Help needed with Trendy25 CLM-FATES results

[kjetilaas]

I am running the Trendy 2025 with CLM-FATES (NorESM checkout). See run scripts here:
https://github.com/kjetilaas/Trendy_2025_scripts

I have started processing the results using scripts in this repo:
https://github.com/[kjetilaas/Trendy25_post_process](https://github.com/kjetilaas/Trendy25_post_process)

But I run into a couple of issues/questions:

• How do I correctly calculate NBP from the output? (I have tried using FCO2, that doesn't seem to be correct)
• The simulations show some strange, sudden drops in Carbon pools, even for S0 (reference simulation). I have tracked this down to wood harvest, but I think this deserves further attention
• S3 (all forcing) has, as far as I can see, a positive NBP (and change in all carbon stocks), sometimes even larger than S2 (all forcing - LUC). This seems odd to me

Figures will follow soon

[kjetilaas]

First, here is the NBP calculated from "FATES_NEP" +"FATES_SEEDS_IN_EXTERN_EL" - "FATES_GRAZING" - "FATES_FIRE_CLOSS" - "TOT_WOODPRODC_LOSS" (corrected for different area.
And NBP calculated from FCO2 (converted to C instead of CO2 and changed sign):

They match well, except for an offset in FCO2.

This is not matched in the change in carbon pools:

[kjetilaas]

I am still not convinced that I have the right calculation for NBP, as the total NBP does not exactly match the change in carbon pools (here for S0), indicating that I am either missing a carbon pool or missing/double counting a flux:
Total Carbon change over timeseries:-2.775146484375 PgC
Change in TOTSOMC: -2.811863660812378 PgC
Change in FATES_VEGC: -0.061035510152578354 PgC
Change in PROD10C: 0.0104553597047925 PgC
Change in PROD100C: -0.04574562981724739 PgC
Change in FATES_LITTER_AG_CWD_EL: -0.8973209857940674 PgC
Change in FATES_LITTER_AG_FINE_EL: -0.264654278755188 PgC
Change in FATES_LITTER_BG_CWD_EL: 0.2796761989593506 PgC
Change in FATES_LITTER_BG_FINE_EL: 1.0154200792312622 PgC

Total NBP over timeseries for S0: -5.8944525718688965 PgC
Total FATES_NEP over timeseries for S0: 280.5501708984375 PgC
Total FATES_SEEDS_IN_EXTERN_EL over timeseries for S0: 39.78044128417969 PgC
Total FATES_GRAZING over timeseries for S0: 2.7412548065185547 PgC
Total FATES_FIRE_CLOSS over timeseries for S0: 288.2197265625 PgC
Total TOT_WOODPRODC_LOSS over timeseries for S0: 35.264095306396484 PgC

[rosiealice]

I'm not sure how you can tell that they don't match the carbon pools from the latter figure?

[rosiealice]

(it is good that FCO2 matches NBP at least...) Could you plot the difference between them so we can see how exact the fit it?

[kjetilaas]

Sorry, I was being unclear about FCO2 and NBP. The variability matches, but FCO2 has an offset of about 1.3 PgC/yr, which means the total carbon should grow by about 200-300 PgC over this period.

[rosiealice]

Noting that NorESM-FATES is not including the external seed rain in the NBP calculations.