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SMCREL negative over urban areas

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New member
Hi users,

I'm running WRFv4.2 with NOAH-LSM (incl. MODIS 21 class landcover and sfclay=1).
I did not switch on any urban canopy model.
I used ERA5 for initial and boundary conditions.

I'm trying to use WRF output Relative Soil Moisture (SMCREL).
However I view the variable and there are negative values over what would be described as urban areas within the landcover.
Soil moisture seems to be fine, however there is also some difference between urban vs non-urban.

I've tried to follow what I think is an older version of the relevant NOAH driver code (module_sf_noahdrv.F), and see that SMCREL was based on the fraction of excess moisture divided by the difference of soil wilting point and from soil saturation point (I assume these are set in SOILPARM.TBL). In the current code there's not much besides setting SMCREL to 1 for water bodies and ice.

Right now I'm not sure I can use my output.
Is it possible for me to estimate Relative Soil Moisture (SMCREL) from Soil Moisture (SMOIS)?


Associated SMOIS