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The land component of CESM1.x is the Community Land Model, version 4.0 (CLM4). The CLM4 requires a surface dataset that defines the spatial distribution of vegetation, surface water, and land ice. This surface dataset is created offline, using CLM tools and the set of 'raw' datafiles, most of which are at 0.5deg resolution, that define the spatial distribution of vegetation types (PFT), inland lakes, and land ice data.
e.g., set fsurdat = ‘surfdata_0.9x1.25_simyr1850_c091006.nc’
Some near-modern simulations are able to use the present day (default) surface dataset. However, if you want to make changes to your land cover (e.g., by adding/removing land ice or by changing vegetation), you need to create a new surface dataset to reflect these changes. The surface dataset requires 'raw' data at 0.5 degree grid resolution netCDF files called 'mksrf' files. These data reflect the spatial distribution of vegetation types (PFT), inland lakes, and land ice data for the land model.
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 and/or 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 change to the land/sea mask.
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 restart from an existing simulation, using clm2.r files to initialize your new experiment.
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 the new land cover assignments in your modified surface datafile. Creating a new clm2.r file is a two step process. Step 1: Run a short (e.g., 5 day) startup simulation with arbitrary initial conditions and your new surface dataset. The 5 day simulation will produce a restart file that is consistent with the ice distribution in your new surface dataset, which is different from the original experiment that you wish to branch from. Use the tool, interpinic, to re-map the restart data from the original simulation to the new restart file created by the 5-day run.
Set up and run a 5-day startup simulation with your new surface dataset and arbitrary initialization to create a CLM restart file consistent with your new surface dataset.
finidat = ‘ ‘
fsurdat = '/mypath/surfdata_RESOLN_myrun.nc'
Map the data from the original restart file (original.clm.r.nc), onto the newly created restart file (my5day.clm.r.nc) using the tool interpinic, which is included with the CESM1 release.
% interpinic -i original.clm.r.nc -o my5day.clm.r.nc
Rename the newly remapped file to reflect its history.
% mv my5day.clm.r.nc original.clm.r.IP.nc (IP ~= interpinic)
NOTE: CLM4 may not allow you to specify both a surface dataset and finidat in user_nl_clm. If you get an error when running preview_namelist, then comment out the finidat line in user_nl_clm, and edit Buildconf/clm.buildnml.csh to point explicitly to your new file:
fsurdata = '/mypath/surfdata_RESOLN_myrun.nc'
finidat = '/mypath/original.clm.r.IP.nc'
start_file = '/mypath/original.clm.r.IP.nc'
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.
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.