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Hydro model channel improvements #156

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95450f3
Add option to disallow terrestrial outflow
matthewhoffman Oct 16, 2025
d51a403
Move assignment of melt input outside of SGH subcycling loop
matthewhoffman Oct 17, 2025
f20a97b
Add more timers to hydrology solve
matthewhoffman Oct 21, 2025
c2d4944
Prevent uphill outflow at terrestrial margins
matthewhoffman Oct 27, 2025
ece5ce1
disable channel melt into/out of lakes
matthewhoffman Nov 2, 2025
6cd0d58
Allow channel melt out of lakes but not into or within
matthewhoffman Nov 4, 2025
3cd22f7
Remove code that disables channel melt in lakes
matthewhoffman Nov 5, 2025
b6581ba
Disable iceThicknessHydro option by default
matthewhoffman Nov 5, 2025
30b2d3d
Add max channel area option
matthewhoffman Nov 5, 2025
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12 changes: 10 additions & 2 deletions components/mpas-albany-landice/src/Registry_subglacial_hydro.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -78,8 +78,8 @@
possible_values="positive real number"
/>

<nml_option name="config_SGH_use_iceThicknessHydro" type="logical" default_value=".true." units="unitless"
description="Option to use an altered ice thickness field called iceThicknessHydro that replaces local maxima/minima in upperSurface with a mean of the cells neighbors. This option has no significant effect on the behavior of the model but makes it more stable."
<nml_option name="config_SGH_use_iceThicknessHydro" type="logical" default_value=".false." units="unitless"
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@alexolinhager alexolinhager Nov 6, 2025

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I think we will eventually need to port your MPAS-Tools ice surface alteration code into MALI if we want to run with evolving dynamics. The primary reason for iceThicknessHydro was the development if single-cell surface depressions that formed when running coupled simulations. This was mostly an issue when running with the higher order velocity solver, which created speckled ice thicknesses along the domain edges as the run progressed.

It seems like the MPAS-Tools code should fix that issue, so I think we should try replacing the iceThicknessHydro code with what you wrote there. Would it be better to make that it's own PR, or tack it onto this one?

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@matthewhoffman matthewhoffman Nov 10, 2025

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Thanks for reminding me about the noise along the boundaries of regional domains with the higher-order advection. I think change to iceThicknessHydro should occur in a separate PR. The depression-filling algorithm in my standalone script will be a decent amount of work to port from python to fortran, I think, because it currently relies on some python libraries for a lot of the work. Alternatively, we might be able to keep the existing iceThicknessHydro but disable modifications near the GL. And maybe there is a fix to the HO advection scheme to ensure it reduces to first-order near the boundaries of regional domains (cc: @trhille). With any of those options, I think we should tackle them separately from this PR.

description="Option to use an altered ice thickness field called iceThicknessHydro that replaces local maxima/minima in upperSurface with a mean of the cells neighbors. This option has no significant effect on the behavior of the model but makes it more stable. NOTE: Current implementation causes unrealistic bumps in thickness near the grounding line in many places, which prevents realistic outflow. Enable this option with care."
possible_values=".true. or .false."
/>

Expand Down Expand Up @@ -112,6 +112,10 @@
description="width of sheet beneath/around channel that contributes to melt within the channel"
possible_values="positive real number"
/>
<nml_option name="config_SGH_chnl_max_area" type="real" default_value="500.0" units="m^2"
description="max value for channel area. If channel evolution leads to an area larger than this, it gets set back to this value. Note this will violate mass conservation, but we also do not remove channel melt mass from the ice above, so that is already a mass conservation issue."
possible_values="positive real number"
/>
<nml_option name="config_SGH_include_pressure_melt" type="logical" default_value=".false." units="none"
description="whether to include the pressure melt term in the rate of channel opening"
possible_values=".true. or .false."
Expand All @@ -129,6 +133,10 @@
description="number of iterations to smooth waterPressure over when calculating waterPressureSlopeNormal. Used only to keep channelPressureFreeze stable and will not affect other aspects of the model that rely on waterPressure."
possible_values="positive integer or zero"
/>
<nml_option name="config_SGH_allow_terrestrial_outflow" type="logical" default_value=".true." units="none"
description="whether to allow discharge out at terrestrial margins"
possible_values=".true. or .false."
/>
</nml_record>

<!-- ======================================================================= -->
Expand Down
106 changes: 77 additions & 29 deletions components/mpas-albany-landice/src/mode_forward/mpas_li_subglacial_hydro.F
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Original file line number Diff line number Diff line change
Expand Up @@ -396,18 +396,6 @@ subroutine li_SGH_solve(domain, err)
block => block % next
end do


! =============
! =============
! =============
! subcycle hydro model until master dt is reached
! =============
! =============
! =============
timecycling: do while (timeLeft > 0.0_RKIND)
numSubCycles = numSubCycles + 1


! =============
! Calculate time-varying forcing, as needed
! =============
Expand Down Expand Up @@ -436,10 +424,6 @@ subroutine li_SGH_solve(domain, err)
err = ior(err, 1)
endif

! SHMIP forcing will override basalMeltInput.
call shmip_timevarying_forcing(block, err_tmp)
err = ior(err, err_tmp)

block => block % next
end do

Expand All @@ -453,6 +437,29 @@ subroutine li_SGH_solve(domain, err)
endif



! =============
! =============
! =============
! subcycle hydro model until master dt is reached
! =============
! =============
! =============
timecycling: do while (timeLeft > 0.0_RKIND)
numSubCycles = numSubCycles + 1


! apply shmip forcing if needed
block => domain % blocklist
do while (associated(block))
! SHMIP forcing will override basalMeltInput from above
call shmip_timevarying_forcing(block, err_tmp)
err = ior(err, err_tmp)

block => block % next
end do


! =============
! Update till water layer thickness
! =============
Expand Down Expand Up @@ -482,6 +489,7 @@ subroutine li_SGH_solve(domain, err)
! =============
! Calculate edge quantities and advective fluxes
! =============
call mpas_timer_start("calc edge quantities")
block => domain % blocklist
do while (associated(block))

Expand Down Expand Up @@ -518,12 +526,14 @@ subroutine li_SGH_solve(domain, err)

block => block % next
end do
call mpas_timer_stop("calc edge quantities")


! =============
! Update Channel fields
! =============
if (config_SGH_chnl_active) then
call mpas_timer_start("update channel")
block => domain % blocklist
do while (associated(block))

Expand All @@ -539,13 +549,16 @@ subroutine li_SGH_solve(domain, err)
call mpas_dmpar_field_halo_exch(domain, 'channelMelt')
call mpas_dmpar_field_halo_exch(domain, 'channelPressureFreeze')
call mpas_timer_stop("halo updates")
call mpas_timer_stop("update channel")
endif


! =============
! Calculate adaptive time step
! =============
call mpas_timer_start("calc SGH dt")
call check_timestep(domain, timeLeft, numSubCycles, err_tmp)
call mpas_timer_stop("calc SGH dt")
err = ior(err, err_tmp)
if (err > 0) then
exit timecycling
Expand All @@ -555,6 +568,7 @@ subroutine li_SGH_solve(domain, err)
! =============
! Compute flux divergence
! =============
call mpas_timer_start("compute flux div")
block => domain % blocklist
do while (associated(block))
call mpas_pool_get_subpool(block % structs, 'mesh', meshPool)
Expand Down Expand Up @@ -591,12 +605,14 @@ subroutine li_SGH_solve(domain, err)
call mpas_timer_start("halo updates")
call mpas_dmpar_field_halo_exch(domain, 'divergence')
call mpas_timer_stop("halo updates")
call mpas_timer_stop("compute flux div")


! =============
! Update channel area now that we have time step
! =============
if (config_SGH_chnl_active) then
call mpas_timer_start("evolve channel")
block => domain % blocklist
do while (associated(block))

Expand All @@ -611,11 +627,13 @@ subroutine li_SGH_solve(domain, err)
call mpas_dmpar_field_halo_exch(domain, 'channelMeltInputCell')
call mpas_dmpar_field_halo_exch(domain, 'channelArea')
call mpas_timer_stop("halo updates")
call mpas_timer_stop("evolve channel")
endif

! =============
! Calculate total grounding line discharges
! =============
call mpas_timer_start("calc SGH GL flux")
block => domain % blocklist
do while (associated(block))

Expand All @@ -624,10 +642,12 @@ subroutine li_SGH_solve(domain, err)

block => block % next
end do
call mpas_timer_stop("calc SGH GL flux")

! =============
! Update water layer thickness
! =============
call mpas_timer_start("update water layer thickness")
block => domain % blocklist
do while (associated(block))
call mpas_pool_get_subpool(block % structs, 'geometry', geometryPool)
Expand Down Expand Up @@ -660,6 +680,7 @@ subroutine li_SGH_solve(domain, err)

block => block % next
end do
call mpas_timer_stop("update water layer thickness")

! =============
! Calculate pressure field
Expand All @@ -679,6 +700,7 @@ subroutine li_SGH_solve(domain, err)
! ordering choice is only needed to support channels. Without it, runs with
! channels would use an out of date waterThickness in the hydropotential and
! do not restart correctly due to the order of operations mismatch.
call mpas_timer_start("calc pressure")
block => domain % blocklist
do while (associated(block))

Expand Down Expand Up @@ -709,6 +731,7 @@ subroutine li_SGH_solve(domain, err)

block => block % next
end do
call mpas_timer_stop("calc pressure")

deltatSGHaccumulated = deltatSGHaccumulated + deltatSGH

Expand Down Expand Up @@ -879,6 +902,7 @@ subroutine calc_edge_quantities(block, err)
real (kind=RKIND), pointer :: bedRoughMax
real (kind=RKIND) :: conduc_coeff_wtd
character (len=StrKIND), pointer :: config_SGH_tangent_slope_calculation
logical, pointer :: config_SGH_allow_terrestrial_outflow
real (kind=RKIND), pointer :: config_sea_level
real (kind=RKIND), pointer :: rhoo
integer, pointer :: nEdges
Expand Down Expand Up @@ -909,6 +933,7 @@ subroutine calc_edge_quantities(block, err)
call mpas_pool_get_config(liConfigs, 'config_SGH_conduc_coeff_drowned', conduc_coeff_drowned)
call mpas_pool_get_config(liConfigs, 'config_SGH_bed_roughness_max', bedRoughMax)
call mpas_pool_get_config(liConfigs, 'config_SGH_tangent_slope_calculation', config_SGH_tangent_slope_calculation)
call mpas_pool_get_config(liConfigs, 'config_SGH_allow_terrestrial_outflow', config_SGH_allow_terrestrial_outflow)
call mpas_pool_get_config(liConfigs, 'config_sea_level', config_sea_level)
call mpas_pool_get_config(liConfigs, 'config_ocean_density', rhoo)

Expand Down Expand Up @@ -972,19 +997,35 @@ subroutine calc_edge_quantities(block, err)
! This one-sided implementation also creates outflowing conditions at terrestrial boundary
do iEdge = 1, nEdges
if (hydroTerrestrialMarginMask(iEdge) == 1) then
cell1 = cellsOnEdge(1, iEdge)
cell2 = cellsOnEdge(2, iEdge)
if (li_mask_is_grounded_ice(cellMask(cell1))) then ! cell2 is the icefree cell - replace phi there with cell1 Phig

hydropotentialBaseSlopeNormal(iEdge) = - waterPressure(cell1) / dcEdge(iEdge)
hydropotentialSlopeNormal(iEdge) = - (rho_water * gravity * waterThickness(cell1) + waterPressure(cell1)) / dcEdge(iEdge)

else ! cell1 is the icefree cell - replace phi there with cell2 Phig

hydropotentialBaseSlopeNormal(iEdge) = waterPressure(cell2) / dcEdge(iEdge)
hydropotentialSlopeNormal(iEdge) = (rho_water * gravity * waterThickness(cell2) + waterPressure(cell2)) / dcEdge(iEdge)

endif ! which cell is icefree
if (config_SGH_allow_terrestrial_outflow) then
cell1 = cellsOnEdge(1, iEdge)
cell2 = cellsOnEdge(2, iEdge)
if (li_mask_is_grounded_ice(cellMask(cell1))) then ! cell2 is the icefree cell - replace phi there with cell1 Phig
if (bedTopography(cell2) < bedTopography(cell1)) then
hydropotentialBaseSlopeNormal(iEdge) = - waterPressure(cell1) / dcEdge(iEdge)
hydropotentialSlopeNormal(iEdge) = - (rho_water * gravity * waterThickness(cell1) + waterPressure(cell1)) / dcEdge(iEdge)
else
! If bare ground elevation is higher than elevation beneath the ice, no flux
hydropotentialBaseSlopeNormal(iEdge) = 0.0_RKIND
hydropotentialSlopeNormal(iEdge) = 0.0_RKIND
waterPressureSlopeNormal(iEdge) = 0.0_RKIND
endif
else ! cell1 is the icefree cell - replace phi there with cell2 Phig
if (bedTopography(cell1) < bedTopography(cell2)) then
hydropotentialBaseSlopeNormal(iEdge) = waterPressure(cell2) / dcEdge(iEdge)
hydropotentialSlopeNormal(iEdge) = (rho_water * gravity * waterThickness(cell2) + waterPressure(cell2)) / dcEdge(iEdge)
else
! If bare ground elevation is higher than elevation beneath the ice, no flux
hydropotentialBaseSlopeNormal(iEdge) = 0.0_RKIND
hydropotentialSlopeNormal(iEdge) = 0.0_RKIND
waterPressureSlopeNormal(iEdge) = 0.0_RKIND
endif
endif ! which cell is icefree
else ! if disallow terrestrial outflow
hydropotentialBaseSlopeNormal(iEdge) = 0.0_RKIND
hydropotentialSlopeNormal(iEdge) = 0.0_RKIND
waterPressureSlopeNormal(iEdge) = 0.0_RKIND
endif ! if allow terrestrial outflow
endif ! if edge of grounded ice
end do

Expand Down Expand Up @@ -1844,6 +1885,7 @@ subroutine update_channel(block, err)
real (kind=RKIND), pointer :: creep_coeff
real (kind=RKIND), pointer :: rhoi
real (kind=RKIND), pointer :: config_SGH_incipient_channel_width
real (kind=RKIND), pointer :: bedRoughMax
logical, pointer :: config_SGH_include_pressure_melt
real (kind=RKIND), dimension(:), pointer :: channelArea
real (kind=RKIND), dimension(:), pointer :: channelMelt
Expand All @@ -1862,6 +1904,7 @@ subroutine update_channel(block, err)
real (kind=RKIND), dimension(:), pointer :: effectivePressureSGH
real (kind=RKIND), dimension(:), pointer :: channelDiffusivity
real (kind=RKIND), dimension(:), pointer :: waterThicknessEdgeUpwind
real (kind=RKIND), dimension(:), pointer :: waterThickness
integer, dimension(:), pointer :: waterFluxMask
integer, dimension(:), pointer :: hydroMarineMarginMask
integer, dimension(:), pointer :: edgeMask
Expand All @@ -1885,6 +1928,7 @@ subroutine update_channel(block, err)
call mpas_pool_get_config(liConfigs, 'config_SGH_chnl_creep_coefficient', creep_coeff)
call mpas_pool_get_config(liConfigs, 'config_SGH_incipient_channel_width', config_SGH_incipient_channel_width)
call mpas_pool_get_config(liConfigs, 'config_SGH_include_pressure_melt', config_SGH_include_pressure_melt)
call mpas_pool_get_config(liConfigs, 'config_SGH_bed_roughness_max', bedRoughMax)
call mpas_pool_get_dimension(meshPool, 'nVertLevels', nVertLevels)
call mpas_pool_get_dimension(meshPool, 'nEdgesSolve', nEdgesSolve)
call mpas_pool_get_array(hydroPool, 'channelArea', channelArea)
Expand All @@ -1908,6 +1952,7 @@ subroutine update_channel(block, err)
call mpas_pool_get_array(hydroPool, 'hydroMarineMarginMask', hydroMarineMarginMask)
call mpas_pool_get_array(hydroPool, 'channelDiffusivity', channelDiffusivity)
call mpas_pool_get_array(hydroPool, 'waterThicknessEdgeUpwind', waterThicknessEdgeUpwind)
call mpas_pool_get_array(hydroPool, 'waterThickness', waterThickness)
call mpas_pool_get_array(geometryPool, 'edgeMask', edgeMask)
! Calculate terms needed for opening (melt) rate

Expand Down Expand Up @@ -2029,9 +2074,11 @@ subroutine evolve_channel(block, err)
integer, dimension(:,:), pointer :: edgeSignOnCell
real (kind=RKIND), dimension(:), pointer :: areaCell
real (kind=RKIND), dimension(:), pointer :: dcEdge
real (kind=RKIND), pointer :: config_SGH_chnl_max_area
integer, pointer :: nCellsSolve
integer :: iCell, iEdgeOnCell, iEdge

call mpas_pool_get_config(liConfigs, 'config_SGH_chnl_max_area', config_SGH_chnl_max_area)
call mpas_pool_get_subpool(block % structs, 'hydro', hydroPool)
call mpas_pool_get_subpool(block % structs, 'mesh', meshPool)
call mpas_pool_get_array(hydroPool, 'deltatSGH', deltatSGH)
Expand Down Expand Up @@ -2077,6 +2124,7 @@ subroutine evolve_channel(block, err)
channelArea = channelChangeRate * deltatSGH + channelArea
! If sheet dissipation contributes to channel, there should be no need for a minimum channel size
channelArea = max(1.0e-8_RKIND, channelArea) ! make some tiny value when it goes negative
channelArea = min(config_SGH_chnl_max_area, channelArea) ! limit channel area to config-specified max value
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@alexolinhager alexolinhager Nov 6, 2025

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Would it be better to just limit channelMelt and channelPressureFreeze when channelArea exceeds config_SGH_chnl_max_area? That way the channel still wouldn't grow past the max value but we also wouldn't violate mass conservation if there was no actual unaccounted melting. Probably doesn't affect the outcome but could be cleaner to not have a cell where channelMelt far exceeds the channelArea

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@matthewhoffman matthewhoffman Nov 10, 2025

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@alexolinhager , that's a good suggestion. I'll look into how best to make the adjustment.


!--------------------------------------------------------------------
end subroutine evolve_channel
Expand Down