WHAM-INFERNO integration

[Oli Perkins (OliPerkins1987)]

PR Summary

Sci/Tech Reviewer: Eddy Robertson
Code Reviewer: Sam Clarke-Green (@t00sa)

PR Summary

This pull request summarises changes to the INFERNO fire module made in order to couple it with the WHAM model of human fire use and management. This improves INFERNO's performance significantly.

Evaluation of the model can be found here (in submission).
Evaluation_19_11_2025.docx

The full overview of WHAM! and the structure of its coupling is described in these three papers:

Model description: https://gmd.copernicus.org/articles/17/3993/2024/
Prototype coupling and calibration: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024EF004770
Future model runs: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3728/

An additional paper, detailing the online coupling is close to submission. Supporting files for that paper [including an R-based mockup of the fireline intensity algorithm] are available here: https://zenodo.org/records/18328879.

Although this PR allows WHAM! to be coupled with JULES in a dynamic way, it is not a full tight coupling (yet). Rather, outputs from the WHAM! model are passed as ancillaries. These are then updated in line with the changing distribution of plant functional types in JULES.

There are three fundamental changes made to the code.

1. The first (ignitions) is toggled using a new ignitions mode
2. The second (managed fire) is on a new switch "l_inferno_wham"
3. The third (fire line intensity) is able to run with / without WHAM!. It is set using a new "fire_mortality_method" integer that maintains current functionality.

1) Ignitions mode
A new ignitions mode is added (ignitions_mode == 4). This specifies that ignitions, or unmanaged fires, are taken from WHAM! outputs. These are the sum of accidental anthropogenic fires, arson (fire use as a weapon under land use conflict) and escaped fires - managed fires that grow out of control. Importantly, ignitions from WHAM! take account of the seasonality of human fire use: i.e. they vary monthly, rather than being uniform across the calendar year.
This also incorporates WHAM! projections of fire suppression (i.e. fire fighting).

2) Managed fire
As much as 50% of global burned area is generated by small anthropogenic fires, typically used in livestock farming and for hunting/gathering in savanna ecosystems. WHAM! adds these into the model. Setting l_inferno_wham to True switches this functionality on.

In addition, it also adds the use of road density to adjust mean fire size. This is a simple representation of fragmentation that should increase fire size & burned area in remote regions, whilst reducing it where there is widespread human activity.
Managed fire use varies month to month in line with WHAM!'s projection of fire use seasonality. (as with ignitions).
Human fire use for fire risk reduction (i.e. prescribed fire or cultural burning) changes dynamically with tree cover. See, it is lower in wet tropical forests than open savannas. This is updated dynamically based on the PFT distribution at each time step.

3) Fireline intensity
Work by Olivia Haas (https://iopscience.iop.org/article/10.1088/1748-9326/ac6a69) has demonstrated that fire intensity (Watts emitted per m2 burned) has different drivers to burned area.
Fire intensity is closely related to vegetation mortality. Therefore, a new intensity algorithm was developed that captures the spatio-temporal variation in mortality. This replaces the current parameterisation of mortality as the product of burned area and a scalar value per PFT.

A new variable "fire_mortality_method" is defined with three levels:

1=The original mortality method (per Burton 2019)
2=The Burton method adjusted for saturation moisture. This provides a boundary condition around tropical forests. Too much mortality in tropical forests has been an issue in INFERNO.
3=The new fireline intensity algorithm. I have added a supplementary file that shows the relationships used in this. Important to note is that this can be run with / without WHAM. So, setting fire_mortality_method = 3 & l_inferno_wham = .false. will replace WHAM! inputs into the intensity algorithm with a function of population density.

SI1_Intensity_Algorithm_15122025.docx

Code Quality Checklist

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

• [x ] I have performed a self-review of my own code
• [x ] My code follows the project's style guidelines
• [x ] Comments have been included that aid undertanding 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 PR?

Testing

• [NB - I am unable to do this because the rose stem does not run properly on JASMIN at the moment ] 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

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

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Documentation

• Where appropriate I have updated documentation related to this change and
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[Jenny Hickson (jennyhickson)]

Hi Oli,

We have github actions that try and monitor the status of pull requests based on the values of SciTech Review and Code Review in the pull request template. Please can you choose one person as the assigned Science Reviewer and put their github user ID rather than name in the form? You're welcome to request a review from the second person as well.

[Oli Perkins (OliPerkins1987)]

Hi Oli,

We have github actions that try and monitor the status of pull requests based on the values of SciTech Review and Code Review in the pull request template. Please can you choose one person as the assigned Science Reviewer and put their github user ID rather than name in the form? You're welcome to request a review from the second person as well.

Thanks - have emailed Eddy to ask what his GitHub Id is. OP

[Oli Perkins (OliPerkins1987)]

Hello,

Please could you advise what the umdp3 fixer is, where I can find documentation and whether it can be run on JASMIN? If not, I have no way of running it.

All best

Ol