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how does clm deal with modified surface and landuse data files

A

AndrewY

New Member
Hello everyone,

I'm running cesm (using the compset FHIST) with modified namelist variables fsurdat and flanduse_timeseries. However, I often ran into problems related to the landunit percentages (sometimes the problem would be "mismatch of input dimension"). So I have the following questions:

Say I have already modified the variable PCT_CROP in the surface data file to make specific grids into 100% of crops (or change the land cover types of specific grids from vegetation to others). Given the landuse data file also includes the same variable (i.e., PCT_CROP), I wonder how the model deals with the discrepancy in those values between the two data files? Will the model just discard the values (e.g., PCT_CROP, PCT_NAT_PFT) provided by the landuse data file over those land cover-changed grids? Does the run type (startup or branch) matter?

Thank you! Any help would be appreciated!
 
O

oleson

Keith Oleson
CSEG and Liaisons
Staff member
In a transient case such as FHIST, the variables on the surface dataset for the year that the surface dataset is for (1850) should have the same values as the corresponding year on the landuse file, otherwise, the model would/should throw an error.
For example, for a recent FHIST I've run, the surface dataset and landuse dataset are:

fsurdat = '/glade/p/cesmdata/cseg/inputdata/lnd/clm2/surfdata_map/release-clm5.0.18/surfdata_0.9x1.25_hist_16pfts_Irrig_CMIP6_simyr1850_c190214.nc'
flanduse_timeseries = '/glade/p/cesmdata/cseg/inputdata/lnd/clm2/surfdata_map/landuse.timeseries_0.9x1.25_hist_16pfts_Irrig_CMIP6_simyr1850-2015_c170824.nc'

So, the data on fsurdat for year 1850 must be the same as the data on flanduse_timeseries for year 1850 for the variables in common with both files.
For other years, the landunits are adjusted according to the data on the flanduse_timeseries file.
There is a good (hopefully) description of how this happens in the CLM Technical Note:

2.27. Transient Land Use and Land Cover Change — ctsm release-clm5.0 documentation

escomp.github.io
 
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