PCLM-D-26-00070

Diurnal asymmetry in heat stress intensification across Bangladesh, 1985–2024: Accelerated nighttime warming and emerging urban risk

PLOS Climate

Dear Dr. Kamruzzaman,

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Kind regards,

Lakshmi Kumar T V

Academic Editor

PLOS Climate

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Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.-->

Reviewer #1: Partly

Reviewer #2: Yes

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-->2. Has the statistical analysis been performed appropriately and rigorously?-->

Reviewer #1: Yes

Reviewer #2: Yes

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-->3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: No

Reviewer #2: Yes

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-->4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Climate does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #2: Yes

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-->5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: The manuscript entitled “Diurnal asymmetry in heat stress intensification across Bangladesh, 1985–2024: Accelerated nighttime warming and emerging urban risk” presents a policy-relevant assessment of heat stress in Bangladesh using the Universal Thermal Climate Index (UTCI) derived from ERA5-HEAT at 0.25° resolution (≈27 km), for 1985–2024. It clearly emphasizes diurnal asymmetry, showing stronger increases in nighttime and early-morning heat stress than in daytime extremes in multiple major cities over Bangladesh. However, several issues currently limit robustness and reproducibility of the results, most critically the internal inconsistencies in reported trend magnitudes, insufficient methodological detail for city extraction and statistical testing, and lack of validation analysis. I recommend major revisions. The manuscript needs to address the specific comments below.

Specific Comments

1. All results rely on reanalysis derived from UTCI. ERA5-HEAT may be appropriate, but heat stress trends in Bangladesh should be cross checked with independent observations where possible (e.g., station T/RH/wind for major cities, or gridded observed temperature/humidity proxies).

2. The manuscript reports inconsistent warming levels: the abstract gives +0.03°C decade⁻¹ for UTCIₘᵢₙ, while the results state grid-cell Sen slopes of +0.1 to +0.4°C decade⁻¹, and the two-period climatology indicates an approximately 1.0–1.5°C shift over 20 years.

3. The methods stated that city UTCI metrics were extracted from ERA5-HEAT grid cells corresponding to each city’s administrative boundary. However, city-level results are not reproducible because the manuscript does not report the number of grid cells per city, the weighting scheme, or the sensitivity of results to grid selection at 0.25°. Provide explicit city masks, cell counts, and a sensitivity analysis.

4. The abstract claims city intensification is linked to urban heat-island effects. The study area section similarly asserts that Dhaka has a strong UHI effect. However, the manuscript later acknowledges a key limitation: ERA5-HEAT at 0.25° cannot reliably capture neighborhood-scale microclimatic differences (e.g., variations due to urban density and building layout). Therefore, attributing city-level intensification to UHI is not supported by the current methods. The manuscript must either implement an urban–rural contrast analysis or revise statements to avoid causal attribution.

5. The manuscript conceptually emphasizes reduced nighttime cooling capacity during the study period. However, the manuscript does not quantify reduced nighttime cooling in the results.

6. Captions are generally good (e.g., Fig 2 and Fig 4 descriptions) but ensure every mapped trend figure states clearly whether slopes are per decade, and how significance is computed (MMK details).

7. Chittagong/Chattogram should be used consistently throughout the manuscript.

8. The manuscript uses a five-class subset (0–46°C) tailored to Bangladesh, with Very Strong Heat Stress defined as UTCI 38–46°C. Provide a histogram or exceedance plot of UTCIₘₐₓ and UTCIₘᵢₙ to confirm whether the values >46°C truly do not occur (or are negligible).

Reviewer #2: The manuscript presents a valuable and timely assessment of diurnal heat stress trends using high-resolution UTCI data, with particular emphasis on the increasing role of nighttime heat exposure. The topic is scientifically relevant and contributes to the growing body of literature on compound and persistent heat stress. However, major revision is required to enhance clarity, robustness, and scientific impact. The novelty of the study, particularly regarding diurnal asymmetry and its implications, should be more explicitly articulated in the context of existing research. In addition, the manuscript would benefit from a more rigorous treatment of uncertainties associated with ERA5-HEAT data, including potential biases and spatial limitations. The interpretation of stronger nighttime warming (UTCIₘᵢₙ trends) requires deeper mechanistic explanation, supported by relevant physical processes such as boundary layer dynamics and urban heat storage. Furthermore, the role of urban heat island effects should be quantitatively assessed rather than qualitatively described. Finally, the manuscript should strengthen its discussion of policy relevance by linking findings to health risks and actionable adaptation strategies. Addressing these points will significantly improve the manuscript’s scientific rigor and applicability.

1. The manuscript presents long-term UTCI analysis; however, the novel contribution is not explicitly defined. The concept of diurnal asymmetry requires clearer positioning within existing heat stress literature.

Required Revision: Clearly state the unique contribution (e.g., nighttime recovery loss, 24-hour heat stress framework, city-scale evidence).

2. The use of ERA5-HEAT (0.25° resolution) introduces spatial and structural uncertainties, which are acknowledged but not quantified.

Required Revision: Include uncertainty analysis, dataset comparison, and discussion of potential bias in reanalysis products.

3. The stronger increase in UTCIₘᵢₙ compared to UTCIₘₐₓ is reported, but physical mechanisms are insufficiently explained.

Required Revision: Provide explanation based on:

• Urban heat storage

• Boundary layer dynamics

• Reduced nocturnal cooling

4. Urban heat amplification is described qualitatively; however, no quantitative attribution is performed.

Required Revision: Include urban–rural comparison or statistical attribution to isolate UHI effects.

5. Although impacts are discussed, quantitative linkage to health risk or labor productivity is limited.

Required Revision: Integrate exposure thresholds and actionable recommendations for Heat Action Plans.

MINOR COMMENTS (Quality Improvements)

1. Ensure uniform use of:

• UTCIₘᵢₙ / UTCIₘₐₓ / UTCIₘₑₐₙ

• Heat stress vs thermal stress

2. Figures are informative but lack clear interpretation in text.

Required Revision: Add concise explanations highlighting key findings.

3. Trend results lack:

• Confidence intervals

• Magnitude interpretation

4. Some sections are descriptive rather than analytical.

Required Revision: Improve scientific tone with precise, quantitative statements.

5. The connection between results and discussion needs improvement.

Required Revision: Strengthen logical transitions and interpretation flow.

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Reviewer #1: No

Reviewer #2: No

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Diurnal asymmetry in heat stress intensification across Bangladesh, 1985–2024: Accelerated nighttime warming and emerging urban risk

PCLM-D-26-00070R1

Dear Dr Kamruzzaman,

We are pleased to inform you that your manuscript 'Diurnal asymmetry in heat stress intensification across Bangladesh, 1985–2024: Accelerated nighttime warming and emerging urban risk' has been provisionally accepted for publication in PLOS Climate.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow-up email from a member of our team.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

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Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Climate.

Best regards,

Lakshmi Kumar T V

Academic Editor

PLOS Climate

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Additional Editor Comments (if provided):

Reviewer Comments (if any, and for reference):

Reviewer's Responses to Questions

-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #1: All comments have been addressed

Reviewer #3: All comments have been addressed

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-->2. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.-->

Reviewer #1: Yes

Reviewer #3: Yes

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-->3. Has the statistical analysis been performed appropriately and rigorously?-->

Reviewer #1: Yes

Reviewer #3: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #3: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Climate does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #3: Yes

**********

-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1:  The manuscript has improved substantially, and I appreciate that the authors’ great efforts to revising the structure, clarifying methodological details and improving the statistical analyses. Overall, the revised manuscript is much stronger than before. I have no further comments and believe the manuscript is suitable for publication.

Reviewer #3:  General Minor Comments

The manuscript presents a timely and scientifically relevant assessment of diurnal heat stress trends in Bangladesh using a robust 40-year UTCI dataset. The revisions have substantially improved the clarity, methodological transparency, and interpretation of the findings.

The authors have adequately clarified the concept of diurnal asymmetry and strengthened the discussion of nighttime heat-stress intensification, which represents a valuable contribution to the heat-risk literature in South Asia.

The additional explanations regarding ERA5-HEAT limitations, urban heat island attribution, and uncertainty considerations improve the scientific rigor and help avoid overinterpretation of the results.

The figures, tables, and supporting analyses are generally clear and effectively communicate the spatial and temporal evolution of heat stress across Bangladesh and its major cities. Only minor editorial proofreading may be beneficial during production to ensure consistency in terminology, notation, and formatting throughout the manuscript.

Overall, the study is well-structured, methodologically sound, and provides important evidence for climate adaptation planning, public health preparedness, and urban resilience in rapidly warming regions. I believe the manuscript is suitable for publication in PLOS Climate after routine editorial processing.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review?  If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.-->

Reviewer #1: No

Reviewer #3: No

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