The land model in CCSM3 is the Community Land Model 4.0 (CLM4).
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).
Some near-modern simulations are able to use the present day (default) surface dataset pointed to in the build script (clm.buildnml.csh) :
e.g., set fsurdat = ‘surfdata_0.9x1.25_simyr1850_c091006.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.
Changing land ice
If your experiment requires a change in land ice, we provide a tool called convert_mksrf.F90 that will modify the default mksrf files to reflect land surface changes in glaciers, lakes/wetlands, and PFTs and produce new mksrf_glacier_myrun.nc, mksrf_lanwat_myrun.nc and mksrf_pft_myrun.nc files. The program requires a netcdf file containing your surface variables at 10min resolution. If you have added land ice over ocean grid cells (e.g., Fenno-Scandia, Hudson Bay) you will also need to create new coupler mapping files to reflect the new land cells.
Changing land cover
CLM4 does not require an initial condition file and can be initialized with arbitrary initialization and the surface dataset created from your mksrf datafiles [finidat = ‘ ‘]
You can also branch from an existing simulation, using clm2.r files to initialize your new experiment.
Note: CLM4 no longer uses clm.i files.
However, if you have changed your land cover in your new simulation (for example, if you have changed your land ice distribution), you will first need to create a new clm2.r file that conforms to your new land cover assignments. Creating a new clm2.r file is a two step process:
Set up and run a 5-day startup simulation with your new surface dataset and arbitrary initialization:
re-map the land properties from the original simulation clm2.r file, onto your new branch clm2.r file using interpinic.
/mypath/cesm1_0/models/lnd/clm/tools/interpinic % interpinic -i originalrun.clm2.r.0900-01-01-00000.nc -o my5dayrun.clm2.r.0001-02-01-00000.nc
The 5 day startup simulation will produce a new clm2.r file with landunit vector lengths consistent with the ice distribution in your new surface dataset, but different from the original experiment that you wish to branch from. Use the tool, interpinic, to re-map the spun-up data from the original simulation clm2.r file onto the new initial file created by the 5-day startup run.
The CLM4 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 CLM4 PFT you may need to edit this dataset. Please read the CLM4 documentation 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 CLM4 grid (the CLM4, CAM4 and CAM5 models typically use the same 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 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.csh.