eCLM-ParFlow Coupling Notes

[kvrigor]

(migrated from internal issue tracker)

General notes

• The test setup is based on Theresa Boas' test case for the NRW domain (300x300).
• The setup for the ParFlow domain uses 30 sublayers.
• eCLM's subsurface discretization uses levgrnd = 25 layers, of which levsoi = 20 are hydrologically and biogeochemically active. The deepest 5 layers are only included in the thermodynamical calculations.

Coupled fields

• The relevant history files can be found at /p/largedata/slts/rigor1/pfeclm_logs/NRW_300x300:

[E] eclm_nrw_300x300.clm2.h0.2017-01-01-00000.nc
[P] parflow_nrw_300x300.out.00001.nc

• Note that the sublayer indexing in eCLM and ParFlow are different!

***** Subsurface level indexing convention *****
    eCLM:  1=topmost layer, 25=deepest layer
 ParFlow: 29=topmost layer,  0=deepest layer
************************************************

• The output fields in the next subsections are labeled [E] if it is from eCLM [P] if it is from ParFlow.

Pressure head (ParFlow->eCLM)

• Units: mm
• pressure from ParFlow is copied to PFL_PSI_GRC in eCLM. PFL_PSI_GRC is a gridcell-based field that is further resolved into a subgrid-based field called SMP.
• ParFlow implementation, eCLM implementation

[P] pressure(time, z, y, x)
[E] PFL_PSI_GRC(time, levgrnd, lat, lon)
[E]         SMP(time, levgrnd, lat, lon)

H2O soil liquid (ParFlow->eCLM)

• Units: mm, kg/m^2
• Soil liquid in ParFlow is computed and then sent to PFL_SOILLIQ_GRC in eCLM. PFL_SOILLIQ_GRC is a gridcell-based field that is further resolved into a subgrid-based field called SOILLIQ.
• ParFlow implementation, eCLM implementation

[P] <soil liq not saved in ParFlow>
[E] PFL_SOILLIQ_GRC(time, levgrnd, lat, lon)
[E]         SOILLIQ(time,  levsoi, lat, lon)

Evapotranspiration (eCLM->ParFlow)

• Units: mm/s
• Root<->soil water exchange from eCLM is sent to ParFlow as evaptrans. Infiltration is accounted for at the top subsurface layer.
• eCLM implementation, ParFlow implementation

[E] QPARFLOW(time, levsoi, lat, lon)
[P] evaptrans(time, z, y, x)

Ice impedance (eCLM->ParFlow)

• EXPERIMENTAL FEATURE (see comment below)
• unitless, value ranges between 0.00-1.00
• Ice impedance (in eCLM) is a function of ice content and quantifies the increased tortuosity of the water flow when part of the pore space is filled with ice.
• In ParFlow, ice impedance is interpreted as a flow barrier—a dimensionless scalar quantity that reduces flow rate across a cell face.
• eCLM implementation, ParFlow implementation

[E] ICE_IMPEDANCE(time, levgrnd, lat, lon)
[P] ice_impedance(time, z, y, x)

Miscellaneous

• The subsurface porosity and permeability information can be found at parflow_nrw_300x300.out.00000.nc.

perm_x(time, z, y, x)
perm_y(time, z, y, x)
perm_z(time, z, y, x)
porosity(time, z, y, x)
specific_storage(time, z, y, x)
slopex(time, y, x)
slopey(time, y, x)
DZ_Multiplier(time, z, y, x)

• Model configuration files can be found here: NRW_ParFlow-eCLM
• Development branches: parflow/dev-soil-ice, eCLM/dev-soil-ice

[kvrigor]

Meeting notes 05.03.2024 (with @skollet)

1. Ice impedance is not sufficient to properly model multi-phase subsurface flow.

• Soil water in eCLM contains liquid and ice part, while ParFlow only contains liquid part. This means that porosity and pressure head in ParFlow has to be corrected in eCLM to take into account ice content, and then send the corrected fields back to ParFlow. Basically, porosity and pressure head in ParFlow has to be changed such that it becomes a function of ice content.
• The proposed implementation above, even if it can be done, is still subject to debate. Furthermore, there are no thermodynamic checks in ParFlow to guarantee the energy balance of the eCLM-ParFlow coupled system.
• Hence, ParFlow with ice impedance will remain an experimental feature until a suitable ice coupling strategy has been decided. It is still available to those who are interested to check this feature.

2. New ParFlow features (not yet planned to be implemented; to be discussed in the future)

• New overland flow boundary condition
• ParFlow with temperature (ParFlowE)