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TOPIC: Calculation wilting point / field capacity

Calculation wilting point / field capacity 1 year 2 months ago #2474

Dear all,

We are trying to calculate the soil wilting point and field capacity from the sand and clay fraction from HARMONIE/SURFEX, but I'm getting some strange results. The sand/clay fractions seem to be extracted from `PGD.fa` (I got the data in NetCDF format from KNMI), and I'm using the following equations to calculate the wilting point and field capacity (from surfex/SURFEX/mode_soil.F90):

WWILT_FUNC_2D = 0.15333-0.147*PSAND+0.33*PCLAY-0.102*(PCLAY**2)
WFC_FUNC_2D = 0.1537-0.1233*PSAND+0.2685*PCLAY**(1./3.)

The results don't look unreasonable, but the difference between field capacity and wilting point seems to be too low (see attachment).

Are we making a mistake somewhere in the conversion? The NetCDF file with clay/sand fraction is available here: www.dropbox.com/s/ccghezij5nq6z85/PGD_clay_sand.nc?dl=0

Python code we use:
import xarray as xr
scf = xr.open_dataset('data/PGD_clay_sand.nc')

pclay = scf['SFX.CLAY']
psand = scf['SFX.SAND']

theta_wp = 0.15333-0.147*psand+0.33*pclay-0.102*(pclay**2)
theta_fc = 0.1537-0.1233*psand+0.2685*pclay**(1/3)

Last Edit: 1 year 2 months ago by Bart van Stratum.
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