Question on soil moisture conversion

Added by Markus Mingel about 4 years ago

Hi all,

I would convert CMIP6 water content [kg m-2] to soil moisture fraction [m3 m-3]; all I need to do is divide the variable mrsol by the thickness of the layer in [mm]; this latter is retrieved from depth_bnds.
What I usually do is to split the layers and multiply by the thickness (I compute this in advance); I attach a sample file for testing:

cdo -splitlevel mrsol.nc TMP/soilm

depth_bnds =
0, 0.065,
0.065, 0.319,
0.319, 1.232,
1.232, 4.134,
4.134, 9.834 ;

thickness:
(0.065 - 0) * 1000 = 65 mm
(0.319 - 0.065) * 1000 = 254 mm
(1.232 - 0.319) * 1000 = 913 mm
(4.134 - 1.232) * 1000 = 2902 mm
(9.834 - 4.134) * 1000 = 5700 mm

cdo -divc,65.0 -setunit,'m3 m-3' TMP/soilm000.03.nc TMP/soilm1.nc
cdo -divc,254.0 -setunit,'m3 m-3' TMP/soilm000.19.nc TMP/soilm2.nc
cdo -divc,913.0 -setunit,'m3 m-3' TMP/soilm000.78.nc TMP/soilm3.nc
cdo -divc,2902.0 -setunit,'m3 m-3' TMP/soilm002.68.nc TMP/soilm4.nc
cdo -divc,5700.0 -setunit,'m3 m-3' TMP/soilm006.98.nc TMP/soilm5.nc

cdo merge TMP/soilm1.nc TMP/soilm2.nc TMP/soilm3.nc TMP/soilm4.nc TMP/soilm5.nc soilm.nc

I wonder if is possible to automatically do that without splitting the levels and computing into advance the thickness of each layer?

Thank you in advance for help!

Markus

mrsol.nc (1.46 MB) mrsol.nc

Replies (2)

RE: Question on soil moisture conversion - Added by Karin Meier-Fleischer about 4 years ago

Hi Marcus,

as far as I know there is no operator to do it for you, but a short shell script will do it.

#!/usr/bin/env ksh

mkdir -p tmp_mrsol
cdo -splitlevel mrsol.nc tmp_mrsol/soilm
files=$(ls tmp_mrsol/soilm*.nc)

for f in $files
do
    dbnds=$(ncdump -v depth_bnds $f | sed -e '1,/depth_bnds =/d' -e '$d' -e 's/ //g' -e 's/,/ /g' -e 's/;//g' | tr -d \\n)
    set -A bnds $dbnds
    nbnds=$(echo ${bnds[*]} | wc -w)
    echo "depth_bnds = ${bnds[*]}" 

    integer i=0, j=0
    for ((i=0; i<$nbnds; ++i))
    do
       j=$i+1
       a=${bnds[$j]}
       b=$(echo "scale=10; ${bnds[$i]}*1.0" | bc -l)
       thick=$(echo "scale=10; ($a-$b)*1000" | bc -l)
       echo "($i,$j):  a = $a  b = $b  (a - b) = $thick" 
       i=$i+1
    done

    cdo -divc,$thick -setunit,'m3 m-3' $f tmp_mrsol/tmp_${f##*/}.nc
done

cdo -O merge tmp_mrsol/tmp_soilm*.nc soilm.nc

To compare input file and computed output file:

cdo infon mrsol.nc
    -1 :       Date     Time   Level Gridsize    Miss :     Minimum        Mean     Maximum : Parameter name
     1 : 1975-01-01 06:00:00    0.03    73728   48857 :      0.0000      8.0742      49.707 : mrsol         
     2 : 1975-01-01 06:00:00    0.19    73728   48857 :      0.0000      34.425      196.41 : mrsol         
     3 : 1975-01-01 06:00:00    0.78    73728   48857 :      0.0000      105.50      754.97 : mrsol         
     4 : 1975-01-01 06:00:00    2.68    73728   48857 :      0.0000      185.63      2527.5 : mrsol         
     5 : 1975-01-01 06:00:00    6.98    73728   48857 :      0.0000      72.640      2650.5 : mrsol

cdo infon soilm.nc
    -1 :       Date     Time   Level Gridsize    Miss :     Minimum        Mean     Maximum : Parameter name
     1 : 1975-01-01 06:00:00    0.03    73728   48857 :      0.0000     0.12422     0.76473 : mrsol         
     2 : 1975-01-01 06:00:00    0.19    73728   48857 :      0.0000     0.13553     0.77329 : mrsol         
     3 : 1975-01-01 06:00:00    0.78    73728   48857 :      0.0000     0.11555     0.82692 : mrsol         
     4 : 1975-01-01 06:00:00    2.68    73728   48857 :      0.0000    0.063967     0.87096 : mrsol         
     5 : 1975-01-01 06:00:00    6.98    73728   48857 :      0.0000    0.012744     0.46500 : mrsol

-Karin

RE: Question on soil moisture conversion - Added by Markus Mingel about 4 years ago

Hi Karin,

thanks a lot, it works perfectly.
Markus

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