ctsm5.3.081

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Tag name: ctsm5.3.081
Originator(s): erik (Erik Kluzek,UCAR/TSS,303-497-1326)
Date: Wed 22 Oct 2025 05:31:52 PM MDT
One-line Summary: Change defaults for when Carbon isotopes are turned on, and turn on irrigate for Sp/Bgc cases for clm6_0 historical transient cases

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

Only turn C13/C14 for clm6_0 and BGC, and also require the DATM forcing to be CRUJRA2024 or CAM7 and for the historical period. So for example SSP compsets won't have C13/C14 on, single point compsets won't, or for using older forcing (like CAM6, or GSWP3v1, Qian, or CRUv7). Also whenever use_c13 or use_c14 is on turn on the corresponding time series file.

Also change default for irrigate to on for historical SP/BGC cases.


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

Does this tag change answers significantly for any of the following physics configurations?
(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 #3527 -- irrigation settings for control vs historical cases
Fixes #3551 -- Turn on relevent Carbon isotope time-series when use_c13/c14 is on
Some work on #3346 -- CMIP7 Carbon isotope data

Notes of particular relevance for users
---------------------------------------

Caveats for users (e.g., need to interpolate initial conditions):
This just changes the defaults for when Carbon isotopes are turned on, to make it less often
Users can still turn it on by hand for the cases that they want.

Changes made to namelist defaults (e.g., changed parameter values):
Carbon isotope timeseries files are turned on whenever use_c13/use_c14 is turned on so it uses
the historical
Turn irrigate on for clm6_0 historical
Carbon isotopes only turned on by default for clm6_0 when CRUJRA2024 or CAM7 forcing is used
and only for historical cases and not SSP's

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 (differences in namelists are all as expected)

python testing (if python code has changed; see instructions in python/README.md; document testing done):

derecho - PASS

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: previous


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

Changes answers relative to baseline: HistClm60 compsets and tests with the ciso testmod

Summarize any changes to answers, i.e.,
- what code configurations: HistClm60Sp/HistClm60Bgc now with irriage on
cases with use_c13/use_c14 now have c13/c14 isotope timeseries files on
- what platforms/compilers: all
- nature of change (roundoff; larger than roundoff/same climate; new climate):
Carbon Isotopes -- are diagnostic and only change fields on history files
Cases that now have C13/C14 isotopes on now use timeseries files rather
than the default pre-industrial so change answers for C13/C14 fields
Irrigate turned on for HistClm60Bgc/HistClm60Sp compsets will change answers

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

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

https://github.com/ESCOMP/CTSM/pull/3549

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