GWETROOT units and

[dsanpo]

I downloaded agroclimatological data from the NASA POWER Data Viewer, specifically the variable Root Zone Soil Wetness (GWETROOT).
In the POWER parameter description, GWETROOT is defined as:
“The amount of water and water vapor available to plants in the root zone, generally considered to be the upper 200 cm of soil, expressed as the proportion of water present in a given amount of soil. Values range from 0 (dry) to 1 (saturated).”
However, in the official MERRA-2 documentation, GWETROOT is defined as:
“Relative soil moisture (fractional saturation) in the 0–100 cm root zone layer.”
So the depth definition differs (200 cm vs 100 cm). I’m trying to determine whether NASA POWER simply relabels the variable for agricultural users or whether the data have actually been rescaled or altered from the original MERRA-2 dataset.
Does anyone know if POWER applies any transformation to MERRA-2 GWETROOT, or if it simply reuses the raw 0–100 cm layer from MERRA-2? Any official reference or technical documentation link would be very helpful.

[mbosilov]

POWER does just mirror the MERRA-2 data, so the units and definition should be the same as MERRA-2. The depth of the root zone is 0-1m. Thank you for calling out this difference in the definitions, POWER is double checking their other parameters as well.

There is a MERRA-2 land constants file available, const_2d_lnd_Nx (M2CONXLND), which includes a variable, DZRZ, the thickness of the root zone, and happens to be 1.0m everywhere that there is a value of land fraction >0.0.

[dsanpo]

Thank you so much

[naluru]

POWER does not apply a transformation to the parameter, and this is indeed a mistake in the metadata. Thank you for bringing our attention to this detail. The updated definition should be reflected shortly.

[GES DISC - xpan2]

POWER does not apply a transformation to the parameter, and this is indeed a mistake in the metadata. Thank you for bringing our attention to this detail. The updated definition should be reflected shortly.

Please let us updated once this definition is corrected in your website. Thanks.