Relevance of Ground and Wall Albedo for Outdoor Thermal Comfort in Tropical Savanna Climates: Evidence from Parametric Simulations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This work investigates the impact of ground and wall albedo on outdoor thermal comfort (OTC) in tropical savanna climates using parametric simulations in ENVI-met. By testing albedo ranges (ground: 0.2–0.8; walls: 0.05–0.90) with fixed emissivity, the authors found that wall albedo significantly reduces the Universal Thermal Climate Index (UTCI) by up to 2.80°C, while ground albedo had minimal effect (mean UTCI change 0.44°C). High ground albedo was shown to offset wall albedo’s cooling benefits, particularly in shaded areas, due to reflected radiation interactions. Material properties like transparency (e.g., glass) also influenced outcomes, highlighting the need to consider factors beyond albedo. Overall, I find this work interesting, especially the conclusion is fascinating. I only have minor comments:

1. ​​Material Practicality​​: While the parametric simulations explore a wide range of albedo values (e.g., wall albedo up to 0.9), the practicality of implementing such highly reflective materials (e.g., aluminum with 0.9 albedo) in tropical urban contexts could be briefly addressed. For instance, durability, maintenance (e.g., soiling effects), or glare concerns might limit real-world applicability, and a short discussion would contextualize the findings.

2. ​​Emissivity Assumption​​: The study fixes emissivity at 0.9 for all materials to isolate albedo effects. However, emissivity varies across real-world materials (e.g., glass vs. concrete). A brief sensitivity analysis or acknowledgment of how emissivity variability might influence UTCI could enhance the technical rigor.

3. ​​Non-Linear Wall Albedo Effects​​: The non-linear relationship between wall albedo and UTCI (peaking at intermediate albedo values) is intriguing but not fully explored. A deeper technical discussion on the radiative balance (e.g., interplay of shortwave reflection, longwave emission, and material transparency like glass) or thermal mass differences (e.g., aluminum vs. concrete) might clarify the underlying physics driving this pattern.

Author Response

Response to Reviewer 1

Comment 1: While the parametric simulations explore a wide range of albedo values (e.g., wall albedo up to 0.9), the practicality of implementing such highly reflective materials (e.g., aluminum with 0.9 albedo) in tropical urban contexts could be briefly addressed. For instance, durability, maintenance (e.g., soiling effects), or glare concerns might limit real-world applicability, and a short discussion would contextualize the findings.
Response: We thank the reviewer for highlighting the need to address material practicality. We have added a new paragraph in Section 4.3 discussing the practical considerations of high-albedo wall materials like aluminum (albedo 0.9). The new paragraph (2) addresses glare, durability, and maintenance, noting that frequent rainfall in tropical savanna climates may mitigate soiling, but maintenance costs and visual comfort remain factors. It suggests semi-reflective coatings (e.g., white paints, albedo ~0.8) or textured surfaces to balance thermal benefits with practical constraints.

Comment 2: The study fixes emissivity at 0.9 for all materials to isolate albedo effects. However, emissivity varies across real-world materials (e.g., glass vs. concrete). A brief sensitivity analysis or acknowledgment of how emissivity variability might influence UTCI could enhance the technical rigor.
Response: We appreciate the reviewer’s suggestion to address emissivity variability. To enhance rigor, we have added a new paragraph in Section 2.2 (Surface Material Selection) presenting the basic grounds of the albedo values selection. Additionally, Section 4.3 (Limitations and Future Research) was updated to note this limitation that fixing emissivity, though useful for isolating the effects of albedo variation, simplifies radiative transfer but may not capture material-specific variations. The revised section 4.3 further proposes future sensitivity analyses to explore emissivity’s impact on UTCI.

Comment 3: The non-linear relationship between wall albedo and UTCI (peaking at intermediate albedo values) is intriguing but not fully explored. A deeper technical discussion on the radiative balance (e.g., interplay of shortwave reflection, longwave emission, and material transparency like glass) or thermal mass differences (e.g., aluminum vs. concrete) might clarify the underlying physics driving this pattern.
Response: We agree that a deeper discussion of the non-linear wall albedo effects strengthens the manuscript. We have added a new paragraph in Section 4.2 (Beyond Albedo: The Role of Material Properties) discussing the non-linear UTCI response (peaking at albedo 0.3–0.45) due to material-specific radiative behaviors (e.g., glass’s high transmission, aluminum’s reflectivity) and thermal mass differences (e.g., aluminum vs. concrete).

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Abstract

• The abstract could be more concise, as it is currently too lengthy. Clarifying the words "obscure their impact," "challenging assumptions," and "advocating simulations" may be useful.

Introduction

• For the first hundred words, the Introduction goes on almost too broad generalities. Reduce back on repeated UHI explanations.

•  

  Although critical perspective is lacking, literature is widely referenced. The authors hardly ever question or combine the listed works.

•  

  It references Myhre and Myhre (2003) for radiative forcing but fails to precisely relate that idea to pedestrian-level comfort—a vertical jump from atmospheric physics to urban planning.

• The first fails to discover an original research question. Although no hypotheses or conceptual framework is tested, the goals are clear

Material and Methods

• Other studies (such as Akure, Nigeria) have model calibration drawn from them without any validation for the current urban geometry. That reduces reliability of the study
• The “72-hour simulation” is only described as running from September 1–3 with no justification. Why these dates? Why this time window?
• While 117 receptor points sound impressive, there’s no mention of spatial interpolation or error bars—this gives the illusion of precision without accounting for spatial uncertainty.

Results

• Despite using 16 models and many receptor points, the effect sizes are underwhelming (e.g., 0.44°C UTCI mean change for ground albedo). Is this practically significant?
• Too many plots (e.g., Figure 6 and 7) lack proper discussion. The “non-linear” pattern is mentioned, but no deeper attempt is made to model this statistically (e.g., polynomial regression or spline).

Discussions

• The use of “transparency shifts heat stress indoors rather than outdoors” is speculative. No indoor simulations were done.
• The part is lacking in theoretical depth. No effort is made to address radiative balance equations or basic thermal perception models. All depends on the outputs of ENVI-met.
• Statements like “glass produced less reflective heat than opaque materials” lack measured evidence (no radiant flux data is given).
• “Strategic material selection” is a good takeaway but repeated too often without design application examples.

Limitation and Conclusion

• Repetition of “future research should…” becomes generic. Instead, author please try to propose concrete future scenarios (e.g., modeling plaza layouts, or accounting for diurnal shading effects).
• The conclusion reflects an overview of findings rather than a synthesis. Try to give a synthesis and highlight the important findings
•  

Comments on the Quality of English Language

Can be improved further

Author Response

Response to Reviewer 2

Abstract
Comment: The abstract could be more concise, as it is currently too lengthy. Clarifying the words “obscure their impact,” “challenging assumptions,” and “advocating simulations” may be useful.
Response: We thank the reviewer for suggesting improvements to the Abstract’s conciseness and clarity. We have streamlined the Abstract and changed the word choice for more clarity. The revised Abstract reads: “High-albedo materials are promoted to mitigate heat stress… These findings prioritize reflective wall materials for sustainable heat mitigation…”

Introduction
Comment 1: For the first hundred words, the Introduction goes on almost too broad generalities. Reduce back on repeated UHI explanations.
Response: We acknowledge the reviewer’s concern about excessive generality in the Introduction. We have condensed the first paragraph of Section 1.1 (Urban Heat and Thermal Comfort in Tropical Areas, page 2) to reduce repetition of Urban Heat Island (UHI) and thermal discomfort concepts, combining sentences into a focused statement.

Comment 2: Although critical perspective is lacking, literature is widely referenced. The authors hardly ever question or combine the listed works.
Response: We appreciate the reviewer’s suggestion to enhance critical synthesis in the literature review. In Section 1.2 (Influence of Surface Materials on Thermal Comfort), we added comparative and synthetic points drawn from the literature; for instance, after Huang et al., we note Erell et al.’s caution about high-albedo pavements increasing pedestrian heat stress... The revised literature review also emphasizes wall albedo’s potential for sustainable urban design, noting underexplored interactions with ground albedo.

Comment 3: It references Myhre and Myhre (2003) for radiative forcing but fails to precisely relate that idea to pedestrian-level comfort—a vertical jump from atmospheric physics to urban planning.
Response: We thank the reviewer for pointing out the need to clarify the link between Myhre and Myhre and pedestrian comfort. In Section 1.3 (Research Gaps and Goals), we added a precision linking the atmospheric phenomenon to the local/pedestrian comfort, namely that tropical regions have stronger radiative forcing due to high solar insolation, reducing surface absorption of solar radiation and lowering surface temperatures. This decrease in surface heating and longwave emission directly mitigates radiant heat exposure for pedestrians, influencing the Universal Thermal Climate Index (UTCI), at pedestrian level.

Comment 4: The first fails to discover an original research question. Although no hypotheses or conceptual framework is tested, the goals are clear.
Response: We agree that an explicit research question enhances the Introduction’s clarity. In Section 1.3 (page 4), we added a research question to highlight the study’s originality and sustainability focus: “…How do ground and wall albedo independently and interactively affect pedestrian thermal comfort (UTCI) in tropical savanna urban canyons, and what material combinations optimize sustainable urban design for heat mitigation and livability?” This aligns with the study’s parametric goals and addresses the reviewer’s concern.

Materials and Methods
Comment 1: Other studies (such as Akure, Nigeria) have model calibration drawn from them without any validation for the current urban geometry. That reduces reliability of the study.
Response: We appreciate the reviewer’s concern about calibration reliability. In Section 2.5 (Software Reliability and Parameterization), we clarified that the calibration based on Morakinyo et al. [40] in Akure, Nigeria, is appropriate due to its tropical savanna climate and high validation metrics (R² > 0.96). We noted ENVI-met’s robustness across urban morphologies supports its application to our deep canyon geometry (H/W = 2.0), though site-specific validation was not conducted due to the hypothetical design. Nevertheless, the limitation of the hypothetical parametric method is discussed in Section 4.3.

Comment 2: The “72-hour simulation” is only described as running from September 1–3 with no justification. Why these dates? Why this time window?
Response: We thank the reviewer for requesting justification for the simulation period. In Section 2.5, it was clarified that the simulation was calibrated based on reports by Morakinyo et al. validation in Akure, Nigeria, for the relatively higher correlation and lower errors. In the revised version, we added that September 1–3 represents peak summer conditions in tropical savanna climates, characterized by high solar radiation and dry season weather. The 72-hour duration (48 hours for stabilization, 24 hours for analysis) follows standard ENVI-met protocols.

Comment 3: While 117 receptor points sound impressive, there’s no mention of spatial interpolation or error bars—this gives the illusion of precision without accounting for spatial uncertainty.
Response: We acknowledge the reviewer’s concern about spatial uncertainty. In Section 2.6 (Output Processing), we clarified that the 117 receptors were distributed via stratified sampling to minimize spatial uncertainty. The previous manuscript did not insert error bars as standard errors are significantly low. Nevertheless, the revised version has inserted relevant data in the appendix to support the spatial resolution of the receptors.

Results
Comment 1: Despite using 16 models and many receptor points, the effect sizes are underwhelming (e.g., 0.44°C UTCI mean change for ground albedo). Is this practically significant?
Response: We appreciate the reviewer’s question about practical significance. In Section 4.1 (Ground versus Wall Albedo), we added a statement explaining that the small ground albedo effect (0.44°C UTCI) is practically significant, as it suggests limited benefits from high-albedo pavements, redirecting focus to cost-effective wall materials for sustainable urban design. The revised text reads: “The small ground albedo effect (0.44°C UTCI) is practically significant, as it suggests limited benefits from high-albedo pavements…”

Comment 2: Too many plots (e.g., Figure 6 and 7) lack proper discussion. The “non-linear” pattern is mentioned, but no deeper attempt is made to model this statistically (e.g., polynomial regression or spline).
Response: We thank the reviewer for noting the need for deeper discussion of plots. In Section 3.2 (UTCI Variation According to Wall Materials), we expanded the discussion of Figures 6 and 7, referencing polynomial regressions to model the non-linear UTCI response to wall albedo.

Discussions
Comment 1: The use of “transparency shifts heat stress indoors rather than outdoors” is speculative. No indoor simulations were done.
Response: We agree that the indoor heat stress claim was speculative. In Section 4.2 (Beyond Albedo: The Role of Material Properties), we removed the statement and replaced it with: “Instead, glass transmits most shortwave radiation… but its high transmission reduces pedestrian-level heat stress compared to opaque materials.” This revision avoids speculation and is supported by literature.

Comment 2: The part is lacking in theoretical depth. No effort is made to address radiative balance equations or basic thermal perception models. All depends on the outputs of ENVI-met.
Response: We acknowledge the reviewer’s suggestion for greater theoretical depth. In Section 4.2, we added more discussions on the non-linear UTCI response to wall albedo, covering shortwave reflection, longwave emission, transparency, and thermal mass, supported by literature references. We avoided radiative balance equations, as they are beyond the scope for our urban design audience, focusing instead on UTCI’s physiological basis.

Comment 3: Statements like “glass produced less reflective heat than opaque materials” lack measured evidence (no radiant flux data is given).
Response: We thank the reviewer for pointing out the need for evidence. In Section 4.2, we clarified glass’s radiative behavior, noting that UTCI reductions with high-albedo walls align with reduced longwave emission. A new sentence reads: “While radiant flux data was not directly measured, the UTCI reductions with high-albedo walls align with reduced longwave emission…”

Comment 4: “Strategic material selection” is a good takeaway but repeated too often without design application examples.
Response: We agree that “strategic material selection” was overused. In Sections 4.1 and 4.2 (pages 10–11), we consolidated its mentions and added specific design examples, such as pairing reflective wall coatings (albedo ~0.8) with low-albedo asphalt (albedo ~0.2) in Section 4.1, and semi-reflective coatings or textured aluminum in Section 4.2.

Limitation and Conclusion
Comment 1: Repetition of “future research should…” becomes generic. Instead, author please try to propose concrete future scenarios (e.g., modeling plaza layouts, or accounting for diurnal shading effects).
Response: We appreciate the reviewer’s suggestion for specific future scenarios. In Section 4.3 (Limitations and Future Research), we revised the future research paragraph to propose concrete scenarios, such as modeling shallow canyons, open plazas, diurnal shading from trees, and finer temporal resolutions (e.g., 30-minute UTCI outputs).

Comment 2: The conclusion reflects an overview of findings rather than a synthesis. Try to give a synthesis and highlight the important findings.
Response: We thank the reviewer for suggesting a stronger synthesis. In Section 5 (Conclusion,, we revised the text to synthesize key findings, emphasizing wall albedo’s primacy, the minimal ground albedo effect, and the counteractive interaction, with implications for sustainable urban design.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript uses ENVI-met for parametric numerical simulations and distinguishes the effects of surface and wall reflectivity. It highlights the importance of wall reflectivity on pedestrian thermal comfort and suggests that high surface reflectivity may offset the cooling effect of high-reflectivity walls. The topic is of some practical significance and innovation, and the experimental design is fairly systematic. However, there are still several shortcomings in the experimental design that require in-depth revisions and improvements.

1.Experimental Design

(1) The current experimental scenario design is quite simplistic and does not cover the diversity of real-world urban environments. The study only considers one typical deep urban canyon scenario (Aspect ratio = 2) and lacks exploration of different urban structures and other urban forms. This omission makes it difficult to reflect the heterogeneity of real cities, limiting the generalizability of the conclusions.

(2) The experimental data lacks site validation specific to the region of interest. Although the paper references validation data from other regions (e.g., Thailand), there is no field observation or validation conducted for the representative area of the study region. This may introduce uncertainty and limitations in the results.

(3) The rationality of the measurement point distribution is not explained. While 117 measurement points cover different street directions, it is unclear whether they include dynamic shaded areas (such as under tree canopies or between buildings) or open squares. This raises concerns about the representativeness of the data.

(4) The introduction of experimental materials is brief. The paper only provides reflectivity and emissivity values for the surface and wall materials but overlooks critical thermophysical parameters such as thermal conductivity, specific heat capacity, and other key indicators. These parameters are crucial for understanding the thermal exchange properties of urban materials.

(5) The assumption of fixed emissivity for materials is not rigorous. The manuscript assumes an emissivity of 0.9 for all materials, but in reality, metals (e.g., aluminum) have much lower emissivity than this, and the difference from materials like concrete (0.88-0.94) is significant.

(6) The temporal resolution of UTCI calculations is insufficient. The manuscript only extracts data at hourly intervals from 6:00 to 18:00 (12 time periods), but solar radiation in tropical regions fluctuates dramatically around noon. A 1-hour time step may obscure transient peaks, which could influence the conclusions of the study.

2.Results Analysis

(1) The statistical analysis of the results remains superficial. Most of the results are analyzed using simple linear regression, neglecting nonlinear relationships (such as the nonlinear effects of wall reflectivity on UTCI), interaction effects, or deeper multivariate statistical analysis. This approach fails to fully capture the mathematical relationships and does not adequately account for spatial heterogeneity.

(2) The discussion of the results is not sufficiently in-depth. The discussion mainly emphasizes the importance of wall reflectivity on pedestrian thermal comfort but does not thoroughly explore its underlying physical mechanisms.

3.Other Issues

(1) There is an error in the section numbering. For example, "5.1. Limitations and Future Research" appears in section 4 (Discussion).

(2) In Figures 6 and 7, the color differentiation between different data points is weak, with overlaps that make it difficult to read and interpret the figures.

Author Response

Response to Reviewer 3

Experimental Design
Comment 1.1: The current experimental scenario design is quite simplistic and does not cover the diversity of real-world urban environments. The study only considers one typical deep urban canyon scenario (Aspect ratio = 2) and lacks exploration of different urban structures and other urban forms. This omission makes it difficult to reflect the heterogeneity of real cities, limiting the generalizability of the conclusions.
Response: We acknowledge the reviewer’s concern about the single geometry’s generalizability. In Section 4.3 (Limitations and Future Research, we added a limitation noting that the focus on a deep canyon (H/W = 2.0) may not generalize to shallower canyons or open plazas. We propose future research on diverse urban geometries to address this.

Comment 1.2: The experimental data lacks site validation specific to the region of interest. Although the paper references validation data from other regions (e.g., Thailand), there is no field observation or validation conducted for the representative area of the study region. This may introduce uncertainty and limitations in the results.
Response: We thank the reviewer for raising the issue of site-specific validation. In Section 2.5 (Software Reliability and Parameterization), we clarified that our parametric study uses hypothetical scenarios, leveraging Morakinyo et al.’s validation in a similar tropical savanna climate (R² > 0.96), making site-specific validation unnecessary in a hypothetical context. Nevertheless, in Section 4.3, we acknowledged that potential uncertainty in site-specific applicability.

Comment 1.3: The rationality of the measurement point distribution is not explained. While 117 measurement points cover different street directions, it is unclear whether they include dynamic shaded areas (such as under tree canopies or between buildings) or open squares. This raises concerns about the representativeness of the data.
Response: We appreciate the reviewer’s request for clarity on receptor distribution. In Section 2.6 (Output Processing), we added that the 117 receptors were distributed via stratified sampling across N-S streets, E-W streets, and courtyards to capture varied solar exposure, including shaded and unshaded areas. This addresses representativeness concerns.

Comment 1.4: The introduction of experimental materials is brief. The paper only provides reflectivity and emissivity values for the surface and wall materials but overlooks critical thermophysical parameters such as thermal conductivity, specific heat capacity, and other key indicators. These parameters are crucial for understanding the thermal exchange properties of urban materials.
Response: We acknowledge the reviewer’s point about thermophysical parameters. In Section 2.2 (Surface Material Selection), we added a sentence noting that thermal conductivity and specific heat were not investigated, as the study focuses on albedo, with future research suggested to explore these properties.

Comment 1.5: The assumption of fixed emissivity for materials is not rigorous. The manuscript assumes an emissivity of 0.9 for all materials, but in reality, metals (e.g., aluminum) have much lower emissivity than this, and the difference from materials like concrete (0.88–0.94) is significant.
Response: We thank the reviewer for highlighting the emissivity assumption. In Section 2.2 , in the context of the parametric simulation method employed, we added a comment explaining the fixed emissivity (0.9) as a control to isolate the albedo parameter [17], but noting real-world variability (e.g., aluminum ~0.2–0.3, glass ~0.83–0.90) [44]. Section 4.3 was updated to acknowledge this limitation and suggest sensitivity analyses.

Comment 1.6: The temporal resolution of UTCI calculations is insufficient. The manuscript only extracts data at hourly intervals from 6:00 to 18:00 (12 time periods), but solar radiation in tropical regions fluctuates dramatically around noon. A 1-hour time step may obscure transient peaks, which could influence the conclusions of the study.
Response: We appreciate the reviewer’s suggestion for finer temporal resolution. In Section 2.6, we justified hourly UTCI outputs as standard ENVI-met practice, balancing computational efficiency and accuracy for diurnal trends, with low standard errors (0.07–0.2, Appendix A). We acknowledge that a 30-minute resolution could capture transient solar peaks, proposing this for future research in Section 4.3.”

Results Analysis
Comment 2.1: The statistical analysis of the results remains superficial. Most of the results are analyzed using simple linear regression, neglecting nonlinear relationships (such as the nonlinear effects of wall reflectivity on UTCI), interaction effects, or deeper multivariate statistical analysis. This approach fails to fully capture the mathematical relationships and does not adequately account for spatial heterogeneity.
Response: We thank the reviewer for noting the need for deeper statistical analysis. In Section 3.2 (UTCI Variation According to Wall Materials), we emphasized polynomial regressions (R² = 0.80–0.88) to model non-linear wall albedo effects and added a preliminary analysis of ground-wall albedo interactions (R² < 0.05), reinforcing wall albedo’s dominance.

Comment 2.2: The discussion of the results is not sufficiently in-depth. The discussion mainly emphasizes the importance of wall reflectivity on pedestrian thermal comfort but does not thoroughly explore its underlying physical mechanisms.
Response: We agree that a deeper exploration of physical mechanisms enhances the discussion. In Section 4.2), we added a detailed qualitative explanation on wall albedo’s dominance, covering shortwave reflection, longwave emission, transparency (e.g., glass), and thermal mass (e.g., aluminum vs. concrete), supported by relevant literature references.

Other Issues
Comment 3.1: There is an error in the section numbering. For example, “5.1. Limitations and Future Research” appears in section 4 (Discussion).
Response: We thank the reviewer for identifying the numbering error. We reviewed the manuscript’s structure and corrected the error.

Comment 3.2: In Figures 6 and 7, the color differentiation between different data points is weak, with overlaps that make it difficult to read and interpret the figures.
Response: We appreciate the reviewer’s feedback on figure readability. The pointed figures were revised with added transparency to the data points, and they will be available in high resolution for more readability.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

This article focuses on strategies for mitigating the Urban Heat Island (UHI) effect and systematically reviews the application of Decision Support Systems (DSS), Multi-Criteria Decision Making (MCDM), and Fuzzy Theory in this field. Through bibliometric analysis, it reveals the current research trends and gaps. The topic is closely related to the forefront issues of urban climate adaptation and sustainable development, with clear practical significance and academic value. The paper demonstrates scientific rigor and innovation but requires improvements in structural clarity, data presentation details, and the depth of discussion to enhance both scientific accuracy and practical guidance.

1. The format of the keywords needs to be adjusted, replacing the comma with a semicolon between “Ground material” and “Wall materials” to meet the journal’s specifications.

2. The rationale for selecting ground reflectance (0.2–0.8) and wall reflectance (0.05–0.90) should be clarified. For instance, why is the range of wall reflectance much wider than that of the ground? Was the typical value of actual materials referenced? It is recommended to cite industry standards or existing literature for support.

3. The paper does not explain why the emissivity is fixed (such as typical building material properties), while the emissivity of different materials (such as glass and concrete) may vary. Relevant physical property parameters should be supplemented with their sources or verification methods.

4. Wall reflectance significantly affects UTCI, but the physical mechanism behind its dominant role needs further explanation.

5. It is recommended to add the practical significance of the research for actual urban planning, for example, "The study provides empirical evidence for the optimal selection of wall materials in urban design under tropical savanna climates."

6. It is recommended to add the spatial distribution logic of the 117 monitoring points (e.g., stratified sampling according to street orientation or shading coverage).

7. It is suggested to directly label significance symbols (such as *P<0.05) or confidence intervals in Figures 6 and 7.

8. In the discussion section, it is recommended to analyze the physical mechanism where high ground albedo may offset the cooling effect of walls (e.g., reflected radiation from the ground is secondarily reflected to pedestrian height by the walls), and compare it with existing literature for verification.

Author Response

Response to Reviewer 4

Comment 1: The format of the keywords needs to be adjusted, replacing the comma with a semicolon between “Ground material” and “Wall materials” to meet the journal’s specifications.
Response: We thank the reviewer for noting the keyword formatting issue. We revised the keywords section to use semicolons, ensuring compliance with journal specifications.

Comment 2: The rationale for selecting ground reflectance (0.2–0.8) and wall reflectance (0.05–0.90) should be clarified. For instance, why is the range of wall reflectance much wider than that of the ground? Was the typical value of actual materials referenced? It is recommended to cite industry standards or existing literature for support.
Response: We appreciate the reviewer’s request for clarity on albedo ranges. In Section 2.2 (Surface Material Selection), we added a new paragraph explaining the ground albedo range (0.2–0.8) and wall albedo range (0.05–0.90) based on the ENVI-met material library, common urban materials, and compatibility with the study’s setup. The wider wall range reflects the diversity of facade materials (e.g., glass to aluminum) compared to pavements’ functional constraints.

Comment 3: The paper does not explain why the emissivity is fixed (such as typical building material properties), while the emissivity of different materials (such as glass and concrete) may vary. Relevant physical property parameters should be supplemented with their sources or verification methods.
Response: We thank the reviewer for addressing the emissivity assumption. In Section 2.2 (page 5), we justified fixing emissivity at 0.9 as a control to isolate albedo effects, typical for concrete and pavements, but noted variability (e.g., aluminum ~0.2–0.3, glass ~0.83–0.90). Section 4.3 acknowledges this limitation and suggests future sensitivity analyses.

Comment 4: Wall reflectance significantly affects UTCI, but the physical mechanism behind its dominant role needs further explanation.
Response: We agree that explaining wall albedo’s physical mechanism is crucial. In Section 4.2, we added a detailed qualitative radiative model describing how high-albedo walls (e.g., aluminum, albedo 0.9) reduce UTCI by reflecting shortwave radiation upward and minimizing longwave emission, contrasted with intermediate-albedo materials (e.g., concrete).

Comment 5: It is recommended to add the practical significance of the research for actual urban planning, for example, "The study provides empirical evidence for the optimal selection of wall materials in urban design under tropical savanna climates."
Response: We appreciate the reviewer’s suggestion to highlight practical significance. In Section 5 (Conclusion), we added a statement emphasizing the study’s empirical evidence for prioritizing reflective wall materials in urban planning to optimize thermal comfort and reduce cooling costs in tropical savanna climates.

Comment 6: It is recommended to add spatial distribution logic for the 117 monitoring points (e.g., stratified sampling according to street orientation or shading coverage).
Response: We thank the reviewer for requesting clarity on receptor distribution. In Section 2.6, we added that the 117 receptors were distributed via stratified sampling across N-S streets, E-W streets, and courtyards to capture varied solar exposure, including shaded and unshaded areas.

Comment 7: It is suggested to directly label significance symbols (such as *P<0.05) or confidence intervals in Figures 6 and 7.
Response: We appreciate the suggestion; in the revised version of the manuscript, authors have aggregated all statistical details to the appendix.

Comment 8: In the discussion section, it is recommended to analyze the physical mechanism where high ground albedo may offset the cooling effect of walls (e.g., reflected radiation from the ground is secondarily reflected to pedestrian height by the walls), and compare it with existing literature for verification.
Response: We thank the reviewer for suggesting a deeper analysis of the ground-wall albedo interaction. In Section 4.1 (Ground versus Wall Albedo), we added a detailed explanation of how high-albedo grounds reflect shortwave radiation directly to pedestrians and trigger secondary reflections from reflective walls, increasing UTCI and reducing wall cooling effectiveness.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

This revised manuscript presents an integrated and technically sound evaluation with considerable improvements from its previous version. However, while the manuscript improves in clarity, organization, and scientific depth, there are still some significant concerns about methodological rigor, interpretation, and presentation that require further enhancement before publish:

1. The "originality" is substantially undermined by an overreliance on previously known ENVI-met simulations and well-established albedo ranges. The authors should explain how their analysis improves previous ENVI-met-based albedo simulation studies.
2. The choice of emissivity = 0.9 for all surfaces is too straightforward. While the purpose was to "control longwave effects," it could undermine reality particularly for metallic versus porous surfaces. This reduces confidence in the absolute UTCI values.
3. The physical mechanism of how “high transmittance glass reduces pedestrian heat stress” needs quantitative support, e.g., radiant flux comparisons.
4. Polynomial regression used is justified, but no model diagnostics (e.g., RMSE, AIC) are reported.
5. For practitioners, what does it mean to pair low ground albedo with high wall albedo in terms of material choices, costs, and lifecycle maintenance in tropical cities like Kuala Lumpur or Accra?

Author Response

Reviewer 2

Comments and Suggestions for Authors

This revised manuscript presents an integrated and technically sound evaluation with considerable improvements from its previous version. However, while the manuscript improves in clarity, organization, and scientific depth, there are still some significant concerns about methodological rigor, interpretation, and presentation that require further enhancement before publish:

1. The "originality" is substantially undermined by an overreliance on previously known ENVI-met simulations and well-established albedo ranges. The authors should explain how their analysis improves previous ENVI-met-based albedo simulation studies.

Response: Thank you for your feedback regarding the use of ENVI-met simulations in our study. We understand the concern about originality, Our study advances the theoretical understanding by (1) pointing out the almost irrelevance of ground albedo under the climatic settings of the study, (2) shifts the attention to wall material albedo, and (3) the non-linear pattern which suggest on the one hand that project based or case-specific studies are necessary, and on the research front further study is necessary for encapsuling the multi-parameter interplay with other material properties. We hope this clarifies the focus and originality of our work.

 

1. The choice of emissivity = 0.9 for all surfaces is too straightforward. While the purpose was to "control longwave effects," it could undermine reality particularly for metallic versus porous surfaces. This reduces confidence in the absolute UTCI values.

Response: Thank you for your feedback. We appreciate your recognition of our intent to isolate albedo’s effect on UTCI. We agree that this experimental simplification cannot exhaustively account for all real-world materials, but it nevertheless enhances the theoretical clarity of albedo-driven trends and ensures a ‘relative’ comparison. The trade-offs of this approach have been acknowledged in Section 4.3. Authors would argue that exhaustively/absolutely capturing real-world implications on this matter would certainly go beyond albedo and emissivity variability, which is one of the implications that can be understood from the paper’s discussions and conclusions.

 

1. The physical mechanism of how “high transmittance glass reduces pedestrian heat stress” needs quantitative support, e.g., radiant flux comparisons.

Response: Thank you for this suggestion. We’ve added quantitative support in the results section showing that: “W1 exhibited a mean radiant temperature (MRT) of 52.82°C, which is approximately 11.3% lower than concrete (W2, albedo 0.3, MRT 59.52°C) and 7.8% lower than moderately insulated walls (W3, albedo 0.45, MRT 57.31°C). This reduction is driven by differences in radiant fluxes: W1’s shortwave (SW) flux was 151.33 W/m², a decrease of ~16.1% compared to W2 (180.39 W/m²) and ~14.3% compared to W3 (176.58 W/m²), while its longwave (LW) flux was 471.32 W/m², ~1.4% lower than W2 (477.75 W/m²) and ~0.3% lower than W3 (472.64 W/m²), as illustrated in Figure 8. These reductions in radiant fluxes directly contribute to a lower UTCI for W1 compared to W2 and W3, as high transmission minimizes the reflection and absorption of solar radiation, reducing both the reflected shortwave and emitted longwave radiation at pedestrian level (~1.5 m).”.

 

1. Polynomial regression used is justified, but no model diagnostics (e.g., RMSE, AIC) are reported.

Response: We value your input on regression diagnostics. Authors agreed with the reviewers’ suggestion to insert the polynomial fitting. In our understanding it serves to capture the albedo-UTCI pattern observed under the experimental settings of the study. Nevertheless, RMSE and AIC (useful for observation versus prediction analysis) are less applicable here, as our study uses ENVI-met output (based on previously validated calibration with R² > 0.90 [38], the relative error metrics having been published in the referenced paper) for pattern analysis but not prediction. Authors in the discussion and conclusions advocate multi-parameter modeling for future predictive efforts, keeping this paper within the scope of its objectives.

1. For practitioners, what does it mean to pair low ground albedo with high wall albedo in terms of material choices, costs, and lifecycle maintenance in tropical cities like Kuala Lumpur or Accra?

Response: Thank you for highlighting this practical need. Section 4.3 addresses this, suggesting that: “the practical implementation of such high wall albedo requires consideration of durability, maintenance, and visual comfort. For instance, Aluminum’s high reflectivity may cause glare, potentially affecting pedestrian comfort, and soiling can reduce albedo over time [17,47]. In tropical savanna climates, frequent rainfall may mitigate dust accumulation, and maintenance costs also remain a factor. For practical purposes, urban designers should balance thermal benefits with practical constraints, potentially using semi-reflective coatings (e.g., white paints, albedo ~0.8) or textured surfaces to minimize glare while retaining cooling potential [16].”

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

After revision, the quality of the paper has been significantly improved. However, there are still several issues that need to be addressed in order to further enhance the article. I encourage the authors to make additional revisions. The specific issues are as follows:

1.Experimental Design.

(1) The assumption that the emissivity of all experimental materials is fixed at 0.9 is unreasonable and lacks scientific basis. The paper assumes that all materials in the experiment have an emissivity of 0.9, but in reality, metals such as aluminum have much lower emissivity values, which differs significantly from materials like concrete. Although the limitations of this assumption are discussed in the paper, the experimental process could be improved by incorporating experiments with varying emissivity values or performing sensitivity analysis. Additionally, according to the revision feedback, reference [17] has not been cited in section 2.2 to support the experimental parameter setup.

(2) There is confusion in defining the parameters of experimental materials. The albedo range for wall surfaces (0.05-0.90) includes transparent materials, such as glass (with a transmittance of 90%). Albedo typically applies to opaque materials, while the "albedo" of glass is actually its reflectivity. The primary thermal effect of glass is driven by transmission, which does not align with the definition of albedo.

2.Logic.

(1) The title of section 1.3, “Research Gaps and Goals,” creates ambiguity, as the content discusses the current research limitations and the objectives of the study. This may confuse readers. It is recommended to revise the title for clarity.

(2) The research background or methodology section lacks a detailed introduction to the ENVI-met software. The advantages and limitations of ENVI-met in simulating urban microclimates have not been fully explained, nor is there any justification for choosing this software over other simulation tools.

3.Formatting Details.

(1) Most of the figure and table captions in the paper do not follow the required format. Please adjust them according to the journal’s guidelines.

(2) Figure 1 has formatting issues, as the figure and its number are separated.

(3) The resolution of Figure 7 is insufficient, making the fitting equation and R² values unclear and difficult for readers to interpret.

(4) There is an error in the table numbering. According to the revised manuscript, Figure 6 has been deleted, but the paper still references Figure 6 multiple times.

(5) The color of the numbers in Table 2 is inconsistent, and there are formatting issues with the "Bias" column. Please check and correct them.

(6) There is no need to add a period at the end of the keywords section.

Author Response

Reviewer 3

Comments and Suggestions for Authors

After revision, the quality of the paper has been significantly improved. However, there are still several issues that need to be addressed in order to further enhance the article. I encourage the authors to make additional revisions. The specific issues are as follows:

1.Experimental Design.

(1) The assumption that the emissivity of all experimental materials is fixed at 0.9 is unreasonable and lacks scientific basis. The paper assumes that all materials in the experiment have an emissivity of 0.9, but in reality, metals such as aluminum have much lower emissivity values, which differs significantly from materials like concrete. Although the limitations of this assumption are discussed in the paper, the experimental process could be improved by incorporating experiments with varying emissivity values or performing sensitivity analysis. Additionally, according to the revision feedback, reference [17] has not been cited in section 2.2 to support the experimental parameter setup.

Response: We understand your concern at the core of which is the variability of Emissivity. but we must acknowledge that the rigor of the parametric approach requires that certain parameters are assumed fixed (in this case, the emissivity) while observing the individual impact of selected parameter one at a time. Varying emissivity would expand the parametric scenarios beyond this study’s scope, as other properties also vary in reality, a point addressed in Section 4.3 and our multi-parameter discussion.

Reference [17] is now cited in Section 2.2 to support parameter setup.

 

(2) There is confusion in defining the parameters of experimental materials. The albedo range for wall surfaces (0.05-0.90) includes transparent materials, such as glass (with a transmittance of 90%). Albedo typically applies to opaque materials, while the "albedo" of glass is actually its reflectivity. The primary thermal effect of glass is driven by transmission, which does not align with the definition of albedo.

Response: Great point. Thank you for highlighting the parameter definition concern for glass. We acknowledge that albedo traditionally applies to opaque surfaces and the nuance was overlooked, In our parametric design, we use it as a proxy for reflectivity in the case of Glass material to ensure consistency and readability, Subsection 2.2. (ii. Wall materials) is revised to clarify that.

 

2.Logic.

(1) The title of section 1.3, “Research Gaps and Goals,” creates ambiguity, as the content discusses the current research limitations and the objectives of the study. This may confuse readers. It is recommended to revise the title for clarity.
Response: thanks, the title is revised to “current research limitations and study objectives”.

(2) The research background or methodology section lacks a detailed introduction to the ENVI-met software. The advantages and limitations of ENVI-met in simulating urban microclimates have not been fully explained, nor is there any justification for choosing this software over other simulation tools.

Response: thank you for this suggestion, further justification is added at the beginning of the subsection 2.5: “ENVI-met, a high-resolution 3D microclimate simulation software, was selected for this study due to its robust capability to model complex urban environments, including radiative, convective, and conductive heat exchanges at pedestrian level (1.5 m). Its advantages include detailed parameterization of surface albedo, shortwave (SW) and longwave (LW) radiant fluxes, and mean radiant temperature (MRT), which are critical for assessing albedo effects on thermal comfort [34,38]. Unlike other userfriendly simulation tools such as RayMan or SOLWEIG, etc., ENVImet has a detailed material interaction modeling capability and multi-layer urban canopy representation, making it ideal for our hypothetical experiment [38]”.

3.Formatting Details.

(1) Most of the figure and table captions in the paper do not follow the required format. Please adjust them according to the journal’s guidelines.

(2) Figure 1 has formatting issues, as the figure and its number are separated.

(3) The resolution of Figure 7 is insufficient, making the fitting equation and R² values unclear and difficult for readers to interpret.

(4) There is an error in the table numbering. According to the revised manuscript, Figure 6 has been deleted, but the paper still references Figure 6 multiple times.

(5) The color of the numbers in Table 2 is inconsistent, and there are formatting issues with the "Bias" column. Please check and correct them.

(6) There is no need to add a period at the end of the keywords section.

Response: Thank you for your attention to details. The formatting errors have been fixed.

Author Response File: Author Response.pdf