Calculate Evapotranspiration (ET) and Soil Moisture & Adding Variables to NetCDF File

[ah828]

Hello, I am a new user and so these questions might be naïve.

I ran the I2000Clm50BgcCrop (2000_DATM%GSWP3v1_CLM50%BGC-CROP_SICE_SOCN_MOSART_CISM2%NOEVOLVE_SWAV) compset between 2000-2022 on Cheyenne. I have looked over the history fields table and haven't found that Soil Moisture or Evapotranspiration are included. I saw that the NCL library has a function to calculate ET <https://www.ncl.ucar.edu/Document/Functions/Crop/refevt_penman_fao56.shtml>, but it doesn't look like it would be easy to implement on a 22-year monthly time series. Are there any other options?

I also had an issue with the unit for GPP = gC/m^2/s or grams of Carbon per square meter per second. I wanted to update this to Kg of Carbon per square Km per day and have calculated it in R, but I do not know how to append these updated values to the netcdf file, it is only necessary for plotting because the values are so small that they do not appear in the legend when I plot the data in Panoply, I am open to other ideas!

Thank you!

 

[ah828]

I figured out you can calculate ET using Latent Heat Flux (EFLX_LH_TOT) and 2m Air Temperature (TSA) using the equation:

ET = LE/λ
​

Where ET = Evapotranspiration (kg m-2 s-1), and
LE = Latent heat flux (W m-2)
λ is the latent heat of vaporization (J kg-1) as calculated by:

λ = (2.501 − 0.00237 ∗ T air)10^6
​

Where Tair is Air temperature (deg C)

These formulae are implemented in the R Package "bigleaf" (Knauer et al. 2015)

​

Knauer J, El-Madany TS, Zaehle S, Migliavacca M (2018) Bigleaf—An R package for the calculation of physical and physiological ecosystem properties from eddy covariance data. PLoS ONE 13(8): e0201114. Bigleaf—An R package for the calculation of physical and physiological ecosystem properties from eddy covariance data

But where is the best place to implement these calculations (Matlab, R, Python, etc..) ?

 

[oleson]

H2OSOI (volumetric soil moisture; m3/m3) should be available in your history files. Also, SOILLIQ (liquid water content; kg/m2) and SOILICE (ice content; kg/m2). You should also be able to get total ET (mm/s) by summing QVEGE (canopy evaporation), QSOIL (ground/soil evaporation), and QVEGT (transpiration).

 

[ah828]

Thank you Keith. I located the H2OSOI variable, but wasn't initially sure if that was the best representation of soil moisture being limited to vegetated land units only. I also couldn't find any information indicating what depth that represents and if it includes root zone soil moisture (0-100cm), which is useful to know if I wanted to compare it to SMAP (Level 2/3: 0-5cm or Level 4: 0-100cm) Data Products. Do you happen to know, or could you point me in the right direction?

Thank you for the information on calculating ET, that method seems more straightforward!

 

[oleson]

H2OSOI is dimensioned by levsoi. There isn't a levsoi variable on the history file, but there is a levgrnd variable. levsoi and levgrnd are the same for the 20 levsoi layers. You can do ncdump -v levgrnd X.nc to get the layer node depths in meters:

levgrnd = 0.01, 0.04, 0.09, 0.16, 0.26, 0.4, 0.58, 0.8, 1.06, 1.36, 1.7,
2.08, 2.5, 2.99, 3.58, 4.27, 5.06, 5.95, 6.94, 8.03, 9.795, 13.32777,
19.48313, 28.87072, 41.99844 ;

So it includes root zone soil moisture.
There is a description of the soil layering in the CLM5 technical note:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

 

[Ali]

Hello,

I like to compute the root zone soil moisture (0-100cm) and I was wondering if I should consider the active soil layer when calculating the weighted average of soil moisture for each grid cell?

Here is what the CLM5 reference paper says:
"Note that since the number of active soil layers varies from grid cell to grid cell, users need to be careful when doing spatial averaging of soil moisture or carbon/nitrogen quantities since bedrock layers have very small prescribed constant soil moisture and carbon/nitrogen values."
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018MS001583

 

[slevis]

@Ali in our opinion the short answer is YES because there may exist grid cells with bedrock in the top meter of soil. Ultimately the decision is yours.

 

[Ali]

@slevis alright, thanks for your response.