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Some questions about SMOIS and CANWAT


Hi WRF support,

I am running a real-case simulation using the Noah Land Surface Scheme. I have some questions about the inconsistencies between my met_em, wrfinput, and wrfout files regarding a few land-state variables.

The first one is CANWAT (canopy water). I was looking into my CANWAT field in my met_em and wrfinput files at my model initialization time, I found that the field is the same and non-zero between the two files, which is expected. However, when I looked into my wrfout file at the initial time, CANWAT is zero everywhere. Is this a normal model behavior? Does this mean that the CANWAT variable from the met_em or wrfinput files is not used directly in WRF integration? Based on what I read in module_initialize_real.F, I think it might be used to adjust soil moisture at the initial time, so perhaps soil moisture already accounts for the effects of pre-existing canopy water.

The second question is regarding SM (SMOIS) and ST (TSLB) variables in met_em and wrfinput files. I found that the layer order is flipped for these variables between the two files. I think someone asked about this a while ago (Soil T layers reversed in wrfinput from met_em files). I looked into the module_soil_pre.F code as Ming had suggested in that previous post and I think the layer order is flipped in the subroutines process_soil_real -> init_soil_2_real, which are called in module_initialize_real.F. Can someone please confirm this?

Thank you,


To answer your first question, you are right that CANWAT are non-zero and consistent between wrfinput and met_em. However, once WRF starts, CANWAT is reset to zero everywhere in phys/module_sf_noahdrv.F. Please see the following piece of code (lines 1970-1979):
! initialize canopy water to ZERO

! GO TO 110

! print*,'Note that canopy water content (CANWAT) is set to ZERO in LSMINIT'

DO J = jts,jtf

DO I = its,itf






For your 2nd question, yes your understanding of the model soil levels are correct.