Urban Densification and Outdoor Thermal Comfort: Scenario-Based Analysis in Zurich’s Altstetten–Albisrieden District

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study entitled "Balancing Growth and Liveability: Evaluating Densification Means Through Scenario-Based Analysis in Zurich's Altstet-ten-Albisrieden District" investigated redevelopment approaches for urban densification and transformation in the Altstetten-Albisrieden district. However, major revisions are required before potential publication.

 

Major Comments:

• The title is suggested to be revised to "Balancing Urbanization and Livability…"
• I suggest a background on BZO2016 in the Introduction and summarizing the research questions (raised in Section 2.1, Lines 150-156) in the last paragraph of the Introduction.
• The methodological framework (Figure 2) presents only the paper's structure; please illustrate the research methodology with a graphical diagram.
• The presentation of the methodology could be appropriately abbreviated, and certain optional content could be transferred to the appendix.
• It is recommended to include an in-depth analysis of the contribution of this investigation to enhancing the urban thermal comfort in the discussion section, as well as related policy implications.

 

Specific Comments:

1. The labels in Figures 3 and 5 are too small to read. Please check the similar issues in the main text.
2. I propose to present the collected data and their information in a table.
3. Lines 457-462: I suggest summarizing the input and output variables of the SOLWEIG simulation and their meanings in a table.
4. Have the simulations from SOLWEIG been validated?
5. Lines 477-478: Why are vegetation and other urban features excluded? These are essential for urban heat exchange.
6. Figure 4 contains too few data points for fitting and is recommended for removal.
7. Lines 874-887 could be transferred to the Discussion.

Author Response

Comment 1: The title is suggested to be revised to "Balancing Urbanisation and Livability…"

Reply: Many thanks for the suggestion. I have revised the title of the paper accordingly.

 

Comment 2: I suggest a background on BZO2016 in the Introduction and summarising the research questions (raised in Section 2.1, Lines 150-156) in the last paragraph of the Introduction.

Reply: Many thanks for the suggestion. I agree with you on this, and it appears more logical. I have moved the paragraph of BZO2016 from Section 3.1 to the Introduction, and added a short summary of the research questions in the Introduction.

 

Comment 3: The methodological framework (Figure 2) presents only the paper's structure; please illustrate the research methodology with a graphical diagram.

Reply: Thank you very much for this suggestion. I have revised the figure.

 

Comment 4: The presentation of the methodology could be appropriately abbreviated, and certain optional content could be transferred to the appendix.

Reply: Thank you very much for this suggestion. I have moved some detailed information to Appendix A.

 

Comment 5: It is recommended to include an in-depth analysis of the contribution of this investigation to enhancing the urban thermal comfort in the discussion section, as well as related policy implications.

Reply: Thank you very much for this suggestion. I have added some recommendations for future development in the Conclusion.

 

Comment 6: The labels in Figures 3 and 5 are too small to read. Please check the similar issues in the main text.

Reply: Thanks for the comments, I have revised all the figures.

 

Comment 7: I propose to present the collected data and their information in a table.

Reply: Thanks for the comments, I have added this table as Appendix A.1.

 

Comment 8: Lines 457-462: I suggest summarising the input and output variables of the SOLWEIG simulation and their meanings in a table.

Reply: Thanks for the comment. I have added a table of SOLWEIG input data in the Appendix.

 

Comment 9: Have the simulations from SOLWEIG been validated?

Reply: Thank you very much for raising this important point regarding validation. Since this study focused on scenario-based analysis through hypothetical building geometries and estimated scenarios, direct validation against field measurements was not feasible. However, we noted that the UMEP application, as a plug-in of QGIS, and its SOLWEIG model for simulating mean radiant temperature (Tmrt) have been extensively validated in previous studies for various urban environments. For example, Lindberg et al. (2008) showed excellent agreement with measured MRT (R² = 0.94, RMSE ≈ 4.8 K) in real-world courtyards, and further studies have confirmed performance across varied urban forms and vegetation conditions. A benchmark comparison by Gál & Kántor (2020) found that SOLWEIG performs comparably to other established microclimate models, such as ENVI-Met and RayMan Pro. We have added the above explanation and these citations to the Methods section to clarify the credibility of our simulation approach, despite the lack of direct measurement for our specific scenarios.

 

Comment 10: Lines 477-478: Why are vegetation and other urban features excluded? These are essential for urban heat exchange.

Reply: Thanks for the comment. I have revised Section 2.6.3 in the Methods to clarify the reason of excluding vegetation in the scenario simulations.

 

Comment 11: Figure 4 contains too few data points for fitting and is recommended for removal.

Reply: Many thanks for this suggestion. I have moved this figure to the Appendix.

 

Comment 12: Lines 874-887 could be transferred to the Discussion.

Reply: Thank you very much for this suggestion. I have moved this paragraph to a new section (Section 4.4) in the Discussion.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript, the authors focused on the Altstetten-Albisrieden district of Zurich based on geographic, building, and meteorological information data, and explored the impact of urban densification development on urban form and outdoor thermal comfort through a scenario analysis, which helped to quantify the relationship between urban densification development and the microclimate, and provided an empirical basis for climate-resilient urban planning. Based on novelty and urban planning implications, I believe that this work may be suitable for publication in a land journal after the following issues are properly addressed.

The detailed comments are as follows:

1. Some of the conclusions in the abstract need to be quantified. The abstract mentions that “appropriate measures for densification can significantly contribute to the development of livable cities,” but the quantitative effects of specific scenarios are not specified, and it is recommended that key data be added.
2. The abstract consisted of five main elements: background and current status of the study, methodology, data, results, and significance, while the tools used in the paper were not the main ones. For example, QGIS, UMEP, R. It is recommended that the abstract be reworked.
3. The introduction lacked the current state of research on balanced growth and livability, and urban densification.
4. There was no explanation for the exclusion of urban vegetation in the UMEP simulations, nor was there any discussion of the effect of the exclusion of urban vegetation on the results.
5. The title referred to “balanced growth and livability,” but the paper did not show any analysis of the correlation between urban densification and balanced growth and livability.
6. Lack of advantages and limitations in the discussion.
7. There was a lack of data to support the conclusions.
8. Please carefully check the references. Such as, the 23rd reference lacks an article page number.
9. Please revise the text in Figures 2, 5, 12, and 13 to the appropriate size, as it's not very clear currently.

Author Response

Comment 1: Some of the conclusions in the abstract need to be quantified. The abstract mentions that “appropriate measures for densification can significantly contribute to the development of livable cities,” but the quantitative effects of specific scenarios are not specified, and it is recommended that key data be added.

Reply: Many thanks for this suggestion. I have revised the abstract.

 

Comment 2: The abstract consisted of five main elements: background and current status of the study, methodology, data, results, and significance, while the tools used in the paper were not the main ones. For example, QGIS, UMEP, R. It is recommended that the abstract be reworked.

Reply: Many thanks for this suggestion. I have revised the abstract.

 

Comment 3: The introduction lacked the current state of research on balanced growth and livability, and urban densification.

Reply: Many thanks for this suggestion. I have added some relevant literature review in the Introduction.

 

Comment 4: There was no explanation for the exclusion of urban vegetation in the UMEP simulations, nor was there any discussion of the effect of the exclusion of urban vegetation on the results.

Reply: Thanks for the comment. I have revised Section 2.6.3 in the Methods to clarify the reason for excluding vegetation in the scenario simulations.

 

Comment 5: The title referred to “balanced growth and livability,” but the paper did not show any analysis of the correlation between urban densification and balanced growth and livability.

Reply: Thank you for this valuable comment. I agree that the original title could be interpreted as suggesting a direct analysis of balanced growth and livability, which is beyond the primary scope of this study. To clarify, we have revised the title to: “Urban Densification and Outdoor Thermal Comfort: Scenario-Based Analysis in Zurich’s Altstetten-Albisrieden District.” This revised title better reflects our focus on the microclimatic implications of densification strategies.”

 

Comment 6: Lack of advantages and limitations in the discussion.

Reply: Thanks for the comment. I have added Section 4.4 to the Discussion to address the study's limitations.

 

Comment 7: There was a lack of data to support the conclusions.

Reply: Thanks for the comment. I revised the Conclusion.

 

Comment 8: Please carefully check the references. Such as, the 23rd reference lacks an article page number.

Reply: Many thanks for this suggestion. I have added the page number of the paper and checked other references to avoid such mistakes.

 

Comment 9: Please revise the text in Figures 2, 5, 12, and 13 to the appropriate size, as it's not very clear currently.

Reply: Many thanks for this suggestion. I have revised all the figures.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Manuscript: “Balancing Growth and Liveability: Evaluating Densification Means Through Scenario-Based Analysis in Zurich’s Altstetten-Albisrieden District” addresses a highly relevant and timely urban planning topic — the challenge of balancing increased building density with maintaining quality of life in urban districts. The authors focus on analyzing five densification scenarios in the Altstetten-Albisrieden district of Zurich, using simulation tools to assess the impact of urban transformation on outdoor thermal comfort at the neighborhood scale. The study has significant scientific and practical potential, and its results may be useful for both researchers and urban planning practitioners.

Despite its many strengths, the article requires several important clarifications and additions, which would help to further improve its clarity and scientific rigor:
Suggestions for Improvement:
1. Consistency of the article’s aim between the abstract and the introduction - The aim of the study should be stated consistently in both the abstract and the introduction. Currently, there are discrepancies — the introduction emphasizes the need to answer research questions concerning urban form and thermal comfort, while the abstract focuses more on the general challenges of densification and the tools used in the analysis.
2. Scope of the abstract - The abstract should not only describe the general context and tools but also: clearly indicate the research method used; specify what kind of data was analyzed; summarize the main findings and conclusions drawn from the study.
3. Methodology section
Although the methodology section is extensive and detailed, it lacks a clear mapping between the described methods and the research questions (Questions 1–4). It would be helpful to explicitly indicate which methods correspond to which specific research questions.
Description of the analyses used and their significance for the study
The article states that certain analyses generated datasets for simulation, but it does not specify: what kinds of analyses were conducted (e.g., spatial, statistical?); what exact data was produced and on what assumptions it was based; how these results were transformed into inputs for the simulations (e.g., for the UMEP model).
For the study to be replicable, it is essential to describe this data processing path in more detail.
4. The process leading from the analysis of the existing state, through the identification of densification potential, to the development and simulation of scenarios should be described step by step in a clear and traceable way. Currently, the reader is left to infer some steps and relationships in the research process. A precise description will enable other researchers to repeat or adapt this methodology.
5. Reducing sentence complexity. Many sentences include too much information at once. For example: “Consequently, all buildings have been classified into three distinct categories...” – This sentence is grammatically correct, but it could be shortened or split into two for better readability.
At times, the text includes unnecessary repetition. For instance: “This scenario evaluated the moderate redevelopment of parcels containing buildings constructed after 1925.” – Since “redevelopment” implies prior development, the phrase could be simplified to “parcels developed after 1925.”
Certain phrases are structurally correct but difficult to follow. For example: “Given that the majority of the involved densified parcels were assumed to conform to the BZO2016 for regulated development intensity...” – This could be rephrased more clearly to enhance readability.

Conclusion:
The article constitutes a valuable contribution to the debate on sustainable urban transformation. I recommend its publication after the authors introduce the above-mentioned improvements, which will enhance the internal coherence of the manuscript as well as the clarity and transparency of the applied research methodology.

Author Response

Comment 1: Consistency of the article’s aim between the abstract and the introduction - The aim of the study should be stated consistently in both the abstract and the introduction. Currently, there are discrepancies — the introduction emphasises the need to answer research questions concerning urban form and thermal comfort, while the abstract focuses more on the general challenges of densification and the tools used in the analysis.

Reply: Many thanks for this suggestion. I have revised the abstract to ensure consistency with the paper's contents.

 

Comment 2: Scope of the abstract - The abstract should not only describe the general context and tools but also: clearly indicate the research method used; specify what kind of data was analyzed; summarize the main findings and conclusions drawn from the study.

Reply: Many thanks for this suggestion. I have revised the abstract as per your suggestion.

 

Comment 3: Methodology section:

• Although the methodology section is extensive and detailed, it lacks a clear mapping between the described methods and the research questions (Questions 1–4). It would be helpful to explicitly indicate which methods correspond to which specific research questions.
• Description of the analyses used and their significance for the study
• The article states that certain analyses generated datasets for simulation, but it does not specify: what kinds of analyses were conducted (e.g., spatial, statistical?); what exact data was produced and on what assumptions it was based; how these results were transformed into inputs for the simulations (e.g., for the UMEP model). For the study to be replicable, it is essential to describe this data processing path in more detail.

Reply: Many thanks for these comments.

• I have redeveloped the framework to map the overall methods and added another figure to illustrate the structure of the whole paper. Both indicate the specific methods and steps corresponding to the particular research questions and results.
• I have revised Section 2.1 to clarify the significance of the analysis for the study.
• I have revised most texts in the Methods to add more details to describe the workflow. In addition, I have added a table in the Appendix to summarise the input variables when applying the SOLWEIG model for microclimate simulation.

 

Comment 4: The process leading from the analysis of the existing state, through the identification of densification potential, to the development and simulation of scenarios should be described step by step in a clear and traceable way. Currently, the reader is left to infer some steps and relationships in the research process. A precise description will enable other researchers to repeat or adapt this methodology.

Reply: Thank you very much for the comments. I have added some content to most sections in the Methods to explain the workflows step by step.

 

Comment 5: Reducing sentence complexity. Many sentences include too much information at once. For example: “Consequently, all buildings have been classified into three distinct categories...” – This sentence is grammatically correct, but it could be shortened or split into two for better readability.

 At times, the text includes unnecessary repetition. For instance: “This scenario evaluated the moderate redevelopment of parcels containing buildings constructed after 1925.” – Since “redevelopment” implies prior development, the phrase could be simplified to “parcels developed after 1925.”

 Certain phrases are structurally correct but difficult to follow. For example: “Given that the majority of the involved densified parcels were assumed to conform to the BZO2016 for regulated development intensity...” – This could be rephrased more clearly to enhance readability.

Reply: Many thanks for this suggestion. I have revised the text to improve readability..

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been considerably improved, and I would suggest a minor revision.

1. I recommend removing Figure 4 or transferring it to the Appendix.
2. P28: “Nevertheless, this study has some limitations.” Combined with the following paragraph.

Author Response

Comment 1: I recommend removing Figure 4 or transferring it to the Appendix.

Reply: Many thanks for the suggestion. I have removed Figure 4. 

Comment 2: P28: “Nevertheless, this study has some limitations.” Combined with the following paragraph.

Reply: Thanks for pointing out this mistake. I have corrected it.