Question about CM_AC_URB3D calculation

[Wang Zhikai]

Dear all WRF users,

I have a question regarding the WRF output variable CM_AC_URB3D, which is described as "CONSUMPTION OF THE AIR COND" in the Registry.EM_COMMON.

The unit for this variable is given as "W m⁻²". I would like to confirm how this area-averaged value is calculated. Specifically, does this value represent:

1. The air conditioning energy consumption averaged over the entire grid cell area?
2. Or, is it the energy consumption averaged only over the building footprint area within that grid cell?

Furthermore, it would be very grateful if someone could explain the calculation methodology for this value.

Best regards,
Zhikai

 

[Wang Zhikai]

Additionally, I would like to ask how to calculate the urban net all-wave radiation, sensible heat flux, latent heat flux, and ground heat flux in WRF BEM to reproduce the results from this paper's figure (The effectiveness of cool and green roofs in mitigating urban heat island and improving human thermal comfort Redirecting )

The paper mentions that these values are averaged over urban grid cells and for a specific time period. The caption for the figure is as follows:


Fig. 7. Impact of green and cool roofs on urban surface energy balance components: (a) net all-wave radiation (Rn), (b) sensible heat flux (SH), (c) latent heat flux (LH), and (d) ground heat flux (G). Upward flux is defined as positive. Each curve represents the difference between the corresponding scenario and the reference scenario. All values are averaged over urban grid cells in Berlin and averaged over 18–19 July 2014.


I am unsure whether I should enable the following 2D variables in the Registry:
SH_URB2D "SH_URB" "SENSIBLE HEAT FLUX FROM URBAN SFC"
LH_URB2D "LH_URB" "LATENT HEAT FLUX FROM URBAN SFC"
G_URB2D "G_URB" "GROUND HEAT FLUX INTO URBAN"
RN_URB2D "RN_URB" "NET RADIATION ON URBAN SFC"


Or if the calculation is related to the following 3D variables, which seem to represent fluxes from different urban surface facets (wall, roof, ground):
"SFW1_URB3D" "SENSIBLE HEAT FLUX FROM URBAN SFC" "W m{-2}"
"SFW2_URB3D" "SENSIBLE HEAT FLUX FROM URBAN SFC" "W m{-2}"
"SFR_URB3D" "SENSIBLE HEAT FLUX FROM URBAN SFC" "W m{-2}"
"SFG_URB3D" "SENSIBLE HEAT FLUX FROM URBAN SFC" "W m{-2}"

"LFR_URB3D" "LATENT HEAT FLUX FROM URBAN SFC" "W m{-2}"
"LFG_URB3D" "LATENT HEAT FLUX FROM URBAN SFC" "W m{-2}"


I apologize for the inconvenience. Could Dr.Chen @Ming Chen or anyone else please help us with this question, or direct us to the resources for checking this information?

Thank you very much for your time and consideration.

 

[Ming Chen]

I will check with our expert and hopefully he has a quick answer. At the same time, please see whether you can find some helpful information in the papers below:

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

 

[Wang Zhikai]

I will check with our expert and hopefully he has a quick answer. At the same time, please see whether you can find some helpful information in the papers below:

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

Thank you for your reply, and thank you for providing these valuable references. I'll dive into them now and see what I can find.

 

[cenlinhe]

The CM_AC_URB3D should be the value for the urban portion of a grid cell.
The 2D variables *_URB2D should be used for total energy balance calculation (these variables are only for urban portion of each grid cell). If you want to know more detailed energy balance for each urban building vertical layer, you can use the 3D variables for diagnosis. I am not sure which variables the paper authors used. You may want to email the paper authors directly to ask how they produced that figure.

 

[Wang Zhikai]

The CM_AC_URB3D should be the value for the urban portion of a grid cell.
CM_AC_URB3D 应该是网格单元城市部分的值。
The 2D variables *_URB2D should be used for total energy balance calculation (these variables are only for urban portion of each grid cell). If you want to know more detailed energy balance for each urban building vertical layer, you can use the 3D variables for diagnosis. I am not sure which variables the paper authors used. You may want to email the paper authors directly to ask how they produced that figure.
二维变量 *_URB2D 应该用于计算总能量平衡（这些变量仅适用于每个网格单元的城市部分）。如果您想了解每个城市建筑垂直层的更详细的能量平衡，可以使用三维变量进行诊断。我不确定论文作者使用了哪些变量。您可以直接给论文作者发送电子邮件，询问他们是如何生成该图的。

Thank you for your reply! I still have some follow-up questions:

1. I recently calculated the urban fraction of HFX and LH manually. I was wondering if there is any difference between the HFX and LH values in the WRFOUT files and the SH_URB2D and LH_URB2D variables?

2. Additionally, according to the surface energy balance equation, can we consider RN_URB to be approximately equivalent to Qnet, SH_URB to QH, LH_URB to QLE, and G_URB to Qstor?

3. I would also like to report a potential issue. In my BEM simulations with WRF v4.3.3, the TR_URB (urban roof skin temperature) variable does not change, which means it is not being output correctly. I am simply curious if this problem has been resolved in a later version.

Finally, thank you very much for your response and for your team's valuable contributions.


This equation comes from 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

where the term Q net is the net all wave radiation, Q H the sensible heat flux, Q LE the latent heat flux, and finally Q stor the net heat stored in the urban area. It is important to mention that in an urban area the heat fluxes (Q H and Q LE) are not only the result of the partitioning of the net radiation, as it happens for natural surfaces, but they have a component due to human activities (anthropogenic heat).