ParFlow hydrologic model

• Richards' equation for variably saturated 3D subsurface flow
• Shallow water equations for surface flow
• Modular, coupled land model that represents full energy budget, vegetative and snow processes
• Robust nonlinear solvers (using the Kinsol Newton-Krylov package) and efficient multigrid linear solver (using the Hypre package)
• Parallel implementation using multiple approaches and architectures
• Excellent parallel scalability with production runs of more than 30k processors
• Support for OpenMP and CUDA for use on accelerator architectures such as GPUs
• Data formats such as SILO and NetCDF4
• Implementation on different architectures and operating systems from "Laptop to Supercomputer" (single CPU, Linux clusters, highly scalable systems such as IBM Blue Gene) with the same source code and input on all platforms
• Widespread use on many institutional computer systems including many of the fastest supercomputers in the world (e.g. Edison, Cori, Yellowstone, JUQUEEN)
• Application to a wide range of hydrology problems and basins from small headwaters catchment to the continent
• Broad community development and use
• Extensive automated testing framework that follows best software practices
• Implementation as a Docker instance for easy and efficient deployments
• Large set of utilities for pre- and postprocessing and diagnistics calculations
• Flexible and portable cmake built environment

• Lagrangian particle tracking to simulate water residence time, surface subsurface exchange and contaminant transport
• Adaptive mesh refinement unsing p4est
• Extreme scaling capability up to more than 400k processors
• Geochemical reactive transport with higher order advection schemes and reaction kinetics using CRUNCH
• NetCDF CF meta-data convention for portability, provenance and worflow integration
• In-situ visualisation and processing using VisIt
• JUBE provenance-enabled work flow engine implementation for efficient development, benchmarking and run-control
• Integrated water management including pumping, irrigation and diversions

Soil moisture monitoring and forecasting for agriculture over central Europe In the context of more frequent and consecutive droughts during the vegetation period over the last years (e.g. 2018, 2019, and 2020) in central Europe, we use ParFlow/CLM at ~600m resolution to monitor and forecast the soil water budget over Germany and the neighboring regions.
The deterministic medium-range forecast over 10 days is extended by a 50 member ensemble to account for the uncertainty of the forecast, and especially precipitation, and its impact on the soil water budget.
In addition, subseasonal probabilistic ensemble forecasts (3 months lead time) are calculated a few times per year to help farmers and their advisors to manage the water resources over a longer time span. Several parameters that are relevant for the stakeholders from the agricultural sector are derived from the standard ParFlow outputs, providing information on various aspects of the soil water budget for different root depths, e.g. plant available water, seepage water, subsurface water storage change, groundwater recharge, water table depth, and saturation.

Transient, integrated simulation of groundwater and surface water over the Continental US A representation of pre-development groundwater, surface water, and surface energy processes, which are driven by hourly forcing by NLDAS-II from the 1985 water year. At 1km lateral resolution, with 12TB of model output and 3TB of input, this is the first large-scale, high resolution simulation of its kind, capable of resolving complex interactions between climate, water and topography.

Groundwater-surface water interactions in the San Joaquin River Basin As one of the most productive agricultural regions of the United States and a major water resource for a growing population, the San Joaquin River basin in the Central Valley in California, is a case study in the water-food-energy nexus and sensitivity to a changing climate. Here, we seek to better understand the physical hydrology of the basin by simulating groundwater-surface water dynamics with ParFlow-CLM. Results suggest that mountain block hydraulic conductivity could account for 7-23% of total recharge in the Central Valley, an important finding for water resource management in California.

Groundwater-land surface-atmosphere feedbacks during the European 2003 heat wave By coupling ParFlow to land and meteorological models, the fully coupled water cycle from groundwater to atmosphere can be simulated, a novel exploration in that atmospheric models rarely incorporate a dynamic water table and three dimensional subsurface flow. This study couples ParFlow to the meteorological model over Europe during the 2003 heat wave in order to investigate the effects of various lower boundary conditions and configurations on land-atmosphere moisture exchange and thermal energy.

Continental water residence times Ever wonder how long water spends in the subsurface? Residence time and groundwater age are vital to ecosystem development and human consumption, but measuring residence time distributions is difficult at large scales. ParFlow may be used to estimate water residence time when used in conjunction with a Lagrangian particle tracking approach. A simulation of groundwater age across the continental United States allows unique insight into the relationship between geography, climate, and water residence time in major basins.

The effects of insect-induced tree mortality on water and energy in mountain headwaters The mountain pine beetle (MPB) has decimated the high elevation lodgepole and ponderosa pine forests of Western United States and Canada over the past two decades. ParFlow-CLM was used to diagnose feedbacks that land disturbance at this scale has on water and energy fluxes in the Big Thompson watershed in Colorado. Results show that insect-induced reductions in canopy interception, transpiration, and snow pack are largely mitigated by heightened ground evaporation and ablation, adding to the growing number of studies citing damping of MPB hydrologic signal at large scales.

Scale dependent parameterization in integrated hydrologic modeling The highly instrumented Wüstebach catchment in Germany allows the unique opportunity to explore the application of the information entropy concept in subsurface parameterization of three dimensional hydrological models. Results suggest that amplifying soil hydraulic conductivity in regions where aggregation of observations at model scale leads to loss of topographic information content may increase model performance, an important finding for high-resolution, large-scale physically based modeling that requires detailed subsurface parameterization.

Moisture dependent irrigation and its feedbacks with integrated hydrology In this example, ParFlow was used in conjunction with a novel linear optimization water allocation module to evaluate the impact of groundwater-surface water interactions on moisture dependent irrigation in the Little Washita River Basin, Oklahoma.

Modeling the Critical Zone in an ephemeral West-African Monsoon system West-African hydrosystems are driven by seasonal monsoon dynamics with high variability. While the extreme drought in the 70's and 80's was surprisingly associated with runoff and water table recharge increase and (due to simultaneous land use change) in the Sahel, consequences in the southern, more humid Sudanian zone were a major drop in streamflow. Streamflow generation processes in this area involve subsurface processes (as opposed to Hortonian-dominated Sahelian processes) including temporary connexion of perched and permanent water table. Water table drawdown during the dry season is controlled by land cover distribution and dominated by tree transpiration. This highly connected critical zone system (see e.g. Hector et al., 2015) requires integrated modeling to assess sensitivities to global changes and guide policymakers in this part of the world. The fully coupled ParFlow-CLM simulation of a small watershed in northern Benin (the Ara catchment) shows the intermittent streamflow generation (surface saturation as blue patches), saturation variations in the surface and unsaturated zone, and both permanent and perched water table changes (saturated, deep blue zones in the bottom of the domain) as a response of the interplay between precipitation (spatially uniform, temporally variable) and evapotranspiration (different vegetation classes across the domain). This simulation was successfully compared to a complete dataset (streamflow, water table, soil moisture, evapotranspiration, water storage...) produced by the AMMA-CATCH observatory (http://www.amma-catch.org/). It allowed to assess the importance in vegetation spatial distribution in partitionning the different terms of the water budget and thus calls to enhance the inclusion of land cover.