Change the use of "potential vegetation" control variables in FATES? It's confusing with the CTSM usage of the term...

[ekluzek]

In CTSM the use of "potential vegetation" is used pretty synonymously with "recent Paleo", "no Anthro", or "land use off". In FATES it's used in the sense of leaving vegetation as primary land cover. I find the use of the same term in different ways to be confusing personally.

For example in CTSM in namelist_definition_ctsm.xml you have this statement:

A sim_year of PtVg refers to the Potential Vegetation dataset, that doesn't include human influences

namelist defaults has this:

Potential vegetation land use dataset, crop is off, and zeroed, all areas are natural vegetation without human disturbance

There's similar statements in the surface dataset generation tools

Within the FATES repository I only find these references:

biogeochem/FatesLandUseChangeMod.F90:    ! if we are using potential veg only, then keep all transitions equal to zero.
main/FatesInterfaceTypesMod.F90:   integer, public :: hlm_use_potentialveg          ! flag to signal whether or not to use potential vegetation only
main/FatesRestartInterfaceMod.F90:             ! can't go back into potential vegetation mode, it is a one-way thing.

I suggest the use in these files (and the PVT system test in CTSM) be changed to something that says something to the effect of all primary land rather than potential vegetation.

This discussion started in CTSM here:

https://github.com/ESCOMP/CTSM/pull/2898/files/b4415079927843cb752d2d6e6131c96c406f20a7#r1870145028

[ekluzek]

My suggestion is that:

hlm_use_potentialveg

change to:

hlm_use_all_primary_land

and the comments around them that say "potential veg" use "primary land". Similar changes would happen in CTSM for the PVT system test.

I can't comment on if there are changes that should happen to ELM, although it seems unlikely that ELM has a Paleo mode? NorESM does do Paleo work, but they stay pretty close to CTSM, so likely wouldn't have to do any changes themselves. So I think the change would only happen in FATES and then CTSM.

[wwieder]

@ckoven and @rosiealice I wonder if you can chime in here?

[rgknox]

In the FATES SE meeting there was agreement that the proposed change is a good one. We would like to tackle this "as time allows" and make sure that both sides (ctsm/fates) of the code are updated at the same time (to avoid confusion).

[ekluzek]

That sounds great to me. Thanks for talking it through. I'll turn the proposal into an issue.