# 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: clm_col_to_xy_example.py.

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

Warning

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