Soil Moisture Data Set

This file defines the target values which are prescribed in CLM. It is a netCDF file and needs to have the variables SOILICE and SOILLIQ on it (even if you only prescribe SOILLIQ). The variables are not in the usual lat/ lon format (named 4D) but in an indexed format (named 3D). The data is obtained from a reference simulation of CLM. The file must have 365 (12) time steps on it to prescribe SM daily (monthly) data.

Obtain SM Data Set from CLM

CLM can directly output the needed 3D soil moisture fields. Assume you want to output daily 4D files in history tape 2 and daily 3D fields in history tape 3, you have to add the following lines to user_nl_clm:

# daily SM, lat, lon grid:
hist_fincl2 = 'SOILICE', 'SOILLIQ'
# daily SM, column form
hist_fincl3 = 'SOILLIQ','SOILICE'
hist_nhtfrq = 0, -24, -24
hist_mfilt = 1, 365, 365
# conversion to lat/ lon format?
hist_dov2xy = .true., .true., .false.

Convert 4D to 3D

If you only have the SM forcing file in 4D format it is possible to convert it to a 3D file. A small python script that shows how to do this is given in the repository:

It translates the lat/ lon information to index information. This requires one 3D file with the used set up (create it as in Obtain SM Data Set from CLM).

Regional Forcing

  • if you set SOILLIQ or SOILICE to -1 at a gridpoint/ level, SOILLIQ and SOILICE are calculated interactively at this point
  • this can be used to prescribe SM only regionally
  • or at certain depths only


to prescribe SM only at certain time days of the year will only work if you use (1) daily data and (2) set