Allow the land fraction to be flipped

[Dan Copsey (DanCopsey)]

PR Summary

Allow the land fraction field (once read in from ancillary file) to be flipped so that the data is south to north to be consistent with the other ancillary fields.

Sci/Tech Reviewer: Maggie (@maggiehendry)
Code Reviewer: Pierre Siddall (@Pierre-siddall)

When I put in #89 I added land fractions into the rivers-standalone part of JULES to be read in from an ancillary file. However if the other input fields (from ancillary files) are flipped to be running from south to north (using the remap_ancil function) then the land fraction field gets missed out and remains north to south. This makes an inconsistency in the data and the model fails. This change fixes this by adding in the call to remap_ancil for the land fraction.

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
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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.)

trac.log

Test Suite Results - jules - jules_fix_river_land_fractions/run1

Suite Information

Item	Value
Suite Name	jules_fix_river_land_fractions/run1
Suite User	dan.copsey
Workflow Start	2026-08-21T16:12:52
Groups Run	all

Dependency	Reference	Main Like
jules	DanCopsey/jules@fix_river_land_fractions	False
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True

Task Information

✅ succeeded tasks - 676

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Performance Impact

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Documentation

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Approvals

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Technical

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

Scientific

• Surface
• Hydrology
• Vegetation
• Veg3 RED Demography
• Biogeochemistry
• Biogenic fluxes
• Fire
• Lakes
• Evaluation
• Imogen

Sci/Tech Review

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• Sufficient testing has been completed

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

Code Review

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• Security considerations have been addressed
• Performance impact is acceptable

[Maggie (maggiehendry)]

I can't see anything wrong with the code change. I was about to say that LFRic coupled Rose stem test needs to be run, but the Rose stem test there has l_use_land_fraction=.false.. You should probably still run it though and add it to the PR as it does use the Rivers-standalone code which has been changed here.

[Pierre Siddall (Pierre-siddall)]

Thanks Dan Copsey (@DanCopsey), as this is a relatively simple change which calls an ancillary remapping this looks good to head into testing to me.