ParFlow is an open-source, modular, parallel watershed flow model. It includes fully-integrated overland flow, the ability to simulate complex topography, geology and heterogeneity and coupled land-surface processes including the land-energy budget, biogeochemistry and snow (via CLM). It is multi-platform and runs with a common I/O structure from laptop to supercomputer. ParFlow is the result of a long, multi-institutional development history and is now a collaborative effort between CSM, LLNL, UniBonn and UCB. ParFlow has been coupled to the mesoscale, meteorological code ARPS and the NCAR code WRF. Thank you to all the ParFlow contributors, both past and present. Recent contributors may be found here: https://github.com/parflow/parflow/graphs/contributors ParFlow Version 3.6.0 Overview of Changes New overland flow boundary conditions Flow barrier added Support for metadata file Boundary condition refactoring Bug fixes Coding style update User Visible Changes New overland flow boundary conditions Three new boundary conditions as modules - OverlandKinematic, OverlandDiffusive and Seepage. OverlandKinematic is similar to the original OverlandFlow boundary condition but uses a slightly modified flux formulation that uses the slope magnitude and it is developed to use face centered slopes (as opposed to grid centered) and does the upwinding internally.x. See user manual for additional information on the new boundary conditions. New test cases were added exercising the new boundary conditions: overland_slopingslab_DWE.tcl, overland_slopingslab_KWE.tcl, overland_tiltedv_DWE.tcl, overland_tiltedV_KWE.tcl, Overland_FlatICP.tcl Two new options were added to the terrain following grid formulation to be consistent with the upwinding approach used in the new overland flow formulation these are specified with the new TFGUpwindFormullation keys documented in the manual. For both OverlandDiffusive and OverlandKinematic analytical jacobians were implemented in the new modules and these were tested and can be verified in the new test cases noted above. Flow barrier added Ability to create a flow barrier capability equivalent to the hydraulic flow barrier (HFB) or flow and transport parameters at interfaces. The flow barriers are placed at the fluxes as scalar multipliers between cells (at cell interfaces). Flow barriers are set using a PFB file, see user manual for additional information. The flow barrier is turned off by default. Support for metadata file A metadata file is written in JSON format summarizing the inputs to a run and its output files. This file provides ParaView and other post-processing tools a simple way to aggregate data for visualizations and analyses. Metadata is collected during simulation startup and updated to include timestep information with each step the simulation takes. It is rewritten with each timestep so that separate processes may observe simulation progress by watching the file for changes. Bug Fixes Fixed segmentation fault when unitialized variable was referenced in cases with processors is outside of the active domain. Internal Changes Boundary condition refactoring The framework for boundary conditions was significantly refactored to provide a macro system to simplify adding new boundary conditions. See bc_pressure.h for additional documentation. Coding style update The Uncrustify coding style was updated and code was reformated.

{"references": ["Jones, J.E. and Woodward, C.S. (2001). Newton\u2013Krylov-multigrid solvers for large-scale, highly heterogeneous, variably saturated flow problems. Advances in Water Resources, 24(7), 763\u2013774, doi:10.1016/S0309-1708(00)00075-0.", "Ashby S.F. and Falgout, R.D. (1996). A Parallel Multigrid Preconditioned Conjugate Gradient Algorithm for Groundwater Flow Simulations. Nuclear Science and Engineering, 124(1), 145-159.", "Kollet, S.J. and Maxwell, R.M. (2006). Integrated surface-groundwater flow modeling: a free-surface overland flow boundary condition in a parallel groundwater flow model. Advances in Water Resources, 29(7), 945-958, doi:10.1016/j.advwatres.2005.08.006.", "Maxwell, R.M. (2013) A terrain-following grid transform and preconditioner for parallel, large-scale, integrated hydrologic modeling. Advances in Water Resources, 53, 109-117, doi:10.1016/j.advwatres.2012.10.001.", "Maxwell, R.M. and Miller, N.L. (2005). Development of a Coupled Land Surface and Groundwater Model. Journal of Hydrometeorology, 6(3), 233-247, doi:10.1175/JHM422.1.", "Kollet, S.J. and Maxwell, R.M. (2008). Capturing the influence of groundwater dynamics on land surface processes using an integrated, distributed watershed model. Water Resources Research, 44(2), W02402, doi:10.1029/2007WR006004"]}