fix l bgc heat

[Eleanor Burke (eleanorgb)]

PR Summary

Updating l_bgc_heat to work with UM/and one layer soil carbon model

Sci/Tech Reviewer: Joe Clarke (@josephjclarke)
Code Reviewer: Erica Neininger (@ericaneininger)

https://github.com/MetOffice/um/pull/126

Code Quality Checklist

(Some checks are automatically carried out via the CI pipeline)

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• If editing rose-meta/jules-shared then have you supplied a linked UM and LFRic Apps PR?

UM only linked PR: https://github.com/MetOffice/um/pull/126

Testing

• I have tested this change locally, using the JULES rose-stem suite
• If shared files have been modified, I have run the UM and LFRic Apps rose stem suites
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (eg. kgo changes)
• I have added tests to cover new functionality as appropriate (eg. system tests, unit tests, etc.)

Im putting a series of changes in all of which I will protect with a rose stem test gong forwards

Test Suite Results - jules - l_bgc_heat/run2

Suite Information

Item	Value
Suite Name	l_bgc_heat/run2
Suite User	eleanor.burke
Workflow Start	2026-08-28T12:12:09
Groups Run	all

Dependency	Reference	Main Like
jules	eleanorgb/jules@126---fix-l_bgc_heat	False
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True

Task Information

✅ succeeded tasks - 676

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

Performance Impact

• Performance of the code has been considered and, if applicable, suitable performance measurements have been conducted

AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

Approvals

Please request all relevant approvals. See the CodeOwners.txt file for section owners.

Technical

• JULES Code Owner
• OpenMP
• River Routing
• Rose Stem
• Rose Metadata
• Upgrade Macros

Scientific

• Surface
• Hydrology
• Vegetation
• Veg3 RED Demography
• Biogeochemistry - approved by Eleanor Burke
• Biogenic fluxes
• Fire
• Lakes
• Evaluation
• Imogen

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

Please alert the code reviewer via a tag when you have approved the SR

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• CLA compliance has been confirmed
• Code quality standards have been met
• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[Copilot]

Pull request overview

This PR updates the biogeochemical soil heating option (l_bgc_heat) so it can be used in UM-JULES configurations and with the 1-layer soil carbon setup, primarily by aligning the respiration/heating logic with the soil-carbon layer dimension (dim_cslayer) and removing prior “standalone-only” gating.

Changes:

• Update soil_htc biogenic heating to use dim_cslayer (carbon-layer dimension) rather than nshyd (hydrology/soil moisture levels).
• Remove UM-side unavailability checks and standalone rose-meta constraints/warnings that prevented enabling l_bgc_heat.
• Add a new entry to CONTRIBUTORS.md.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/science/soil/soil_htc_jls_mod.F90	Switch biogenic heating loops/array shape to use dim_cslayer and add required module import/OpenMP shared var.
src/control/um/check_unavailable_options_mod.F90	Remove the UM runtime message that previously rejected l_bgc_heat.
src/control/shared/jules_soil_biogeochem_mod.F90	Relax configuration checks that previously required l_q10/l_layeredc for l_bgc_heat.
rose-meta/jules-standalone/HEAD/rose-meta.conf	Remove standalone metadata restriction and warning tied to UM and l_q10 when using l_bgc_heat.
CONTRIBUTORS.md	Add contributor entry.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[Maggie (maggiehendry)]

Changes look fine to me. I'd just like to check the logic. Thanks.

[Maggie (maggiehendry)]

Am I right in thinking that these changes allow l_bgc_heat to be used either with l_layeredC=.true. or l_layeredC=.false.

[Eleanor Burke (eleanorgb)]

This is correct

[Erica Neininger (ericaneininger)]

These changes look fine to me.

Please could you update to the head of main, and ensure that the rose-meta changes are up to date with the move of all UM metadata to this repository (see PR #155) - and therefore close the related UM PR as I believe it is no longer required - those changed should instead be made on this branch.

[Eleanor Burke (eleanorgb)]

These changes look fine to me.

Please could you update to the head of main, and ensure that the rose-meta changes are up to date with the move of all UM metadata to this repository (see PR #155) - and therefore close the related UM PR as I believe it is no longer required - those changed should instead be made on this branch.

I think Ive updated to head of the main?

[Erica Neininger (ericaneininger)]

These changes look fine to me.
Please could you update to the head of main, and ensure that the rose-meta changes are up to date with the move of all UM metadata to this repository (see PR #155) - and therefore close the related UM PR as I believe it is no longer required - those changed should instead be made on this branch.

I think Ive updated to head of the main?

It looks like you have done a merge, but something is not quite right - what you have done is rolled back the meta= tag on (some of?) the apps in rose-stem - they should all say vn8.2_t155, and some are now at the prior tag of vn8.2_t141.
The upgrade macro for #155 is also now missing?

[Erica Neininger (ericaneininger)]

Thanks for these changes.

Irritatingly, as a result of the change to jules-shared/jules-model-environment, I think you do now actually need to update the dependencies file in the UM, and provide an upgrade macro to un-ignore l_bgc_heat from UM apps.

Approving this PR, pending Maggie's code owner approval and the creation of a UM PR with an "empty" upgrade macro.