Near-modern climate simulations | Land

The land model in CCSM3 is the Community Land Model 3.0 (CLM3).  If you plan to make changes to the land surface (land ice or vegetation types distributions, etc.) you will need netCDF files with your input topography (10min and 1o resolutions) and vegetation (0.5 o resolution).

Surface dataset

Some near-modern simulations are able to use the present day (default) surface dataset pointed to in the build script (clm.bldnml_prestage.csh)and Section 6.3:

e.g., set fsurdat = ‘surface-data.128x064_atm.gx1v3_ocn.080101.nc’

However, if you have made changes to your land cover (e.g., by adding/removing land ice) or by changing vegetation, you will need to change the raw input datasets to reflect these changes and create a new surface dataset.

CLM3 creates a new surface dataset (e.g., surface_data_048x096.nc)  at runtime from seven mksrf files that contain ‘raw’ data on 0.5 o (e.g., mksrf_glacier.nc) or 1o lat/lon grids (e.g., mksrf_lanwat.nc).  The raw data include high-resolution maps of land cover (PFTs or plant functional types), soil color, soil texture, leaf/stem areas and heights (LAI), land water (lakes and wetlands), glaciers, and urban areas (Table 30).   At model runtime, CLM3 reads in the mksrf files and creates a new surface datasetin the run directory, under the land subdirectory. From this point forward in the model integration, the surface_data_resoln.nc is all that is required for CLM3/CCSM3 to function.

Hint: Change the generic name of the new surface dataset to something more descriptive by adding your case ID and date and placing the surface dataset in your $CASEROOT/SourceMods/src.clm/ directory for future reference.  Then point to your new surface dataset in clm.buildnml_prestage.csh:

          Example:  set fsurdat = ‘surface_data_LGM_64x128.091012.nc’

Quaternary modelers can often use the default CLM3 mksrf files.  However, some time periods may require modifications to the present day mksrf files to simulate land cover or vegetation change.  

If your simulation requires drastic revisions to the ‘raw’ mksrf files, Deep Time Section 4.3.2.1 describes a tool for deep time experiments where continental configurations are very different from modern, and/or little is known about land cover and soil distributions.

NOTE:  If you have lowered sea level and exposed new land along the continental shelf, CLM3 will automatically define that new land as ‘wetland’. To reassign these points to another PFT you will need to modify your mksrf_pft file using a nearest neighbor algorithm to fill in the new land points.  You will also need to define LAI, SAI, and soil color for these cells.

NOTE:  Modifying mksrf_pft.nc can be tricky and drastically changing vegetation may result in a climate signal that is larger than the forcing (e.g., solar) that you are trying to simulate.  

 

CLM forcing datasets

FilenameTypeDescriptionDetails
fsurdat netCDF CLM3 surface data file

The surface-data set is created at runtime using the raw (mksrf) datasets if fsurdat = ‘ ‘.  Once the surface-data file is created, you can point directly to your new surface dataset:  fsurdat = ‘surface-data_64x128_8.5ka.101011.nc’

finidat netCDF CLM3 initial condition file  If the modeler is using a CLM3 initial condition file, this variable points to that file. Otherwise, set finitdat= ‘ ‘, for arbitrary initialization.
pft-physiology ASCII PFT physiology specifications  Unless the pft-physiology file was modified, the default file/location may be used. Otherwise, specify the unique filename and location.
rdirc05 ASCII River transport model initial file The default name for the RTM initial condition file is rdirc.05. Near modern simulations may use the default rdirc file even if they have added land ice.

 

CLM3 raw datafiles (mksrf)

The mksrf (raw) datasets contain land use information on a 0.5o grid. When the model is configured, the configure script automatically points to present day mksrf files in the CLM3 namelist. If you are using modified mksrf files generated by paleo_mkraw or convert_mksrf, you must point to these new mksrf files in clm.buildnml_prestage.csh. Note that pointing to these file in the namelist DOES NOT guarantee their use. These files are only used if fsurdat= ‘ ‘. 

FilenameType    Description
mksrf_soicol_clm2.nc netCDF raw soil color
mksrf_lanwat.nc netCDF raw land water (lakes, wetlands)
mksrf_glacier.nc  netCDF raw glacier
mkrsf_urban.nc netCDF raw urban
mksrf_lai.nc netCDF raw leaf area index (LAI)
mksrf_pft.nc netCDF raw plant function types (PFTs)
mksrf_soitex.10levels.nc netCDF raw soil texture

 

PFT-physiology dataset

The CLM3 land model defines the physiology of each plant functional type (PFT) in an ASCII text file, called ‘pft-physiology’.  The default pft-physiology definitions are generally used for paleo experiments.  However, if you wish to change the characteristic of a specific CLM3 PFT you may need to edit this dataset. Please read the CLM3 documentation (Section 8.3.1) before altering this file and/or contact a CCSM paleo liaison for a consultation.

 

Runoff directional dataset (rdirc)

The River Transport Model (RTM) runs inside the land model on a fixed regular grid that is different from the parent CLM3 grid (the CLM3 and CAM3 models use the same grid, which for CCSM3, is a Gaussian grid). The runoff directional dataset required for RTM is an ASCII file containing latitude, longitude, and an integer value describing the vector (direction) for runoff flow at each RTM grid point. The integer values are numbered from 1 to 8: 1=N, 2=NE (45o), 3=E (90o), etc.    See Section 4.3.4 for complete vector directions and integer labels.  Most near-modern experiments are able to use the default runoff directional dataset (rdirc.05) pointed to in clm.buildnml_prestage.csh.