Fire update May 2025

[lifang0209]

Description of changes

• Reduces fire count 99.6% above 2500 meters elevation based on GFED5 elevation bins of burned area, to eliminate overestimation of burning on Tibetan Plateau.
• Updates deforestation fire parameterization based on ctsm5.4 LU and GFED5 burned area.
• Fixes/improves comments

For now, also makes it so that crop fires don't happen if cropland is < 10% of the gridcell. However, this was only a kludge to avoid some mathematical weirdness with interpolation of agricultural peak burning month using average. This will be replaced by a more appropriate interpolation method with #3188, after which maybe remove 10% cropland threshold. However, that will make cropland burned area 10-30 Mha worse.

Specific notes

Contributors other than yourself, if any: None

CTSM Issues Fixed: None

Are answers expected to change (and if so in what way)? Yes. @lifang0209, can you please add a comment explaining the results before and after?

Any User Interface Changes (namelist or namelist defaults changes)?
Namelist defaults:

• defo_fire_precip_thresh_bet for CRU-JRA
• cli_scale for CRU-JRA and GSWP3
  Parameter file:
• rswf_max(3)
• rswf_min(3)
• fsr_pft and fd_pft, although these changes cancel each other out

Does this create a need to change or add documentation? Did you do so? No

Testing performed, if any:
@lifang0209, please add a comment explaining scientific testing.

Before merging:

• rimport new parameter file.
• aux_clm, expecting diffs only in li202[14]* fire methods. (2021 because of paramfile changes to rswf_min/max; 2024 due to those changes and others.)

[samsrabin]

Pretty simple and mostly looks good. Just some changes to request, which I can handle.

• defo_fire_precip_thresh_bet also needs to be changed, just for CRU-JRA. New value 3.0.
• Change cropfire_a1 to 0.32, even if we get rid of the 10% crop fraction threshold
• Change values on parameter file to match those in /glade/u/home/fangli/ctsm60_params.fire.crujra0530.nc:
  (1) rswf_max(3)=0.7d00
  (2) rswf_min(3)=0.35d00
  (3, 4) multiplying fsr_pft by 5 and dividing fd_pft by 5, based on FireAtlas and more reasonable, does not affect the results

[samsrabin]

Blocked by #3188.

[samsrabin]

This is unblocked; now waiting on @lifang0209 to change the code to avoid the crop fraction threshold now that #3188 is merged.

[lifang0209]

@samsrabin Hi Sam,
(1) Using the new abm raw data, the following comment could be removed
"! cropf_col(c) * col%wtgcell(c) > 0.1_r8 is added because fires are rare in
! gridcells with limited cropland coverage based on GFED5. Also, this helps to
! avoid abm (crop fire peak month) regridding error from 0.05 degree to lower resolution
! The condition could be removed if CLM supports the use of mode in abm inputs regridding"

(2) remove “.and. cropf_col(c) * col%wtgcell(c) > 0.1_r8 ” from the condition statement
(3) cropfire_a1 = 0.34d00

[samsrabin]

Great, thanks! Will do.

[samsrabin]

Blocked while we wait for the 5.4 update, since this depends on new surface datasets.

[wwieder]

We have the 5.4 branch. Can / should this PR get merged to the 5.4 branch so we can start evaluating fire results in coupled model tests?

[lifang0209]

Yes, I think it should be merged.

[samsrabin]

@wwieder @lifang0209 This is ready for testing! You can see the script I used to apply the paramfile changes here: /glade/work/samrabin/ctsm_ctsm6_li2024/tools/contrib/paramfile_changes/paramfile_chg_ctsm6_li2024.20250822.py.

[samsrabin]

Note that this will show a lot of diffs until the alpha-ctsm5.4.CMIP7 branch is brought up to date with ctsm5.3.071.

[samsrabin]

• Perform final approving review once (a) at least ctsm5.3.071 has been merged into alpha-ctsm5.4.CMIP7 and (b) the corresponding tag on that branch has been merged into here.

[wwieder]

I suggest this come in after the 5.4 tag is made, giving us a bit more time to generate initial conditions and evaluate historical fire results on top of the PPE115 parameter file that's being used in NCAR/LMWG_dev#116

[lifang0209]

@wwieder Hi Will, if the 5.4 tag uses CTSM5.4 surface and land use data, it‘s better to include the fire scheme updates. The updates include recalibration based on new abm (crop peak month) and land-use-based deforestation rate.

[samsrabin]

@ekluzek Should this be tag alpha-ctsm5.4.CMIP7.10.ctsm5.3.068?