Seeking Detailed Information on CLM Model Parameters and Variable Interpretation

[yuezhouchen]

Hi all,

I wanted to reach out to the community for some assistance regarding the CLM (Community Land Model) parameters. Recently, I came across the clm5_params.c171117.nc file and found a lot of parameters within it. However, I noticed that the descriptions provided in the file are quite brief.

I am particularly interested in gaining more in-depth knowledge about these parameters and their impact on the CLM model. For instance, when I extracted a variable named "segment" from the parameter file and examined its values, I noticed they appeared in the form of 'b's', 'b'x', 'b'u'', etc. I'm uncertain about the meaning behind these expressions and would appreciate clarification.

If any of you have insights or suggestions on where I can find more detailed explanations or additional resources to understand these parameters better, please let me know. Your guidance and recommendations would be highly appreciated.

Thank you all for your time and support.

Best regards,
chen

 

[yuezhouchen]

Perhaps here, it might be different from what I had in mind, and it may take some time to understand.

2. CLM Technical Note — ctsm release-clm5.0 documentation

 

[oleson]

Yes, that is probably a good place to start. I can add that several of the code modules have a section where the parameters are read into the code. For example, in PhotosynthesisMod.F90, there is a readParams subroutine where parameters relevant to photosynthesis are read in, for example:

tString = "krmax"
call ncd_io(varname=trim(tString),data=temp1d, flag='read', ncid=ncid, readvar=readv)
if ( .not. readv ) call endrun(msg=trim(errCode)//trim(tString)//errMsg(sourcefile, __LINE__))
params_inst%krmax=temp1d

You can then search on params_inst%krmax in the code to find out where and how it is used and reconcile it with the equations in the tech note.
Another example are the parameters shared by biogeochemistry modules, found in CNSharedParamsMod.F90.

To answer your specific question, segment refers to the "segments" of the plant hydraulic scheme, i.e.,


segment =
"sunlit ",
"shaded ",
"xylem ",
"root " ;

Some of the plant hydraulic parameters have this extra dimension:

double kmax(segment, pft) ;
kmax:coordinates = "segment pftname" ;
kmax:units = "mm h2o (transpired)/mm h2o (water potential gradient)/sec" ;

I'm not sure which version of the model has "b's', 'b'x', 'b'u'', etc. "

 

[yuezhouchen]

Yes, that is probably a good place to start. I can add that several of the code modules have a section where the parameters are read into the code. For example, in PhotosynthesisMod.F90, there is a readParams subroutine where parameters relevant to photosynthesis are read in, for example:

tString = "krmax"
call ncd_io(varname=trim(tString),data=temp1d, flag='read', ncid=ncid, readvar=readv)
if ( .not. readv ) call endrun(msg=trim(errCode)//trim(tString)//errMsg(sourcefile, __LINE__))
params_inst%krmax=temp1d

You can then search on params_inst%krmax in the code to find out where and how it is used and reconcile it with the equations in the tech note.
Another example are the parameters shared by biogeochemistry modules, found in CNSharedParamsMod.F90.

To answer your specific question, segment refers to the "segments" of the plant hydraulic scheme, i.e.,


segment =
"sunlit ",
"shaded ",
"xylem ",
"root " ;

Some of the plant hydraulic parameters have this extra dimension:

double kmax(segment, pft) ;
kmax:coordinates = "segment pftname" ;
kmax:units = "mm h2o (transpired)/mm h2o (water potential gradient)/sec" ;

I'm not sure which version of the model has "b's', 'b'x', 'b'u'', etc. "

Thank you for your answer. it was very helpful to me. The previously mentioned " 'b's', 'b'u', 'b'n' " was a mistake on my part. I exported the variable data to an EXCEL spreadsheet, and since this is a char array, each cell contains a single letter. It was a comical oversight. I used ncdump to export the variable to a txt file and clarified its contents.