Historical configuration for CLM6

[wwieder]

In our meeting today there was discussion on creating land use time series for historical simulations with CLM6. We want to be able to run full historical simulations "out of the box" through 2022 (last year of CRUJRA inputa data). This will avoid anoying restarts in 2015 to continue historical simualtions. Most of the discussion was on the land use time series, but I think this also applies to datm.streams that we're reading in.

Regarding the landuse timeseries, we discussed several options:

1. Remake the landuse timeseries to cover 1850-2022 with existing CTSM5.2 historical datasets and SSP2-4.5.

• Note, this is where the continuous ssp extensions can also be set up for historical simulations with datm.streams

2. Create the landuse timeseries as above, but with the CTSM5.3 PR, CTSM5.3.0: New raw pft/lai/glc-behavior/soilcolor/fire datasets #2500
3. Create the landuse timeseries using the updated LUH2 data from TRENDY, which has been updated from the CMIP6 data
4. Wait for the official CMIP7 landuse data to come out, which will likely be the same as # 3.

Here are my questions:

• Quickest path forward would be option 1, we just need to remake the data that's already on hand. @slevis-lmwg thinks this could be done pretty efficiently before the summer code freeze.
• Options 3 & 4 will likely be what we want to use for the CESM3 release, but is it urgent to do these before the summer code freeze?
• If we ultimately want options 3/4, what is gained in the 5.3 work at all? Is it just the high res capabilities?

@lawrencepj1 and @dlawrenncar can you weigh in here on the best path forward.

[ekluzek]

@wwieder option 1 is already covered as we use the SSP2-4.5 landuae time series files for historical simulations.

[lawrencepj1]

Hi @wwieder

I think the idea for option 3 is that it will be very close to CMIP7 land use and consistent with the next version of Trendy to be run this summer so allows us to progress without waiting for CMIP7 which has a pretty open timeframe at the moment. Additionally this option has the updated PFT and CFT distributions which will be beneficial for the high resolution data.

Peter

[dlawrenncar]

I think that Options 3 / 4 are what we will need for the release. I don't think we expect big changes from what is in CTSM5.2, so I think it might be ok to just use what we are doing now (e.g., extending LUH2 with SSP2-4.5 to get to 2022) for any historical test simulations that are being done in land-only or coupled configurations. But, we should be pushing towards Option 3, superseded by Option 4 if beta CMIP forcing data becomes available. I don't think this is required by the code freeze. Changes from tuning will be much larger than changes due to these small land use forcing changes, but for the sake of simplicity, the earlier we can get option 3 in place, the better. But, it's not a code freeze deadline issue.

…

On Fri, May 31, 2024 at 10:27 AM Peter Lawrence ***@***.***> wrote: Hi @wwieder <https://github.com/wwieder> I think the idea for option 3 is that it will be very close to CMIP7 land use and consistent with the next version of Trendy to be run this summer so allows us to progress without waiting for CMIP7 which has a pretty open timeframe at the moment. Additionally this option has the updated PFT and CFT distributions which will be beneficial for the high resolution data. Peter — Reply to this email directly, view it on GitHub <#2570 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFABYVGGLWKHAA5G2JG3EBLZFCQHPAVCNFSM6AAAAABITAAB6CVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCNBSGYYDIOJQGE> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[wwieder]

From discussions at the CESM workshop it sounds like @dlawrenncar and @lawrencepj1 suggested migrating to CTSM5.3 datasets should happen concurrently with the switch to the TRENDY LULCC land use time series. This should also happen before we start trying to evaluate/calibrate historical simulations in CLM or CESM3. I'm still a bit uncertain on timing, this may not be critical before the July 31 deadline, but maybe should be soon thereafter?

[slevis-lmwg]

@slevis-lmwg @lawrencepj1 @samsrabin @ekluzek @linniahawkins discussed next steps for ctsm53.
@samsrabin took notes here:
https://docs.google.com/document/d/1-2LEjIhbs4j4NoythdLqdJ9A1pcNt4UJ_tyda2rrQWc

A PR documenting this work is already open: #2500