Thanks @skunwar, @FengLiu and @fliu for your updates.
For the issue of BELD3 vs. BELD4/BELD5, our current thinking is that future model releases may remove the option to use any version of BELD to obtain fractional land use information, instead requiring this information to be available through the MCIP files. No decision has been made, but since it seems possible to provide fractional land use information for any WRF LSM through MCIP (either because the wrfout files already contain this information for some LSM, or by using the MCIP IfGeo and InGeoFile option if this information isn’t in wrfout), there shouldn’t be a need for providing a separate fractional land use data set to the WBD module. Eliminating this option would eliminate the need to update this portion of the code as BELD evolves. In addition, BELD data is generally not available outside North America so requiring this information through MCIP would be the more generalized approach. The historic reason for obtaining this information from BELD3 likely was that it was not always possible to obtain fractional land use output from WRF. If you have any concerns about this potential change, please let us know.
For the compatibility issues between the current implementation of the CMAQ WBD scheme and the WRF NOAH LSM - in particular the issue of the first layer soil depth - you might be interested in a WRF sensitivity simulation performed by our former colleague @Patrick.C.Campbell who modified the NOAH LSM to use a 1 cm thick first layer instead of a 10 cm thick first layer and then used outputs from that modified version of WRF to drive the CMAQ with the WBD option turned on:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018MS001422
Our understanding is that most of the NOAH updates described in this paper - but importantly not the change of the first layer thickness that affects the CMAQ WBD calculations - have been implemented in the public version of WRF.
We should also note that the following statement in this paper “When running the unmodified off‐line WRF/Noah‐CMAQ, the soil moisture and temperature are adjusted in CMAQ from 10‐ to 1‐cm depth based on Darmenova et al. (2009), which creates additional uncertainty in model predictions” referred to an internal development version of CMAQ that was not publicly released. In the current public release version of CMAQ, no such adjustment is performed, and the WBD module expects layer 1 soil moisture to represent a depth of 1 cm.