Question about stem area index in CLM5.0

[Qi Qi]

Hi, everyone. I'm trying to do some experiments based on the changes on the stem area index (SAI/Ls). I noticed that in the document of CLM5.0 the stem area index was described as ''Prescribed plant functional type (PFT) stem area index is derived from PFT leaf area index phenology combined with the methods of Zeng et al. (2002)'.
However, the stem area index in the Zeng et al. (2002) is set to a minimum value of 1 to most plant functional types, which is inconsistent with the Monthly_SAI output in CLM5.0. It seems that the SAI in CLM5.0 is generated after the normalization but I could not find the eassy to clarify this assumption. Is there any supporting information about this topic?
Many thanks!

Zeng, X., Shaikh, M., Dai, Y., Dickinson, R.E., Myneni, R., 2002. Coupling of the Common Land Model to the NCAR Community Climate Model. J. Climate 15, 1832–1854. Coupling of the Common Land Model to the NCAR Community Climate Model

 

[slevis]

I searched in the CLM5 Technical Note and found this section talking about the stem area:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

Searching on that page for the string "stem" I found two possible explanations for values lower than expected:
1) "The leaf and stem area indices are adjusted for vertical burying by snow" shown in history fields ELAI and ESAI (instead of TLAI and TSAI).
2) "Prescribed PFT stem area index is derived from PFT leaf area index phenology combined with the methods of Zeng et al. (2002)." I can't tell you offhand the effect of phenology, but it may explain the lower values than expected. You may find an answer in the Phenology section of the Technical Note or you could look through the code.

Also, if you looked at grid-cell averaged TSAI or ESAI in the model output, then you may be averaging parts of the grid cell with no (or lower) stem area.

 

[Qi Qi]

I searched in the CLM5 Technical Note and found this section talking about the stem area:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

Searching on that page for the string "stem" I found two possible explanations for values lower than expected:
1) "The leaf and stem area indices are adjusted for vertical burying by snow" shown in history fields ELAI and ESAI (instead of TLAI and TSAI).
2) "Prescribed PFT stem area index is derived from PFT leaf area index phenology combined with the methods of Zeng et al. (2002)." I can't tell you offhand the effect of phenology, but it may explain the lower values than expected. You may find an answer in the Phenology section of the Technical Note or you could look through the code.

Also, if you looked at grid-cell averaged TSAI or ESAI in the model output, then you may be averaging parts of the grid cell with no (or lower) stem area.

Thanks for your reply!
I would check the code and the technical note more detailedly.

 

[praghav]

Hi, everyone. I'm trying to do some experiments based on the changes on the stem area index (SAI/Ls). I noticed that in the document of CLM5.0 the stem area index was described as ''Prescribed plant functional type (PFT) stem area index is derived from PFT leaf area index phenology combined with the methods of Zeng et al. (2002)'.
However, the stem area index in the Zeng et al. (2002) is set to a minimum value of 1 to most plant functional types, which is inconsistent with the Monthly_SAI output in CLM5.0. It seems that the SAI in CLM5.0 is generated after the normalization but I could not find the eassy to clarify this assumption. Is there any supporting information about this topic?
Many thanks!

Zeng, X., Shaikh, M., Dai, Y., Dickinson, R.E., Myneni, R., 2002. Coupling of the Common Land Model to the NCAR Community Climate Model. J. Climate 15, 1832–1854. Coupling of the Common Land Model to the NCAR Community Climate Model

Hi, Did you find the solution for this? I want to know how to calculate steam area index from leaf area index for a given PFT?

 

[slevis]

You will find that the model outputs both the leaf and the stem area index. If you prefer to calculate your own value of stem area index from the leaf area index, then you could try to replicate the model's calculation by following the documentation and the code. Or (sorry it's not clear to me) maybe you wish to use a different formulation than the clm formulation.

 

[praghav]

I am using the multilayer canopy version of the CLM model available at GitHub - gbonan/CLM-ml_v1: CLM-ml_v1 source code. This model requires leaf area index (LAI) and stem area index (SAI) as inputs at every model timestep. I will be running the model across AmeriFlux sites and plan to obtain LAI from sources like MODIS. My question is: Is there a way to calculate SAI from LAI? If so, can you please pinpoint the exact calculation in the model code? I have been unable to locate this in the model's source code.

 

[slevis]

"git grep sai"
or the somewhat more cumbersome
"grep sai *F90"
should lead you to the right place in the clm code.
From a quick look I got to src/biogeochem/CNVegStructUpdateMod.F90.

It may not be as simple as you may expect, so don't be surprised if it's not a single line of code. The CLM Technical Note also explains what is in the code:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

If you find that the clm solution does not work for you, then you may need to search the literature or internet for a simple conversion from lai to sai.