Is `f - baf_crop` necessary in fire calculations for `is_cwd`?

[slevis-lmwg]

From looking at this with @wwieder and @klindsay28 on 2022/11/02 in the context of spinning up ctsm bgc with Newton-Krylov...

Why not use f rather than f - baf_crop with is_cwd in the following?

CNFireBaseMod.F90

f = farea_burned(c)
do j = 1, nlevdecomp
           ! carbon fluxes
           do l = 1, ndecomp_pools
              if ( is_litter(l) ) then
                 m_decomp_cpools_to_fire_vr(c,j,l) = decomp_cpools_vr(c,j,l) * f * &
                      cmb_cmplt_fact_litter
              end if
              if ( is_cwd(l) ) then
                 m_decomp_cpools_to_fire_vr(c,j,l) = decomp_cpools_vr(c,j,l) * &
                      (f-baf_crop(c)) * cmb_cmplt_fact_cwd
              end if
           end do

and similarly in the nitrogen loop.

Reasoning:

• Currently crops shouldn't generate cwd, so is_cwd should occur only when baf_crop = 0.
• Even if crops generated cwd (e.g. simulating orchards), why handle litter and cwd differently?
• Crop and non-crop veg. should not coexist in a column (pls correct my assumption if I'm wrong), so I would expect baf_crop = f in crop columns and baf_crop = 0 in non-crop columns.

I will share this question with Fang Li for clarification.

[slevis-lmwg]

Fang responded that this was done for the generic crops, which could coexist in a column with non-crop pfts depending on user-defined settings. If we still permit generic crops and non-crop pfts coexisting in a column, then Fang wants us to keep the code as written.

I believe the ctsm defaults to create_crop_landunit = .true., so we can assume baf_crop = 0 for the purposes of a Newton-Krylov spin-up. However, the ctsm code should remain as written as long as create_crop_landunit = .false. is an option.

[wwieder]

Thanks for following up with Fang on this @slevisconsulting. Can you make sure Keith Lindsay keeps this in the preconditioner for the N-K solver.

[wwieder]

Now I see @klindsay28 is already on the thread! I'll close this issue with a won't fix label

[ekluzek]

@slevisconsulting FYI we currently only allow create_crop_landunit=FALSE for FATES. But, we actually want to change this option so it's turned on all the time including for FATES.