ctsm5.4.018

[CTSM Gatekeeper]

*** RESPONSES TO THIS EMAIL WILL NOT BE READ ***
===============================================================
Tag name: ctsm5.4.018
Originator(s): erik (Erik Kluzek,UCAR/TSS,303-497-1326)
Date: Thu Feb 12 11:28:51 AM MST 2026
One-line Summary: Quick fix so that we can use Nitrogen Deposition sent from the ATM model

Purpose and description of changes
----------------------------------

Add the ndep_inparm namelist to drv_flds_in, so that CTSM can turn on ndep from the ATM model. Also turn on using the ndep from the ATM model for the cam LndTuningMode testmods. And make sure ndep comes from CAM when we are coupled to CAM.

Significant changes to scientifically-supported configurations
--------------------------------------------------------------

Does this tag change answers significantly for any of the following physics configurations? No
(Details of any changes will be given in the "Answer changes" section below.)

[Put an [X] in the box for any configuration with significant answer changes.]

[ ] clm6_0

[ ] clm5_0

[ ] ctsm5_0-nwp

[ ] clm4_5


Bugs fixed
----------

List of CTSM issues fixed (include CTSM Issue # and description) [one per line]:
Fixes Add ndep_inparm namelist to drv_flds_in #3742
Fixes When coupled to CAM, ndep is still read in from CTSM rather than using what CAM is sending #3737
Fixes Ndep from ATM is now hard coded to 2 fields #3743
Fixes Have testmods with cam LndTuningMode use ndep from ATM #3744
Fixes Add CLM_NDEP_FROM_CPL XML variable #3747
Fixes Difference between ndep from CTSM streams and from DATM is significant #3748
Some work on Move settings from use_cases to namelist_defaults #605

Notes of particular relevance for users
---------------------------------------
Caveats for users (e.g., need to interpolate initial conditions):
Now you can trigger whether Nitrogen Deposition is coming from the ATM model or read inside of CTSM
(before it was ALWAYS read in)
This only matters for Bgc or BgcCrop compsets
You can see if ndep is coming from ATM or CTSM by doing this in your case:
./xmlquery CLM_NDEP_FROM_CPL
# (will be TRUE if coming from either DATM or CAM, FALSE if read internally in CTSM
grep ndep CaseDocs/*
# If the above is FALSE for an I compset you'll see matches in: datm_in and lnd_in
# If the above is TRUE when coupled to CAM you'll see matches in: atm_in and drv_flds_in
# (and in lnd_in, but just for the empty namelist: &ndepdyn_nml)

The lnd.log file also will explicitly say whether ndep is coming from ATM or read by CTSM

Changes to CTSM's user interface (e.g., new/renamed XML or namelist variables):
New XML variable: CLM_NDEP_FROM_CPL
For I compsets this is set to FALSE, but when coupled to CAM it's set to TRUE

Changes made to namelist defaults (e.g., changed parameter values):
None from the user perspective, unless you try to run with CLM_NML_USE_CASE==UNSET

Changes to documentation:
Updated notes on ndep

Notes of particular relevance for developers:
---------------------------------------------

Caveats for developers (e.g., code that is duplicated that requires double maintenance):
Settings for ndep moved from the use_case files to namelist_defaults_ctsm
ndep_list added to namelist_definition_drv_flds.xml

Changes to tests or testing:
clm*cam*LndTuningMode testmods changed to have ndep come from the ATM model (so DATM)
build-namelist tester updated to accommodate the addition of CLM_NDEP_FROM_CPL


Testing summary: regular
----------------

[PASS means all tests PASS; OK means tests PASS other than expected fails.]

build-namelist tests (if CLMBuildNamelist.pm has changed):

derecho - OK (some changes relative to ctsm5.4.017)

regular tests (aux_clm: https://github.com/ESCOMP/CTSM/wiki/System-Testing-Guide#pre-merge-system-testing):

derecho ----- OK
izumi ------- OK

If the tag used for baseline comparisons was NOT the previous tag, note that here:


Answer changes
--------------

Changes answers relative to baseline: yes (just when coupled to CAM or the CAM LndTuningMode testmods are used)

Summarize any changes to answers, i.e.,
- what code configurations: Only BGC cases for when Coupled to CAM / CAM LND_TUNING_MODE
- what platforms/compilers: All
- nature of change: same climate, changes Nitrogen deposition

We didn't run simulations but as the change to ndep is a normalized RMS of 1.e-4 we felt it should be OK

Other details
-------------

Pull Requests that document the changes (include PR ids):
(https://github.com/ESCOMP/ctsm/pull)

#3745 -- allows ndep to come from ATM model

===============================================================
===============================================================