the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 May 2024
Coupling the urban canopy model TEB (SURFEXv9.0) with the radiation model SPARTACUS-Urbanv0.6.1 for more realistic urban radiative exchange calculation
Abstract. The urban canopy model TEB is coupled with the radiation model SPARTACUS-Urban to improve both the urban geometry simplification and radiative transfer calculation. SPARTACUS-Urban assumes that the probability density function of wall-to-wall and ground-to-wall distances follows a decreasing exponential. This matches better the distributions in real cities compared to the infinitely-long street canyon employed by the classical TEB. SPARTACUS-Urban solves the radiative transfer equation using the discrete ordinate method. This allows to take into account physical processes like the interaction of radiation with air in the urban canopy layer, spectral dependency of urban material reflectivities, or specular reflections. Such processes would be more difficult to account for with the radiosity method used by the classical TEB. With SPARTACUS-Urban, the mean radiant temperature, a crucial parameter for outdoor human thermal comfort, can be calculated using the radiative fluxes in vertical and horizontal direction incident on a human body in the urban environment. TEB-SPARTACUS is validated by comparing the solar and terrestrial urban radiation budget observables with those simulated by the Monte-Carlo-based HTRDR-Urban reference model for procedurally-generated urban districts mimicking the Local Climate Zones. An improvement is found for almost all radiative observables and urban morphologies for direct solar, diffuse solar, and terrestrial infrared radiation. TEB-SPARTACUS might therefore lead to more realistic results for building energy consumption, outdoor human thermal comfort, or the urban heat island effect.
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RC1: 'Comment on egusphere-2024-1118', Anonymous Referee #1, 30 Aug 2024
General Comments
The paper outlines a new development to the building/urban representation within the Town Energy Balance model. This new approach replaces the currently used street-canyon assumption with the urban geometry assumptions behind the SPARTACUS-Surface model that suggest that the separation between buildings can be described using an exponential distribution. The new model iteration does not utilize many other capabilities of SPARTACUS, and instead retains the assumption from the street-canyon that buildings and trees are all of one height (although does implement the multiple layers of SPARTACUS). This omission impacts some of the results shown within this paper, such as a lack of roof shadowing, which would be addressed if the full form of SPARTACUS-Surface was utilized. Despite this, the work here is a useful development, and shows movement towards more realistic urban representation than the current street canyon approach.
Specific Comments
- The three model setups (TEB, TEB-SPARTACUS, and HTRDR-Urban) use different urban form/tree inputs which if changed would alter the motivation and results within the paper. It is clear that the two TEB simulations differ only through their building separation (street canyon vs. exponential separation) assumptions and tree representation (a turbid block vs. a SPARTACUS tree), however within the HTRDR-Urban simulations the building height and tree representation are different from either TEB model. A further point is that the HTRDR-Urban simulations sometimes include pitched roofs – a feature that SPARTACUS-Urban could represent. It may be fairer to conduct simulations that are more similar, as when you compare two scenes that are different, both models will give different answers. The statement at L370 – ‘SPARTACUS-Urban is perfectly suited for dealing with such a variety of building height; the TEB geometrical input parameters would have to be modified’ does reflect this, but the authors should consider mentioning this earlier in the paper, perhaps with a test to show what differences would have arisen if the full SPARTACUS version was used.
- The calculation of mean radiant temperature (MRT) for the new model configuration is discussed, however no results are given within this paper. It would be interesting to see the MRT values that are obtained from the new model, as well as a comparison – either to observations or to other modelled MRT, if this is dedicated a whole section within the paper. The calculations of MRT in TEB-SPARTACUS (L155-160) themselves need more explanation, and some decisions made are not well justified. For example, the authors state (L175) that the radiative fluxes for the MRT calculation are determined at ground level, rather than at 1 m. What are the differences between the MRT if this is not neglected? As the TEB-SPARTACUS fluxes are computed at regular intervals (default 1 m) then would be an easy change to make? Finally, in L162 it is unclear why the values of the body albedo and emissivity are chosen.
- What is the reasoning behind choosing the morphologies tested and LCZ parameters? Some LCZs have large variations in urban form across them, so what is the rationale in choosing the combinations that are tested here? Further, could you have used real-world geometries rather than the scenes that have been created? Some LCZ types that have been created for the previous work but are no standard LCZ classifications, e.g., a-b or af, could be explained in the text. Please introduce some more discussion on the scenes themselves – the tree properties are given in the text but not any urban form properties – and then use these to aid discussion within the results sections (e.g., for Figure 3).
- The authors state that the TEB levels are different to the SPARTACUS levels. Could this be modified to keep consistency rather than interpolating between the two and introducing error?
- In the terrestrial radiation section there is little explanation of the surface temperature representation in each model, and whether they incorporate both sunlit and shaded surface temperature. How are these prescribed? Additionally, there is no explanation of why the chosen temperature is used. Please expand on the assumptions made in these calculations.
Technical Comments
- There are some grammatical issues throughout the paper, such as misspellings of ‘leave’ and ‘plane area fraction’. Please go through the paper and check for grammatical errors.
- I am unsure how useful Tables 1 and 2 are, given that they mostly contain information that can be found in the SPARTACUS-Surface user manual. Also, most columns are stated ‘Set to 0’ which is user-specified. Please consider altering these to make them more useful to the reader.
- Why were optical properties of buildings (0.3, L237) and trees chosen? It is also unclear why the albedo of buildings changed in the simulations with trees (L240).
- The results in the sections of direct-only and diffuse-only radiation are very similar and could be combined or mentioned and added to the supplementary material. Each discussion of the results in this section is very short.
- Much of the paper is structured into bullet points, which makes the paper more challenging to read. Particularly this is the case in the discussion section of the paper, which reads more like a conclusions section. I would advise altering this in some sections of the paper.
- Quantitative error values would be useful in the results, discussions, and conclusions sections, rather than just describing decreases and increases in error. Where numerical values are given in the conclusions, e.g., L355 – ‘a factor of 5 less uncertainty’ it is unclear, and the full results for all the morphologies are not included.
- The conclusions section outlines a restriction of ‘only urban districts with one building type and morphology have been investigated’ – this is untrue as the scenes you use are heterogenous (buildings are not identical with one prescribed height. This is also mentioned in line 410 in the conclusions. Please rephrase this.
- Some of the variable symbols used are non-standard, so in the results section it would be good to have a reminder of these for the reader.
- In some of the figures (e.g. Figure 2) it is hard to tell the difference between some of the lines. Please consider altering the line colours and styles so that all results are easily seen.
- In L292 you use QT/QD where in other places this would be just QT (e.g. L295). Please modify this and check for any other occasions in the text.
- For the readers, it would be useful to add the plots for the solar zenith angles tested into the supplementary material for the other morphology types.
Citation: https://doi.org/10.5194/egusphere-2024-1118-RC1 -
RC2: 'Comment on egusphere-2024-1118', Anonymous Referee #2, 01 Sep 2024
This study coupled the urban canopy model TEB with the radiation model SPARTACUS-Urban to improve both the urban geometry simplification and radiative transfer calculation. With SPARTACUS-Urban, the mean radiant temperature is calculated in a more realistic way by using the radiative fluxes in vertical and horizontal direction incident on a human body. TEB-SPARTACUS was validated by comparing the solar and terrestrial urban radiation budget observables with those simulated by the Monte-Carlo-based HTRDR-Urban reference model, which showed improved model performance for almost all radiative observables and urban morphologies for direct solar, diffuse solar, and terrestrial infrared radiation. Overall, this study represents an important model development effort to improve urban radiative processes and can potentially contribute to future urban climate studies. The manuscript overall reads fine but there are a few key places that lack clear descriptions and sufficient details. I would suggest the authors address those issues before this study can be considered for potential publications. Please see my specific comments/suggestions below.
Specific comments:
- Section 2.1: The authors did not change the geometrical complexity and input parameters of TEB in this study. Have the authors tested how sensitive the urban simulation results are to these parameters? This would be a good model uncertainty quantification exercise.
- Section 2.2 and Figure 1: Should the parameter be “delta_spts,max” (used in Figure 1) or “delta_sps,max” (used in the text). Please double check to make sure this is consistent. Also, the text description of the setup of “delta_spts,max” (or “delta_sps,max”) is not very clear to me based on Figrue 1 demonstration. In the text, it says that “delta_sps,max” is set up to the height from the ground to tree height, which is not the case demonstrated in Figure 1a.
- Equation (6): Should it be “Tagg^4 = ….”?
- Lines 125-130: (1) Does SPARTACUS-Urban solve surface energy balance for each type of urban surface covers (such as the Figure 1 example) and then aggregate the fluxes together, or directly use the aggregated surface properties (e.g., albedo, emissivity, etc.) to solve the energy balance for the “effective” aggregated surface as a whole? This needs to be clarified. (2) It may be very useful if there is a simple diagram to demonstrate the surface energy balance and key processes considered for different surface types (e.g., building, tree, air).
- Section 2.3: (1) There needs to be a description of data sources or references that indicate how the current TEB input parameters and the SPARTACUS-Urban parameters came from (e.g., those in Table 1). (2) Also, based on the description here, currently the model does not account for radiative interactions between trees and buildings (e.g., multi-reflection between trees and walls), right? This needs to be clarified in the text. (3) There is also a need to clarify how the SPARTACUS-Urban output parameters (Table 2) are coupled with other TEB energy calculations. This is related to my #4 question above in terms of how the surface energy balance and budget are solved in this coupled SPARTACUS-Urban-TEB system. Does SPARTACUS-Urban just return the aggregated “effective” radiative flux and parameters to TEB for the entire surface energy balance calculation or does it solve for the energy balance in each surface type/facet individually?
- Equations 12 and 14: Where do those coefficients (e.g., 0.88, 0.06, 0.06, 0.308, 14.774) come from? Please also provide the references for these equations.
- Equation 17: I would suggest providing the value of Nr used for different solar elevation angles in this study.
- Section 3.4: I would suggest explicitly stating that for each test, the HTRDR-Urban, TEB-Classical, and TEB-SPARTACUS used exactly the same urban geometries configuration (is my understanding correctly?). If the configurations are different in three models, then this would not be an apple-to-apple evaluation/comparison. Please clarify.
- Figure 2 caption: Please also include a description of Q_D.
- Section 4.1.2: Are the mutual SW impacts of tree shading on building and building shading on tree considered in TEB-SPARTACUS (I assume they are included in HTRDR-Urban?)? If this is the case, then it may contribute to the discrepancies between TEB-SPARTACUS (or TEB-Classic) and HTRDR-Urban. This needs to be clarified. Similarly, some clarifications are needed for Section 4.3.2 in terms of the LW radiative interaction between trees and buildings.
- Following my #1 comment above, it would be useful if there is an uncertainty section that quantifies the sensitivity of TEB-SPARTACUS simulations results to several key TEB-SPARTACUS input parameters (e.g., albedo, emissivity). This can be just idealized TEB-SPARTACUS simulations without the need to comparing with HTRDR-Urban, which can give users an idea of what the relative importance of those uncertain input parameters and shed lights on future model and/or input data improvement.
Citation: https://doi.org/10.5194/egusphere-2024-1118-RC2 -
AC1: 'Response to both reviewers comments', Robert Schoetter, 31 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1118/egusphere-2024-1118-AC1-supplement.pdf
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