How to compare the model outputs (e.g. leaf C, leaf N) with observations

[Paul]

Hello everyone, the CLM5 outputs the state variables for leaf C in three pools (LEAFC, LEAFC_STORAGE, and LEAFC_XFER), as well as for other tissues such as root or stem. The units of these outputs are 'gC/m^2'. I have two questions regarding the comparison of these data with observations:

1. Does the 'm^2' in 'gC/m^2' refer to grid area or leaf area? Additionally, observations are typically reported in units of 'mg/g'. How can I compare the model data with the observations?
2. Should I compare the observations with LEAFC alone or with the sum of the three pools?

Thanks!

 

[slevis]

1. gC/m2 in the model refers to land area, not leaf area. To compare to obs, you will need to convert units.
2. A quick search through the CTSM documentation led me here, where you will find answers to your questions:

2.20. Vegetation Phenology and Turnover — ctsm release-clm5.0 documentation

 

[Paul]

Thanks for the reply!

 

[wwieder]

Hi Paul, just one point of clarification here. If you're interested in comparing to something like SLA or LMA (which would have units as m2/gC , or the reverse mgC/ per leaf area), this is actually a PFT-specific parameter (or input) to the model. Then the model calculates its own leaf area index (ELAI in the model) based on allocation, phenology and SLA, which also generates leaf biomass (LEAFC) and litterfall fluxes.

Does this help at all, or just muddy the water?

 

[Paul]

Hi Wieder, sorry for the late reply. SLA should be an important parameter for unit conversion. And I found the input for "slatop" (specific leaf area at top of canopy) in the CLM code, which might be approximated as the SLA?

Thank you very much for the addition!

 

[slevis]

Yes, slatop may be an approximation of sla. It seems you could get a canopy-average sla from the ratio
TLAI / LEAFC
Does that sound right?

 

[wwieder]

slatop is on the parameter file, which may be easier to look at for individual PFTs.
Otherwise, Sam, your suggestion to TLAI/LEAFC would give canopy SLA in m2/gC