Wetland update by swensosc · Pull Request #3893 · ESCOMP/CTSM

swensosc · 2026-03-26T17:58:49Z

Description of changes

biogeophysics: 1) a couple of modifications to how surface water is treated. One deals with reconciling snow / h2osfc fractional areas when they coexist. Previously fh2osfc was reduced, now reduce each proportionately to ensure a maximum sum of 1. 2) change drainage from surface water to be based on matric potential gradient instead of saturated hydraulic conductivity.
biogeochemistry: add a surface layer to the methane transport calculations. This ensures that oxidation occurs in the unsaturated column calculations when the water table is at the surface.

Specific notes

Contributors other than yourself, if any:

CTSM Issues Fixed (include github issue #):

Are answers expected to change (and if so in what way)?

Any User Interface Changes (namelist or namelist defaults changes)?

Does this create a need to change or add documentation? Did you do so?

Testing performed, if any:
(List what testing you did to show your changes worked as expected)
(This can be manual testing or running of the different test suites)
(Documentation on system testing is here: https://github.com/ESCOMP/ctsm/wiki/System-Testing-Guide)
(aux_clm on derecho for intel/gnu and izumi for intel/gnu/nag/nvhpc is the standard for tags on master)

NOTE: Be sure to check your coding style against the standard
(https://github.com/ESCOMP/ctsm/wiki/CTSM-coding-guidelines) and review
the list of common problems to watch out for
(https://github.com/ESCOMP/CTSM/wiki/List-of-common-problems).

wwieder

Sorry I didn't get very far on this. We can talk more in a bit

src/biogeochem/ch4Mod.F90

wwieder

few more comments

src/biogeophys/SaturatedExcessRunoffMod.F90

src/biogeophys/SoilHydrologyInitTimeConstMod.F90

src/biogeophys/SurfaceWaterMod.F90

bld/namelist_files/namelist_defaults_ctsm.xml

src/biogeochem/ch4Mod.F90

slevis-lmwg · 2026-03-27T16:34:38Z

src/biogeochem/ch4Mod.F90

+         c = filter_methc (fc)
+         source(c,j,1) = -surface_layer_ch4_oxid(c)  ! [mol/m3-total/s]
+         source(c,j,2) = -surface_layer_o2_oxid(c)   ! O2 [mol/m3/s]
+         ! not adding error checks ...


@swensosc will double-check this comment.

src/biogeochem/ch4Mod.F90

src/biogeophys/SurfaceWaterMod.F90

wwieder

one more comment based on our paired review.

resolving this one will make it easier to see diffs in the PR.

src/biogeochem/ch4Mod.F90

ekluzek · 2026-03-27T18:10:34Z

src/biogeochem/ch4Mod.F90

+    ! Add surface layer ch4 and convert mol CH4 to g C
    do fc = 1, num_nolakec
       c = filter_nolakec(fc)
-!!$       l = col%landunit(c)


Thanks for removing the commented out code!

ekluzek

I just took a quick look to see what we have here. I ask a couple questions. But, I think it's cool that you were able to improve the science, by also reducing code duplication.

src/biogeophys/SaturatedExcessRunoffMod.F90

ekluzek · 2026-03-27T18:56:46Z

src/biogeochem/ch4Mod.F90


  end subroutine ch4_ebul

-  !#


I expected this would be moving this section of code somewhere else. But, it looks like it's just removing a ton of things.

I take it that ch4_tran and ch4_tran_surface_layers must have been almost identical, so you were able to just remove the differences in the one? That's a great improvement if so.

This does make it hard to assess what those differences were though. Maybe we could do the difference by hand and add it to the PR. I might do that, if I get to it...

Actually, there were many differences. I had kept the original routine during development, but we decided it was not needed, and thus removed it.

swensosc · 2026-03-27T20:12:23Z

the buildnamelist change worked (i.e. no default is required for 'h2osfc' method), but I noticed that it means control%stream_fldFileName_ch4finundated (in src/cpl/share_esmf/ch4FInundatedStreamType.F90) will never be set because the namelist is not read if the 'h2osfc' method is active. That means that later, in ch4Mod, this will always be true: ch4_inst%ch4findstream%useStreams(), because UseStreams checks whether stream_fldFileName_ch4finundated) == ''. The former will be false because it is not set, nor initialized.

update: adding this 2nd conditional to useStreams would ensure correct behavior for 'h2osfc':
if ( trim(control%stream_fldFileName_ch4finundated) == '' .or. finundation_mtd == finundation_mtd_h2osfc)then

slevis-lmwg

Thank you @swensosc
seems cleaner this way, and I was able (in this quick look) to notice a few minor things that I suggested fixing this time around.

Also, would you be willing to add/commit/push the conditional that you proposed in #3893 (comment) (or in our separate emails), to provide me with a concrete starting point? If the question is whether to move the check from run-time to build, then I will feel more confident making the change after seeing your initial implementation.

slevis-lmwg · 2026-03-27T22:09:38Z

src/biogeochem/ch4Mod.F90

  ! Non-tunable constants
  real(r8) :: rgasm  ! J/mol.K; rgas / 1000; will be set below
  real(r8), parameter :: rgasLatm = 0.0821_r8 ! L.atm/mol.K
+  real(r8), parameter :: psi_fc = 3.4e3       ! matric potential at field capcity (mm)


Suggested change

real(r8), parameter :: psi_fc = 3.4e3 ! matric potential at field capcity (mm)

real(r8), parameter :: psi_fc = 3.4e3_r8 ! matric potential at field capcity (mm)

slevis-lmwg · 2026-03-27T22:11:33Z

src/biogeochem/ch4Mod.F90

     if ( .not. readv ) call endrun(msg=trim(errCode)//trim(tString)//errMsg(sourcefile, __LINE__))
     params_inst%f_ch4=tempr
-
+     


Suggested change

I just noticed these. Best to take out the blank spaces here and elsewhere to keep the code neat :-)

slevis-lmwg · 2026-03-27T22:13:35Z

src/biogeochem/ch4Mod.F90


    integer  :: nstep                       ! time step number
-    character(len=32) :: subname='ch4_tran' ! subroutine name
+    character(len=32) :: subname='ch4_tran_surface_layers' ! subroutine name


Suggested change

character(len=32) :: subname='ch4_tran_surface_layers' ! subroutine name

character(len=32) :: subname='ch4_tran' ! subroutine name

slevis-lmwg · 2026-03-27T22:16:25Z

src/biogeochem/ch4Mod.F90

+                     end if
+                     diffus(c,j) = (d_con_g(s,1) + d_con_g(s,2)*t_soisno_c) * 1.e-4_r8 * &
+                          (om_frac * f_a**(10._r8/3._r8) / watsat(c,1)**2._r8 + &
+                          (1._r8-om_frac) * eps**2._r8 * f_a**(3._r8 / bsw(c,1)) ) &


I'm told multiplication is much more efficient than raising exponents, so:

Suggested change

(1._r8-om_frac) * eps**2._r8 * f_a**(3._r8 / bsw(c,1)) ) &

(1._r8-om_frac) * eps*eps * f_a**(3._r8 / bsw(c,1)) ) &

slevis-lmwg · 2026-03-27T22:16:59Z

src/biogeochem/ch4Mod.F90

+                     end if
+                     diffus (c,j) = (d_con_g(s,1) + d_con_g(s,2)*t_soisno_c) * 1.e-4_r8 * &
+                          (om_frac * f_a**(10._r8/3._r8) / watsat(c,j)**2._r8 + &
+                          (1._r8-om_frac) * eps**2._r8 * f_a**(3._r8 / bsw(c,j)) ) &


Suggested change

(1._r8-om_frac) * eps**2._r8 * f_a**(3._r8 / bsw(c,j)) ) &

(1._r8-om_frac) * eps*eps * f_a**(3._r8 / bsw(c,j)) ) &

swensosc added 9 commits March 4, 2026 09:28

wetland/methane updates

f2d2d1a

change vmax_oxid_unsat

9cf4f0e

Merge remote-tracking branch 'escomp/master' into wetland_update

a256125

change concentration adjustment

d87a6da

Merge remote-tracking branch 'escomp/master' into wetland_update

569071b

modify stream depth calculation

a227465

remove hard coded parameters

85b922c

cleanup

6f36cc6

Update mosart checkout to mosart1.1.13, matching .gitmodules

45d051e

swensosc mentioned this pull request Mar 26, 2026

CH4 tuning for CLM6 & WIEMIP #3843

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Merge remote-tracking branch 'escomp/master' into wetland_update

4676870

wwieder reviewed Mar 27, 2026

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slevis-lmwg requested changes Mar 27, 2026

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post-review cleanup

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ekluzek reviewed Mar 27, 2026

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swensosc added 2 commits March 27, 2026 13:13

add comment

0d7275d

add conditional to build namelist for prognostic finundated

83c6b14

slevis-lmwg assigned swensosc and slevis-lmwg Mar 27, 2026

slevis-lmwg added science Enhancement to or bug impacting science test: aux_clm Pass aux_clm suite before merging labels Mar 27, 2026

slevis-lmwg requested changes Mar 27, 2026

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cleanup

d57db36

	real(r8), parameter :: psi_fc = 3.4e3 ! matric potential at field capcity (mm)
	real(r8), parameter :: psi_fc = 3.4e3_r8 ! matric potential at field capcity (mm)

		if ( .not. readv ) call endrun(msg=trim(errCode)//trim(tString)//errMsg(sourcefile, __LINE__))
		params_inst%f_ch4=tempr

	character(len=32) :: subname='ch4_tran_surface_layers' ! subroutine name
	character(len=32) :: subname='ch4_tran' ! subroutine name

	(1._r8-om_frac) * eps*2._r8 f_a**(3._r8 / bsw(c,1)) ) &
	(1._r8-om_frac) * epseps f_a**(3._r8 / bsw(c,1)) ) &

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swensosc commented Mar 26, 2026

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swensosc commented Mar 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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swensosc commented Mar 27, 2026 •

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