Inquiry About BEP/BEM Urban Scheme Parameters in WRF Model

[xiaozi]

Dear community members,

I am a novice researcher using the BEP/BEM urban scheme in the WRF model (v4.5.1) to study the climate impacts of urban underlying surfaces. I have two key questions regarding parameter configuration and would sincerely appreciate your insights.

Background
My focus is on two critical parameters:

FRC_URB2D (urban fraction)
URB_PARAM
Core Questions

Parameter Relationship
Does FRC_URB2D influence how URB_PARAM is applied in practice? For example:
Is URB_PARAM scaled by FRC_URB2D (e.g., URB_PARAM × FRC_URB2D)?

Parameter Reading Logic
Based on my preliminary understanding of the code logic, the workflow might be:
The model first identifies urban grid cells via IVGTYP (vegetation type).
For urban grids, FRC_URB2D is read to determine the urban coverage.
URB_PARAM is then read as the urban parameter set.

Questions:
Is this workflow accurate?
Is the final parameter value calculated as URB_PARAM × FRC_URB2D?
Requests for Assistance

If official documentation or published studies clarify the mathematical relationship between these parameters, please share.
If you have practical experience (e.g., sensitivity tests) with these parameters, your insights would be invaluable.

 

[Ming Chen]

Please see my answers below:

Dear community members,

I am a novice researcher using the BEP/BEM urban scheme in the WRF model (v4.5.1) to study the climate impacts of urban underlying surfaces. I have two key questions regarding parameter configuration and would sincerely appreciate your insights.

Background
My focus is on two critical parameters:

FRC_URB2D (urban fraction)
URB_PARAM
Core Questions

Parameter Relationship
Does FRC_URB2D influence how URB_PARAM is applied in practice? For example:
Is URB_PARAM scaled by FRC_URB2D (e.g., URB_PARAM × FRC_URB2D)?

No, URB_PARAM doesn't change with FRC_URB2D.

Parameter Reading Logic
Based on my preliminary understanding of the code logic, the workflow might be:
The model first identifies urban grid cells via IVGTYP (vegetation type).
For urban grids, FRC_URB2D is read to determine the urban coverage.
URB_PARAM is then read as the urban parameter set.

Questions:
Is this workflow accurate?

WRF obtains information of IVGTYP, FRC_URB2D from initial input data. URB_PARAM is read if urban scheme is activated.

Is the final parameter value calculated as URB_PARAM × FRC_URB2D?
Requests for Assistance

No, URB_PARAM remains unchanged once they are read into WRF.

If official documentation or published studies clarify the mathematical relationship between these parameters, please share.
If you have practical experience (e.g., sensitivity tests) with these parameters, your insights would be invaluable.

Please refer to the papers below for better undersanding how urban modules work in WRF:
Chen, F., H. Kusaka, R. Bornstain, J. Ching, C.S.B. Grimmond, S. Grossman-Clarke, T. Loridan, K. Manning, A. Martilli, S. Miao, D. Sailor, F. Salamanca, H. Taha, M. Tewari, X. Wang, A. Wyszogrodzki, and C. Zhang, 2011: The integrated WRF/urban modeling system: development, evaluation, and applications to urban environmental problems. International Journal of Climatology, 31, 273-288. DOI: 10.1002/joc.2158.
doi:10.1002/joc.2158

Salamanca, F., and A. Martilli, 2010: A new building energy model coupled with an urban canopy parameterization for urban climate simulations––part II. Validation with one dimension off–line simulations. Theor. Appl. Climatol., 99, 345–356.
doi:10.1007/s00704-009-0143-8

Martilli A, Clappier A, and Rotach M.W., 2002: An urban surface exchange parameterization for mesoscale models. Bound.-Layer Meteorol., 104, 261–304.
doi:10.1023/A:1016099921195

 

[xiaozi]

Please see my answers below:

No, URB_PARAM doesn't change with FRC_URB2D.

WRF obtains information of IVGTYP, FRC_URB2D from initial input data. URB_PARAM is read if urban scheme is activated.

No, URB_PARAM remains unchanged once they are read into WRF.

Please refer to the papers below for better undersanding how urban modules work in WRF:
Chen, F., H. Kusaka, R. Bornstain, J. Ching, C.S.B. Grimmond, S. Grossman-Clarke, T. Loridan, K. Manning, A. Martilli, S. Miao, D. Sailor, F. Salamanca, H. Taha, M. Tewari, X. Wang, A. Wyszogrodzki, and C. Zhang, 2011: The integrated WRF/urban modeling system: development, evaluation, and applications to urban environmental problems. International Journal of Climatology, 31, 273-288. DOI: 10.1002/joc.2158.
doi:10.1002/joc.2158

Salamanca, F., and A. Martilli, 2010: A new building energy model coupled with an urban canopy parameterization for urban climate simulations––part II. Validation with one dimension off–line simulations. Theor. Appl. Climatol., 99, 345–356.
doi:10.1007/s00704-009-0143-8

Martilli A, Clappier A, and Rotach M.W., 2002: An urban surface exchange parameterization for mesoscale models. Bound.-Layer Meteorol., 104, 261–304.
doi:10.1023/A:1016099921195

Dear Professor Chen：

Thank you for your previous guidance on WRF applications. I’m currently integrating the CGCS_MODIS_LCZ_100m dataset as my base land surface input and have replaced the default FRC_URB2D variable with preprocessed custom urban fraction data. Two follow-up questions require your expertise:

Variable Priority Clarification
When activating the use_wudapt_lcz=1 parameter, does WRF:
Prioritize reading my substituted FRC_URB2D grid data?
Or still reference the urban type parameters defined in the URBPARM_LCZ.TBL?

Mixed Pixel Classification Logic
For grid cells where:
LU_INDEX indicates a non-urban category
But FRC_URB2D > 0
Would WRF:
Treat it as urban?
Consider it a mixed pixel with urban components despite the non-urban LU_INDEX?
Or strictly follow the LU_INDEX classification?

 

[Ming Chen]

Please see my answers below:

Dear Professor Chen：

Thank you for your previous guidance on WRF applications. I’m currently integrating the CGCS_MODIS_LCZ_100m dataset as my base land surface input and have replaced the default FRC_URB2D variable with preprocessed custom urban fraction data. Two follow-up questions require your expertise:

Variable Priority Clarification
When activating the use_wudapt_lcz=1 parameter, does WRF:
Prioritize reading my substituted FRC_URB2D grid data?
Or still reference the urban type parameters defined in the URBPARM_LCZ.TBL?

WRF will refer to urban parameters specified in URBPARM_LCZ.TBL.

Mixed Pixel Classification Logic
For grid cells where:
LU_INDEX indicates a non-urban category
But FRC_URB2D > 0
Would WRF:
Treat it as urban?
Consider it a mixed pixel with urban components despite the non-urban LU_INDEX?
Or strictly follow the LU_INDEX classification?

In this case WRF will treat the grid as a non-urban grid. All land parameters are specified based on IVGTYP at this grid.

Hope this is helpful for you. Please let me know if you have more questions.

 

[xiaozi]

Please see my answers below:


WRF will refer to urban parameters specified in URBPARM_LCZ.TBL.

In this case WRF will treat the grid as a non-urban grid. All land parameters are specified based on IVGTYP at this grid.

Hope this is helpful for you. Please let me know if you have more questions.

Thank you very much for your guidance, Professor Chen! Based on your response, I have new questions:
I want to use my self-generated FRC_URB2D and URB_PARAM variables instead of the table values defined in URBPARM_LCZ.TBL. In this case:
(1) Do I need to deactivate the CGCS_MODIS_LCZ_100m dataset?
(2) Should I set use_wudapt_lcz=0 to disable the LCZ scheme, ensuring the model directly reads my custom FRC_URB2D and URB_PARAM variables?