4.1-SHARC employs the Boussinesq approximation to represent lateral groundwater fluxes and enables 1) accounting for the local horizontal hydraulic gradient between the riparian zone and stream as the driver of the stream-hillslope exchanges and 2) characterization of the hillslope aquifer based on its effective parameters (e.g., hydraulic diffusivity, and bedrock slope) through the method of streamflow recession analysis (i.e., hydraulic groundwater theory). We apply the LM4.1-SHARC model to the Pr ovidence headwater catchment at Southern Sierra, NV, and compare the model simulations with the available in-situ observations, including soil moisture, temperature, and baseflow. As a proof of concept, we show that the catchment-scale hillslope aquifer can be optimized, in terms of flux accuracy of soil drainage (vertical) and baseflow (lateral), by tuning the groundwater diffusivity and slope. In addition to the demonstration of enhanced water/energy budget simulations, we investigate the implications of a more comprehensive treatment of continuum processes such as impeded/facilitated soil drainage due to the stream-groundwater interactions to anthropogenic warming on a decadal to century scale.  

We describe the baseline model configuration and simulation characteristics of GFDL’s Atmosphere Model version 4.1 (AM4.1), which builds on developments at GFDL over 2013–2018 for coupled carbon-chemistry-climate simulation as part of the sixth phase of the Coupled Model Intercomparison Project. In contrast with GFDL’s AM4.0 development effort, which focused on physical and aerosol interactions and which is used as the atmospheric component of CM4.0, AM4.1 focuses on comprehensiveness of Earth system interactions. Key features of this model include doubled horizontal resolution of the atmosphere (~200 km to ~100 km) with revised dynamics and physics from GFDL’s previous-generation AM3 atmospheric chemistry-climate model. AM4.1 features improved representation of atmospheric chemical composition, including aerosol and aerosol precursor emissions, key land-atmosphere interactions, comprehensive land-atmosphere-ocean cycling of dust and iron, and interactive ocean-atmosphere cycling of reactive nitrogen. AM4.1 provides vast improvements in fidelity over AM3, captures most of AM4.0’s baseline simulations characteristics and notably improves on AM4.0 in the representation of aerosols over the Southern Ocean, India, and China—even with its interactive chemistry representation—and in its manifestation of sudden stratospheric warmings in the coldest months. Distributions of reactive nitrogen and sulfur species, carbon monoxide, and ozone are all substantially improved over AM3. Fidelity concerns include degradation of upper atmosphere equatorial winds and of aerosols in some regions.