Compute minimum soil water potential Soil PSI min

[kunstler]

Benito Garzon et al. 2017 GEB computed Soil PSI min from

• ERA-INTERIM volumetric soil water content (spatial resolution (10 x 15 km)
  https://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/

• Soil water texture data from JRC Europe
  http://eusoils.jrc.ec.europa.eu/wrb/

https://esdac.jrc.ec.europa.eu/content/european-soil-database-v2-raster-library-1kmx1km
https://esdac.jrc.ec.europa.eu/content/sgdbe-attributes#TEXT_SRF_DOM dominant surface

The for each plot the max volumetric soil water content Wmax was computed as mean of monthly data for 5 wetter year and minimum for 5 driest year Wmin. For each soil category computed water potential at maximum hydratation PSImax

Then PSImin is computed PSImin = PSImax * (Wmin/Wmax)^b with b computed per soil type.

[kunstler]

In TeraClimate their soil water content per month at 4x4km

https://www.nature.com/articles/sdata2017191.pdf

They use a one-dimensional Water budget model modified from https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1111%2Fgcb.12026&file=gcb12026-sup-0001-AppendixA.doc

But they don't provide soil water capacity on soil water content in mm.

Thy used extractable soil water capacity data at 0.5° from https://hess.copernicus.org/articles/20/1459/2016/hess-20-1459-2016.pdf In this data the Root zone storage capacity is inversely estimated from remote sensing data of evapotranspiration from MODIS and Precipitation data. see sr_cru_2yrs.asc

Should we recompute this by interpolation as they did ? or simply compute the maximum of the time series?

Then this need to be converted in soil volumetric content

[kunstler]

soil grid provide clay and sand percentage at global scale at 250 x 250m scale.

https://www.isric.org/explore/soilgrids this can be used to compute

[kunstler]

But in Marta paper how soil depth is affecting the soil water potential ?

[kunstler]

An alternative to Campbell equation to compute soil potential (as used in Benito Garzon et al. 2017 GEB ) is the van Genuchten model (as used in SurEau)

See Tuller, M., & Or, D. (2005). WATER RETENTION AND CHARACTERISTIC CURVE. In Encyclopedia of Soils in the Environment (pp. 278–289). Elsevier. https://doi.org/10.1016/B0-12-348530-4/00376-3
for a review of models

[kunstler]

TerraClimate provide water content in mm but pedotransfer function use SWC in % of volume. The ERA Interim Marta used is in % of volume. So if use percentage of soil water content max (mm/mm) this doesn’t work.