Developments in continental-scale, integrated hydrologic modeling: ParFlow-CONUS version 2.0

High-resolution, continental scale hydrologic models have increased in use and application. These models enable in-depth analysis of interactions between hydrologic phenomena beyond catchment boundaries and across scales. Model intercomparisons and validation have prompted us to improve model configurations and infrastructure. We present ParFlow-CONUS version 2 (PF-CONUSv2), a continental scale, integrated hydrologic model. PF-CONUSv2 is an expansion the first version of PF-CONUS (PF-CONUSv1), which is based on a rectangular domain covering most of the continental United States and has been used in numerous studies including evaluating the connection between groundwater and transpiration, large-scale groundwater depletion on streamflow, and shallow groundwater response to climate warming. The PF-CONUSv2 domain incorporates the entirety of the continental US, including basins that extend into Canada and Mexico. Extensive testing of a combination of subsurface configurations has led to a deeper and more complex subsurface parameterization, expanding from 5 subsurface layers in PF-CONUSv1 to 10 layers in PF-CONUSv2. This expansion of active cells in the vertical and lateral directions results in a 150% increase in model domain, from 31.5 million total compute cells in PF-CONUSv1, to 78.5 million in PF-CONUSv2; and now includes a subsurface flow barrier and coastal interactions. Additionally, topographic processing and overland flow testing have improved the representation of the land surface and led to hydrologically consistent topography. We present streamflow and groundwater results from both the steady-state model spin-up and the preliminary transient simulations, forced with CW3E Retrospective Forcing. This research is the first demonstration of the potential applications of the PF-CONUSv2 model for analysis of continental-scale hydrologic cycle interactions from the bedrock to top-of-canopy.