the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Jun 2025
Assessment of the vulnerability of buildings destroyed during postfire debris flow events in Kule village, Yajiang County, China
Abstract. Debris flows are frequently triggered by rainstorms after wildfires and pose severe threats to the lives of downstream residents and buildings in mountainous regions. However, there has been limited focus on developing a comprehensive framework to assess the physical vulnerability of buildings to postfire debris flows. This study presents a quantitative approach for establishing a physical vulnerability model on the basis of the observed building damage features and simulated debris flow intensity values. Detailed field surveys were conducted in Kule village, Yajiang County, to analyse the characteristics of postfire debris flows and establish a building damage database. Numerical simulations using the FLO-2D model were performed to reproduce the debris flow process and quantify the debris flow intensity, including the flow depth, flow velocity, impact pressure, momentum flux, overturning moment, and relative burial height. Physical vulnerability curves were developed for brick–concrete buildings and compared with those obtained in previous studies, and the differences in vulnerability curves, intensity indicators, and functional models were examined. The results revealed that the lognormal cumulative distribution function (LNCDF) model provides the highest statistical significance in terms of the relative error and prediction accuracy. The momentum flux demonstrated greater sensitivity in distinguishing different damage categories, whereas the impact pressure provided more precise vulnerability index predictions. The proposed physical vulnerability model can be used to evaluate the structural resistance of buildings to debris flows in wildfire-affected areas, thus providing a systematic foundation for formulating risk management and mitigation strategies.
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Status: final response (author comments only)
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CC1: 'Comment on egusphere-2025-772', wei wang, 26 Jun 2025
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AC1: 'Reply on CC1', Jiangang Chen, 28 Jun 2025
Dear Reviewer
We appreciate your positive and constructive comments on our manuscript. Thank you very much for your recognition our manuscript, and for considering our article interesting and suitable. Thank you very much for providing valuable suggestions to help us improve the manuscript. After studying the comments carefully, we have made every effort to respond and revise your professional guidance and suggestions. If there are any suggestions in the future, we are very willing to make timely modifications. Our primary task is to meet the standards of the journal, and we sincerely hope that this research can be considered. We would like to express our great appreciation once again to you for comments and recognition on our paper. For detailed point-by-point responses and modifications, please refer to the supplementary materials.
Sincerely yours
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AC1: 'Reply on CC1', Jiangang Chen, 28 Jun 2025
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CC2: 'Comment on egusphere-2025-772', Xiaogang Guo, 10 Jul 2025
This is an interesting and valuable paper on debris flow disaster mitigation in mountainous regions. It contributes meaningfully to enhancing disaster prevention and mitigation capabilities in these areas. The study offers important insights into advancing post-fire debris flow assessments, refining vulnerability models, and guiding emergency evacuation strategies. I sincerely appreciate the authors for sharing such inspiring and impactful work. Overall, the work is quite detailed, but it needs to improve the conciseness and logic of its expression, the following is several comments and suggestions that may help improve the manuscript.
Abstract
- Lines 21-22, the background and research questions are too disconnected, lacking a summary of the current state of research within a broader context, which would help highlight the existing research gaps.
- Authors emphasize using the quantitative approach, but the results did not show any number or quantitative result. Please give the quantitative description.
- In theabstract, authors should highlight the significance of this research.
Introduction
- Lines 42-66, Shorten the introduction to highlight the current status of the research in this paper and the problems that need to be solved. Directly point out why the debris flow disasters after wildfiresare worthy of being focused on and then the vulnerability is significant…
- Line 57: Suggest changing "continuous curve" to "monotonically increasing curve".
- Line 75, means “previous study”?
- Lines 77-98, please use the logic sentences to connect your reviewing work, don’t list the researchers one-by-one. And you should finallyconclude why you choose FLO-2D to simulate.
- Line 88: It is suggested to clarify that the "relative intensity" here refers to "relative burial height". This can be consistent with the article.
- Lines 137-144: This paragraph in the introduction should not be treated as a separate paragraph and should be added to the end of the previous paragraph as a follow-up explanation. It is recommended to adjust it.
- Line 138: Suggest changing "thereby burning"to ", burning".
Study area
- Authors should pay attention to the paper framework: introduction, methods and materials, results, discussion, conclusion. So, studyarea should be in the section of Methods and materials. And I suggest combine study area and field investigation section.
- Line 191, please provide the right information of China map, change it.
- Line 269, as for the 2.3 Debris flow peak dischargecalculation, please give the main formula and list the derivation process to the Supplementary file.
- Line 213 (Fig 3): Capitalize "Flo-2D" consistently as "FLO-2D" in text within the figure.
- Lines 240-242: I suggest changing the expression of slope here. Generally, slope is described as steep or gentle.Suggest replacing “high” and “lower” with “steeper” and “gentler”.
- Line 326: Please clearly define nas Manning's coefficient and use the symbol "n" to express it uniformly in Eq. 7.
- Line 326: Similarly, please clearly define K in Eq. 7.
- Line 399: Suggest changing 'power law' to 'power-law'.
- Line 405:Please define "V" explicitly in Eq. 15 is " vulnerability value (0-1)".
Results
- Line 426:Please add the annotation "in G1 gully" to the title of Figure 7.
- Line 463: What’s the meaningof P = 2?
- Lines 484-642: I greatly appreciate the author's extensive and in-depth exploration in the discussion section. They have done a lot of meaningful and commendable work on different indicators of debris flow intensity and vulnerability functions, as well as comparisons with previous research. This can provide important reference value for future researchers.
Discussion
- In the section 5.1, authors should shorten the pages, just focus on the simulation result, don’t show the calculation process, and don’t list 3 subtitles.
- Change the order of 5.1.4 and 5.2; limitation and future work should be a separate
- Lines 490-523 & Fig 13-14: In-depth comparative analysis of intensity indicators (sensitivity vs. precision) is highly valuable and a key contribution.
- Table 5, The expression in the second column is inaccurate. Please modify it. Adjust the format of the content in the table.
- Lines 587-589: I suggest simplifying the expression of this paragraph and changing it to “Table 6 provides the existing vulnerability function models, including Logical, Weibull, Exponential, LNCDF and Avrami functions”.
- Line 643: The authors' honest discussion of limitations enhances this excellent paper. I commend their approach to complex challenges and anticipate future work.
- Lines 689: These suggestions on emergency response and evacuation strategies for disasters are valuable for local residents.
- 17, Modify the display legend of the elevation.
Conclusion and references
- Line 772:Add DOI number to references.
- Check the “Figure”or “Fig” used in the paper, the format should be uniform. Unify the format of the tables in the full paper.
- Further refine the conclusion section.
- Line 745, revise the author’s names.
- Check the references’style, just like “-” and “–”, the space in the middle of the name abbreviation.
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AC2: 'Reply on CC2', Jiangang Chen, 21 Jul 2025
Dear Editors and Reviewers,
We are sincerely grateful for your constructive feedback on our manuscript (egusphere-2025-772) and your recognition of its value. We deeply appreciate your thoughtful comments and actionable suggestions, which are instrumental in enhancing the quality of our work. The praise and positive feedback you provided are a great honor and significant encouragement to our team. We have carefully addressed all reviewer comments through thorough revisions to meet the journal's standards. Should any further suggestions arise, we remain fully committed to making timely modifications. Our primary goal is to ensure the manuscript aligns with the journal's expectations, and we hope it merits favorable consideration.
Firstly, we are truly honored and grateful that you found our study "interesting and valuable" for advancing debris flow disaster mitigation in mountainous regions. Your recognition that it meaningfully contributes to enhancing disaster prevention capabilities and offers important insights into post-fire debris flow assessments, vulnerability modeling, and emergency evacuation strategies is incredibly motivating. We especially appreciate your kind acknowledgment of the study's impact and detailed nature. We greatly appreciate your recognition and high praise of our discussion section and the proposed emergency responses. We fully agree with your assessment that promoting this work as a reference for future research is worthwhile, and we are pleased that you see its potential value for local residents.
Secondly, we sincerely appreciate your insightful comments and constructive suggestions for improving the manuscript. Following your guidance, we have carefully revised and supplemented the relevant sections. Once again, we extend our profound gratitude for your insightful review and endorsement.
Finally, thank you once again for your valuable suggestions and recognition, which have significantly strengthened our study. Should any omissions remain in our revisions, we would welcome your further corrections. Please accept our profound gratitude for your mentorship throughout this revision process. Our point-by-point responses and detailed modifications are provided in the supplementary materials.
Sincerely yours,
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RC1: 'Comment on egusphere-2025-772', Anonymous Referee #1, 30 Aug 2025
This is an interesting and valuable paper on post-fire debris flow disaster in mountainous regions. After I carefully read the paper, I think this paper is quite detailed; however, it still needs to improve the conciseness and logic of its expression. Some comments and suggestions are listed and hope it’s helpful for the authors to improve the manuscript.
1. Abstract: Two points
(1) Further refinement the abstract is needed, and the verbose sentences need to be rewritten.
(2) Reduce procedural descriptions and appropriately increase quantitative results.
2. Introduction: Three points
(1) Reduce the total word count of the introduction.
(2) Line 137-144, move to “Section 2 Study area”.
(3) Add a clear statement of the aims.
3. Study area: One point
(1) Merge the contents of the following two sections: Section 2 and Section 3.1 and 3.2.
4. Methods: One point
(1) Retain the introduction and verification of numerical simulation methods (Section 3.3) and Development of empirical vulnerability models for buildings (Section 3.4).
5. Results: Two points
(1) Merge Figure 7 and Figure 8, Revise the expressions in the text.
(2) Revise the title of Section 4.2 and 4.3, to highlight the characteristics of this part.
6. Discussion: Further refine the content, now it’s about 15 pages.
7. Conclusion: Further refine the conclusions.
8. References: Refer to the submission instructions, check the format and add DOI.
9. Check the Figs and the title of the Fig.
10. The final version of the MS should be reviewed by a native English speaker.
Citation: https://doi.org/10.5194/egusphere-2025-772-RC1 -
AC3: 'Reply on RC1', Jiangang Chen, 22 Sep 2025
Dear Referee #1
We are sincerely grateful for your encouraging recognition of our study’s value and for your constructive suggestions, which have greatly strengthened our manuscript. We deeply appreciate your thoughtful comments and actionable suggestions, which are instrumental in enhancing the quality of our work. The praise and positive feedback you provided are a great honor and significant encouragement to our team. We have carefully addressed all your comments through thorough revisions to improve the conciseness and logical flow of the paper. Your insightful feedback has been instrumental in enhancing the quality of our work. Should any further adjustments be needed, we remain fully committed to making timely revisions. We deeply appreciate your guidance throughout this process and hope the manuscript meets the journal’s standards.
Sincerely yours,
The following are specific responses, and our point-to-point responses are also provided in the form of a list in the supplementary materials.
- Comments: This is an interesting and valuable paper on post-fire debris flow disaster in mountainous regions. After I carefully read the paper, I think this paper is quite detailed; however, it still needs to improve the conciseness and logic of its expression. Some comments and suggestions are listed and hope it’s helpful for the authors to improve the manuscript.
Response: We are deeply grateful for your exceptionally generous and insightful feedback on our manuscript. Your kind words and positive assessment have been a tremendous encouragement to our entire team. Firstly, we are truly honored that you considered our study "interesting and valuable" in advancing debris flow disaster mitigation in mountainous regions. Thank you for recognizing the impact and thoroughness of our work—it is especially rewarding to know that our research resonates with experts like you, whose perspectives are highly valued in the field. Secondly, we sincerely appreciate your insightful comments and constructive suggestions for improving the conciseness and logic of expression. Following your guidance, we have carefully revised and supplemented the relevant sections. Our specific point-by-point responses and modifications are detailed below. Finally, Thank you once again for your valuable suggestions and recognition. We are deeply grateful for your encouraging feedback and actionable advice, which have significantly strengthened our study. Should any aspects still require further refinement, we warmly welcome your additional guidance. Please accept our profound gratitude for your mentorship throughout this revision process.
- Comments: 1. Abstract: Two points (1) Further refinement the abstract is needed, and the verbose sentences need to be rewritten. (2) Reduce procedural descriptions and appropriately increase quantitative results.
Response: (1) Thank you for your valuable suggestion. Following your professional guidance, we have thoroughly revised the abstract to improve clarity and eliminate verbosity, restructuring long sentences for directness. Thank you again for your valuable comments and assistance. (2) Thank you very much for your valuable comments. Based on your valuable suggestion, we also recognize that that the original version overemphasized the process; consequently, we have significantly increased the emphasis on our quantitative results by incorporating key data to better highlight our main findings and further highlight this expression more clearly. Thank you again for your suggestions on enhancing the expression.
- Comments: 2. Introduction Three points (1) Reduce the total word count of the introduction. (2) Line 137-144, move to “Section 2 Study area”. (3) Add a clear statement of the aims.
Response: (1) Thank you very much for your valuable comments on the Introduction section. Your suggestions have helped us make it more concise and logically coherent. We have streamlined the entire section by consolidating sentences with similar meanings to achieve more compact expression and removing redundant background information. Through these measures, the total word count of the introduction has been reduced, resulting in a sharper focus. Thank you again for your suggestions on enhancing the expression of our paragraphs. (2) Thank you for your careful guidance and suggestions. We greatly appreciate this suggestion regarding placement. You are absolutely correct that the description of the study area's specific characteristics is out of place in the Introduction and more naturally belongs in the dedicated "Study Area" section. We have moved the content from lines 137-144 in its entirety to Section 2 (Study Area). We have also polished the transition to ensure it integrates smoothly with the surrounding text in its new location. Thank you again for your valuable advice and guidance. (3) We would like to express our gratitude for your valuable suggestions. Under your professional guidance, we have added and modified a clearer and more concise statement of the research aims at the end of the introduction section, which explicitly outlines the primary objectives of our study. Thank you again for this important feedback and suggestions.
- Comments: 3. Study area: One point (1) Merge the contents of the following two sections: Section 2 and Section 3.1 and 3.2.
Response: (1) Thank you for your valuable suggestion. As your suggested, we have consolidated the content from the original Section 2 (Study Area) and Sections 3.1 & 3.2 into a single and comprehensive section. This new section provides a more coherent and streamlined description of the geographical context and the characteristics of debris flow channels. Thank you again for these constructive suggestions regarding the manuscript's structure.
- Comments: 4. Methods: One point (1) Retain the introduction and verification of numerical simulation methods (Section 3.3) and Development of empirical vulnerability models for buildings (Section 3.4).
Response: (1) Thank you for valuable suggestion and guidance. We have retained the core methodological components as your instructed. The content from the original Section 3.3 (introduction and verification of numerical simulation methods) and Section 3.4 (Development of empirical vulnerability models for buildings) now forms the main body of our revamped "3. Methods" section. This ensures the methodological description is focused on the most critical and innovative aspects of our work. Thank you again for your valuable comments.
- Comments: 5. Results: Two points (1) Merge Figure 7 and Figure 8, Revise the expressions in the text. (2) Revise the title of Section 4.2 and 4.3, to highlight the characteristics of this part.
Response: (1) Thank you for this valuable suggestion. According to your suggestion, we have merged Figure 7 and Figure 8, which will facilitate a more direct and effective comparison of the results. Furthermore, we have thoroughly revised the corresponding text in the Results section. All previous references to the separate Figure 7 and Figure 8 have been updated to direct the reader to the new and combined figure. Thank you again for your careful guidance. (2) Thank you for your valuable suggestion. We have revised the titles to more accurately and prominently reflect the core findings and applications presented: The original title 4.2 and 4.3 has been revised to “4.2 Development of an intensity-vulnerability model for debris flow” and "4.3 Model application: intensity Prediction and spatial vulnerability assessment for the G2 gully". Thank you again for helping us improve our expression.
- Comments: 6. Discussion: Further refine the content, now it’s about 15 pages.
Response: Thank you for your valuable suggestion. We have critically reviewed the entire section to eliminate redundancy and consolidate related arguments. The focus has been sharpened to provide a more concise and impactful interpretation of the key results, their direct implications and compared with existing literature. Thank you again for your suggestion.
- Comments: 7. Conclusion: Further refine the conclusions.
Response: We greatly appreciate your valuable suggestions. According to your suggestion, we have thoroughly revised the Conclusion section to ensure it is precise and impactful. Thank you again for your guidance and assistance.
- Comments: 8. References: Refer to the submission instructions, check the format and add DOI.
Response: Thank you for this important reminder. The DOI for all references has been added. Thank you again for your careful suggestion.
- Comments: 9. Check the Figs and the title of the Fig.
Response: Thank you for your careful suggestion. We will check and unify it. Thank you again for your careful inspection.
- Comments: 10. The final version of the MS should be reviewed by a native English speaker.
Response: Thank you for your valuable suggestion. we have engaged the professional editing services to thoroughly review and polish the entire manuscript language. The final version has been meticulously checked for grammar, spelling, syntax, and overall fluency to ensure it meets the high standards required for publication. Thank you again for your suggestion.
Finally, we are profoundly grateful for your thorough review and expert guidance. Thank you again for your high recognition of our manuscript, which has given us great confidence to strengthen this study. we greatly appreciate your suggestions for helping us improve our manuscript, and we hope these improvements meet the journal’s standards for publication. Should further clarifications be needed, we are fully committed to addressing them promptly.
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AC3: 'Reply on RC1', Jiangang Chen, 22 Sep 2025
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RC2: 'Comment on egusphere-2025-772', Anonymous Referee #2, 14 Dec 2025
General comments:
The manuscript presents a case study of building vulnerability to postfire debris flows in Kule village, using field investigation, FLO-2D simulations and empirical vulnerability functions. The postfire debris flow appears quit different physical characteristics and dynamic behavior comparing with normal debris flow, which will cause it to have different destructive characteristics. This manuscript has noticed the variations in the destructive characteristics, and has studied the vulnerability of buildings under the influence of postfire debris flows after a fire. It is novel and has practical value for disaster risk reduction.
The current description shows that the authors conducted a field investigation in the burned area, derived the necessary physical parameters and then ran the model. In the analysis, the authors first select debris-flow intensity measures and then fit intensity–damage relationships with different functional forms, concluding that the LNCDF model performs best among the tested options. Readers would like to know whether one can also run this model after conducting a field investigation in non-fire areas and getting the corresponding parameters? I hope manuscript can descript it point clearly. In addition, there are several issues in the description of the study area, figure labelling and English usage. I therefore recommend minor revision. The followings are detailed comments for reference.
Specific comments:
- The FLO-2D parameters calibrated for the G1 event are directly transferred to the G2 gully, while only the DEM and design peak discharges are changed. However, the G1 and G2 gullies may differ in channel morphology, roughness and postfire sediment conditions. This assumption of parameter homogeneity between the two gullies is not explicitly discussed, and its potential impact on the predicted intensities and damage scenarios is unclear. I recommend that the authors, where possible, compare the simulated results for G2 with other available post-event, in order to support the transferability of the calibrated parameter set and enhance confidence in the model results.
- The authors compare different functional forms and conclude that LNCDF provides the best fit between debris-flow intensity and building vulnerability. However, it remains unclear why LNCDF performs best, and what aspects of postfire debris flows make the intensity-damage relationship different from that of “normal” debris flows. I recommend that the authors expand the discussion to analyze the physical or empirical reasons behind the superior performance of LNCDF and to highlight the characteristic features of postfire debris-flow propagation and hazard formation, as well as the specific damage mechanisms of buildings subjected to postfire debris flows.
Technical corrections:
- In Sect. 3.2 the authors only present the calculation of peak discharges, whereas Fig. 6 shows full discharge hydrographs, with identical peak duration for all return periods. Please clarify how these hydrographs were derived and whether assuming the same peak duration for different return periods is reasonable.
- In the methods, the debris flow is described as wide-graded, and Fig. 4f shows boulders with diameters on the order of 0.5 m, whereas Fig. 4i indicates a maximum grain size of less than 10 cm. Please check whether there is an inconsistency between the field observations and the grain-size distribution and correct or explain if necessary.
- L11 “University of Chinese Academy Sciences” should be “University of Chinese Academy of Sciences”
- L32-34 The term “statistical significance” is normally used together with p-values and hypothesis testing, not with relative error or prediction accuracy.
- L61 When listing existing vulnerability models, it would be helpful to briefly summarize their performance or main limitations, rather than only enumerating them.
- Both the introduction and the discussion contain long paragraphs that mainly list references. I suggest condensing these lists and focusing more on synthesizing the key messages and identifying gaps, instead of extensive citation catalogues.
- Please reorganize the English expression regarding the article's primary objectives in the line 146-155. For example, use the present tense and “to do …” for your objectives.
- L137 It should be “On 15 March, 2024”. Please standardize all date expressions throughout the manuscript.
- L178 Please check whether it is appropriate to describe Yajiang County as having a “subtropical monsoon climate”.
- L178-181 Please specify for which period the average rainfall of 166.1 mm is calculated. Moreover, the statement “the average rainfall reaches 166.1 mm, accounting for more than 70% of the total annual precipitation” is not consistent with the long-term annual precipitation of 600-1200 mm.
- L474 There seems to be an error in Fig. 10d: the label for flow velocity and design frequency suggests P = 2%, but from the context it may be P = 1%. A similar issue appears in the title of Appendix B, where the panel (b) “Design frequency P = 1%” should likely be “P = 2%”. Please check all labels carefully.
- L588 “logical functions” should be “logistic functions”
- L592 The definition and calculation of R², MRE and other performance indices should be described in the Methods section rather than in the Discussion. Please consider moving the description to the methodological part for clarity.
Citation: https://doi.org/10.5194/egusphere-2025-772-RC2 -
AC4: 'Reply on RC2', Jiangang Chen, 09 Jan 2026
Dear Referee #2
We are sincerely grateful for your recognition and encouragement of our study’s value and its novelty and practical value for disaster risk reduction. Thank you for giving us the opportunity and recommend minor revision. The praise and positive feedback you provided are a great honor and significant encouragement to our team. We deeply appreciate your invaluable suggestions and meticulous guidance, which have greatly strengthened our manuscript. We have carefully reviewed your specific comments and technical corrections, and have addressed each one thoroughly in the revised manuscript. Following your careful guidance, all necessary corrections and clarifications have been made to improve the accuracy, clarity, and overall quality of the presentation. Should any further adjustments be needed, we remain fully committed to making timely revisions. We deeply appreciate your guidance throughout this process and hope the manuscript meets the journal’s standards. Please accept our deepest gratitude for your mentorship throughout this revision process.
Sincerely yours,
The following are specific responses, and our point-to-point responses are also provided in the form of a list in the supplementary materials.Comment 1: General comments: The manuscript presents a case study of building vulnerability to postfire debris flows in Kule village, using field investigation, FLO-2D simulations and empirical vulnerability functions. The postfire debris flow appears quit different physical characteristics and dynamic behavior comparing with normal debris flow, which will cause it to have different destructive characteristics. This manuscript has noticed the variations in the destructive characteristics, and has studied the vulnerability of buildings under the influence of postfire debris flows after a fire. It is novel and has practical value for disaster risk reduction. The current description shows that the authors conducted a field investigation in the burned area, derived the necessary physical parameters and then ran the model. In the analysis, the authors first select debris-flow intensity measures and then fit intensity–damage relationships with different functional forms, concluding that the LNCDF model performs best among the tested options. Readers would like to know whether one can also run this model after conducting a field investigation in non-fire areas and getting the corresponding parameters? I hope manuscript can descript it point clearly. In addition, there are several issues in the description of the study area, figure labelling and English usage. I therefore recommend minor revision. The followings are detailed comments for reference.
Response 1: Dear Reviewer, with utmost gratitude, we wish to express our profound appreciation for your invaluable suggestions and meticulous guidance.
Firstly, thank you very much for your recognition and encouragement of our manuscript. We appreciate your recognition of its novelty and practical value for disaster risk reduction. Thank you for giving us the opportunity and recommend minor revision, which has given us great confidence to work hard to address the existing problems.
Secondly, we are deeply grateful for your professional guidance and invaluable suggestions, which have greatly assisted us to improve the clarity and presentation of our work. Thank you for raising this valuable question regarding the model's applicability to non-fire areas, which is indeed important for readers. You are correct to highlight this point. The core methodology presented in this study—integrating post-event field investigation, physics-based numerical simulation (FLO-2D), and statistical vulnerability modeling (LNCDF)—constitutes a transferable framework. Specifically, the LNCDF vulnerability function model itself is applicable to both fire and non-fire contexts, as demonstrated in previous studies on conventional debris flows (Kean et al., 2019; Luo et al., 2023). The primary distinction when applying this framework lies in the context-specific inputs and corresponding parameters. For non-fire areas, key differences would arise in the sediment source conditions and hydrological response due to intact vegetation, and consequently, the simulated debris flow intensities. These differences would lead to different fitted parameter values within the LNCDF model, reflecting the altered hazard characteristics. However, this does not affect the applicability of the statistical model form itself. The overall analytical framework remains valid and can be adapted by using appropriate, site-specific inputs. We will clarify this important point in the revised manuscript (in the Discussion section) to explicitly state the adaptability of the methodological framework and the context-specific nature. Regarding the other issues you mentioned concerning the description of the study area, figure labelling, and English usage, we sincerely apologize for these oversights. We have carefully reviewed your specific comments and technical corrections, and have addressed each one thoroughly in the revised manuscript. Following your careful guidance, all necessary corrections and clarifications have been made to improve the accuracy, clarity, and overall quality of the presentation. Your constructive feedback has been invaluable in helping us refine and strengthen the paper.
Finally, thank you again for your valuable suggestion and your recognition. Your suggestions are very helpful and make our manuscript more organized and complete, and improved the scientific quality. Thank you for investing your time and effort in providing feedback. We strive to provide detailed responses and careful revisions, and sincerely appreciate your valuable suggestions and professional guidance. If we had any omissions in the modifications, we hope to get your corrections. Please accept our deepest gratitude for your mentorship throughout this revision process.
References:
Luo, H. Y., Zhang, L. M., Zhang, L. L., He, J., & Yin, K. S. (2023). Vulnerability of buildings to landslides: The state of the art and future needs. Earth-Science Reviews, 238, 104329.
Kean, J. W., Staley, D. M., Lancaster, J. T., Rengers, F. K., Swanson, B. J., Coe, J. A., … Lindsay, D. N. (2019). Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment. Geosphere, 15(4), 1140–1163.Comment 2: Specific comments:1. The FLO-2D parameters calibrated for the G1 event are directly transferred to the G2 gully, while only the DEM and design peak discharges are changed. However, the G1 and G2 gullies may differ in channel morphology, roughness and postfire sediment conditions. This assumption of parameter homogeneity between the two gullies is not explicitly discussed, and its potential impact on the predicted intensities and damage scenarios is unclear. I recommend that the authors, where possible, compare the simulated results for G2 with other available post-event, in order to support the transferability of the calibrated parameter set and enhance confidence in the model results.
Response 2: Thank you for your valuable and helpful suggestions. We fully understand your concern that the transfer of model parameters between different gullies requires clear explanation and discussion to reduce the uncertainty in the prediction results. In accordance with your recommendations, we have made the following additions and revisions to the manuscript to clarify the methodology, discuss limitations, and strengthen the argument.
First, we have provided a full explanation of the practical constraints and research objectives of this study. The G2 catchment is a potentially hazardous gully where no post-fire debris flow has yet occurred, and therefore no post-event observational data from G2 itself is available for direct model validation. The primary purpose of including G2 in our simulations is precisely to enable a comparative risk assessment with the adjacent G1 catchment, where a disaster has already occurred. This approach aims to reveal the compound, bilateral threat that both gullies pose to the downstream Kule Village, thereby providing a more comprehensive integrated vulnerability assessment for this community.
In response to your concerns regarding the feasibility of parameter transfer, we have added a supplementary explanation in the Methods section. This explicitly states the rationale and fundamental assumptions behind applying the parameter set calibrated for G1 to G2, which are based on the following considerations: (1) G1 and G2 are spatially adjacent and exhibit similarities in terms of geological setting, soil type, vegetation, catchment hydrological characteristics, fire history, and field-observed surface material composition; (2) Using the same parameter set, validated against the G1 event, is essential to ensure that the simulation results for both catchments are on a consistent basis, which is crucial for a fair evaluation of their relative hazard to the same community.
Furthermore, following your guidance, we have substantially expanded the Discussion section. We have added an explicit discussion emphasizing the uncertainties associated with the assumption of parameter similarity and its potential impact on predicted intensities and damage scenarios. To address your suggestion to seek "other available post-event data" for comparison in order to support parameter transferability, we systematically collected and cited published case studies of debris flows occurring in similar geological and post-fire environments (e.g., Gong et al., 2025; He et al., 2024). We conducted a comparative analysis, matching the order of magnitude and range of key macro-indicators from our G2 simulations (such as velocity range, typical deposition depth, and inundation area) with the actual observations recorded in field surveys of other similar gullies within the region. This analysis verifies that our simulation results are consistent, both in magnitude and physics, with observational data from analogous hazard events. These lines of evidence strengthen confidence in the applicability of our parameter set within the study area and in the credibility of the predicted scenarios for G2. Thank you again for your valuable advice and professional guidance, which helped us improve our manuscript.
References:
Gong, X., Zhou, Y., Hu, X., He, K., & Wang, J. (2025). Spatiotemporal distribution characteristics of post-fire debris flows during the first rainy season following Yajiang Fire, Sichuan, China: X. Gong et al. Landslides, 1-16.
He, K., Hu, X., Wu, Z., Zhong, Y., Zhou, Y., Gong, X., & Luo, G. (2024). Preliminary analysis of the wildfire on March 15, 2024, and the following post-fire debris flows in Yajiang County, Sichuan, China.Comment 3: 2. The authors compare different functional forms and conclude that LNCDF provides the best fit between debris-flow intensity and building vulnerability. However, it remains unclear why LNCDF performs best, and what aspects of postfire debris flows make the intensity-damage relationship different from that of “normal” debris flows. I recommend that the authors expand the discussion to analyze the physical or empirical reasons behind the superior performance of LNCDF and to highlight the characteristic features of postfire debris-flow propagation and hazard formation, as well as the specific damage mechanisms of buildings subjected to postfire debris flows.
Response 3: Thank you for your valuable comments and professional guidance. Under your suggestions, we have significantly expanded the “Discussion” section to provide a more in-depth analysis as recommended.
Firstly, we have added a systematic discussion on why the LNCDF is the most appropriate form for vulnerability analysis: 1) Mathematical and Physical Soundness: the LNCDF function curve satisfies the fundamental physical constraints from the origin (0,0) to the saturation point (high intensity, 1), aligning with the physical reality that “no disaster leads to no loss” and that damage tends to saturate under high intensity. Other functional forms (e.g., exponential) cannot mathematically guarantee passage through the origin, representing a theoretical shortcoming. 2) Statistical Robustness and Generalization: The parameter fitting process for the LNCDF is based on the overall distribution of the data rather than point-to-point fitting. This makes the model less sensitive to single, potentially anomalous data points, preventing it from being unduly dominated by outliers and thereby enhancing its robustness. Avoiding overfitting like other functional models, which leads to increased errors and decreased prediction accuracy. Previous studies on the vulnerability analysis of post-fire debris flows and normal debris flows (Kean et al., 2019; Luo et al. (2023) have shown that LNCDF can effectively reduce prediction uncertainty in describing the intensity-damage relationship, further supporting its application.
Secondly, as recommended, we have added a discussion on post-fire debris flows exhibit unique propagation and impact mechanisms compared to "normal" debris flows, primarily due to wildfire-induced watershed changes. These features increase the scatter and uncertainty in the observed intensity-damage relationship, making the LNCDF's statistical properties particularly advantageous: 1) Enhanced Erosion and Flow Composition: Fire increases the proportion of loose, fine particles in surface soil (Ouyang et al., 2023). These are easily entrained, leading to higher solid concentrations, more viscous flows, and a greater tendency for deposition and building inundation. 2) Altered Runoff and Impact Dynamics: Fire damages root systems and reduces slope infiltration capacity, resulting in more pronounced sheet erosion and numerous small runoffs after rainfall. This subjects buildings to multi-directional and uneven impacts, increasing variability in damage even for similar overall flow intensities. Besides, burned basins exhibit lowered rainfall thresholds for debris flow initiation, leading to higher frequency events over extended periods and multiple building damages (Fraser et al., 2022; Ouyang et al., 2023). 3) High temperatures from fire can weaken building envelopes, lowering their initial threshold for withstanding dynamic impact or static deposition loads. The aforementioned mechanisms collectively introduce greater variability and uncertainty into the intensity-damage dataset for post-fire events. The LNCDF model, with its foundation in statistical distribution theory and inherent capacity to accommodate data dispersion, is therefore especially well-suited to robustly characterize the vulnerability relationship arising from these complex and variable post-fire physical processes (Kean et al., 2019). We would like to express our gratitude once again for your valuable suggestions and professional guidance.
References:
Luo, H. Y., Zhang, L. M., Zhang, L. L., He, J., & Yin, K. S. (2023). Vulnerability of buildings to landslides: The state of the art and future needs. Earth-Science Reviews, 238, 104329.
Kean, J. W., Staley, D. M., Lancaster, J. T., Rengers, F. K., Swanson, B. J., Coe, J. A., … Lindsay, D. N. (2019). Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment. Geosphere, 15(4), 1140–1163.
Ouyang, C., Xiang, W., An, H., Wang, F., Yang, W., & Fan, J. (2023). Mechanistic Analysis and Numerical Simulation of the 2021 Post‐Fire Debris Flow in Xiangjiao Catchment, China. Journal of Geophysical Research: Earth Surface, 128(1).
Fraser, A. M., Chester, M. V., & Underwood, B. S. (2022). Wildfire risk, post-fire debris flows, and transportation infrastructure vulnerability. Sustainable and Resilient Infrastructure, 7(3), 188-200.Comment 4: Technical corrections: 1. In Sect. 3.2 the authors only present the calculation of peak discharges, whereas Fig. 6 shows full discharge hydrographs, with identical peak duration for all return periods. Please clarify how these hydrographs were derived and whether assuming the same peak duration for different return periods is reasonable.
Response 4: Thank you for your valuable suggestions and comments. The full discharge hydrographs shown in Fig. 6 were developed using a pentagonal generalized hydrograph method. This approach is commonly employed in debris flow studies where detailed monitoring records are unavailable and has been widely adopted in previous research (Fang et al., 2019; Ding et al., 2023; Zhang et al., 2023). The method constructs the hydrograph shape based on the calculated peak discharge and an estimated total duration. Specifically, the hydrograph is defined such that 1/4 of the peak flow occurs at 1/3 of the total surge duration, and 1/3 of the peak flow occurs at 2/3 of the duration, resulting in a characteristic five-segment shape. We have supplemented the method of flow process line: “The flow process line of debris flow discharge can be obtained by using the generalized pentagon method (Zhang et al., 2023; Ding et al., 2023; Fang et al., 2019).” Regarding the identical peak duration across all return periods, this is an accepted simplification adopted and widely applied in previous studies (Zhang et al., 2023; Ding et al., 2023; Fang et al., 2019). We also recognize the limitations of this method and therefore plan to add a clarification in the discussion section stating that accurately determining debris flow hydrographs still requires actual field monitoring data. Thank you again for your advice and assistance.
References:
Zhang, W., Chen, J., Ma, J., Cao, C., Yin, H., Wang, J., & Han, B. (2023). Evolution of sediment after a decade of the Wenchuan earthquake: a case study in a protected debris flow catchment in Wenchuan County, China. Acta Geotechnica, 18(7), 3905-3926.
Ding, X. Y., Hu, W. J., Liu, F., & Yang, X. (2023). Risk assessment of debris flow disaster in mountainous area of northern Yunnan province based on FLO-2D under the influence of extreme rainfall. Frontiers in Environmental Science, 11, 1252206.
Fang, Q., Tang, C., Chen, Z., Wang, S., & Yang, T. (2019). A calculation method for predicting the runout volume of dam-break and non-dam-break debris flows in the Wenchuan earthquake area. Geomorphology, 327, 201-214.Comment 5: 2. In the methods, the debris flow is described as wide-graded, and Fig. 4f shows boulders with diameters on the order of 0.5 m, whereas Fig. 4i indicates a maximum grain size of less than 10 cm. Please check whether there is an inconsistency between the field observations and the grain-size distribution and correct or explain if necessary.
Response 5: Thank you for this careful observation. You have correctly identified an important distinction between our field observations and the laboratory grain-size analysis, which we should have clarified. Fig. 4f shows large boulders are observed in the channel deposit. the particle-size distribution curve in Fig. 4i was obtained from samples processed using vibrating sieves (measuring range: 0.25–20 mm) and a Malvern laser analyser (measuring range: 0.02–2000 μm). These instruments cannot measure particles at the scale of the observed boulders (e.g., ~0.5 m). Therefore, the curve accurately represents only the portion of the sampled material that falls within the instruments’ measurement range and does not include the largest clasts documented in the field. We have revised the Methods section to explicitly state this point. The following clarifying sentence has been added: “As it is based on sieving and laser analysis of samples, the grain-size curve only includes particles up to 20 mm in size and does not account for the larger boulders (Fig. 4f) documented in the field.” Thank you again for your valuable suggestion, which has helped improve the clarity and precision of our methodology description.Comment 6: 3. L11 “University of Chinese Academy Sciences” should be “University of Chinese Academy of Sciences”
Response 6: Thank you for pointing this out. The institution name has been corrected to “University of Chinese Academy of Sciences” in the manuscript.Comment 7: 4. L32-34 The term “statistical significance” is normally used together with p-values and hypothesis testing, not with relative error or prediction accuracy.
Response 7: Thank you for your valuable suggestion. We agree that “statistical significance” was not the appropriate term in this context. Following your comment, we have revised this expression to more accurately describe the best performance of the LNCDF model in terms of relative error and prediction accuracy, without implying hypothesis testing. The revised text now reads: “The results revealed that the lognormal cumulative distribution function (LNCDF) model achieved the best performance in terms of relative error and prediction accuracy.”. Thank you again for your guidance.Comment 8: 5. L61 When listing existing vulnerability models, it would be helpful to briefly summarize their performance or main limitations, rather than only enumerating them.
Response 8: Thank you for your valuable comment. We have revised the paragraph at line 61 to concisely summarize the common methodological foundation from existing vulnerability analysis, moving from a listing to an integrated statement as suggested. Revised text: “Several statistical method-based studies have been conducted to develop physical vulnerability curves for debris flows on the basis of field data (Lee et al., 2024). They have established curves based on intensity-damage relationships (Fuchs et al., 2007; Totschnig et al., 2011) for specific regions and building types like brick–concrete (BC) and reinforced concrete (RC) structures (Kang and Kim, 2016).” Thank you again for your insightful suggestion, which has helped us synthesize the cited literature into a concise overview of common methodological approaches, thereby providing a clearer context for our study.Comment 9: 6. Both the introduction and the discussion contain long paragraphs that mainly list references. I suggest condensing these lists and focusing more on synthesizing the key
Response 9: Thank you for this important and constructive suggestion regarding our introduction and discussion contain long paragraphs that mainly list references. We agree that excessive listing of references can obscure the key messages and critical gaps in the literature. Following your professional guidance, we have carefully revised both sections with a focus on synthesis and critical analysis rather than citation cataloguing. Specifically: In the introduction, we have restructured the literature review, summarized their collective contributions, and more clearly articulated the research gaps that motivate our work. In the discussion, we have condensed comparative references and strengthened the narrative to directly interpret our results in light of existing knowledge, emphasizing points of agreement, divergence, and the novel implications of our findings. Thank you again for your valuable advice, which has helped us improve the clarity.Comment 10: 7. Please reorganize the English expression regarding the article's primary objectives in the line 146-155. For example, use the present tense and “to do …” for your objectives.
Response 10: Thank you for your valuable suggestions. We have revised the description of the study objectives (lines 146–155) as recommended, now using the present tense and the “to do…” structure to state our aims clearly and concisely. The updated paragraph is provided below for your review: “In this study, the aim is to comprehensively assess the physical vulnerability of buildings damaged during postfire debris flows in Kule village, Yajiang County. The primary objectives are as follows: (1) To analyze the characteristics of postfire debris flows and establish a building damage database through field investigations. (2) To reconstruct debris flow events via FLO‑2D numerical simulations in order to determine debris flow intensity. (3) To develop physical vulnerability curves for BC buildings for assessing the establishment and application of a vulnerability assessment model. (4) To compare the differences in performance among various vulnerability approaches, such as existing intensity indicators, curves, and function models. This work aims to provide insights for advancing postfire debris flow assessments, improving vulnerability models, and guiding emergency evacuation efforts in this region.” Thank you again for your valuable suggestions and professional guidance, which have improved our expression to be clearer.Comment 11: 8. L137 It should be “On 15 March, 2024”. Please standardize all date expressions throughout the manuscript.
Response 11: Thank you for your careful review and valuable advice. According to your suggestion, We have now standardized the format of all dates throughout the manuscript to “Day Month Year”. Specifically, the expressions on Lines 137, 172 and 175 have been revised to “On 15 March, 2024” and “on 10 May”. This ensures consistency in date presentation across the entire text. Thank you again for your helpful comment.Comment 12: 9. L178 Please check whether it is appropriate to describe Yajiang County as having a “subtropical monsoon climate”.
Response 12: Thank you for this insightful comment regarding the climate description. Upon careful consideration and further literature review, it is necessary to provide a more appropriate description. Based on the regional climate expression by He et al. (2024), we have revised the description to specify a “subtropical plateau monsoon climate.” Consequently, we have revised line 178 to: “Yajiang County is located in a subtropical plateau monsoon climate zone (He et al., 2024).” We are grateful for your prompt, which led to this important correction and enhanced the manuscript’s accuracy.
References:
He, K., Hu, X., Wu, Z., Zhong, Y., Zhou, Y., Gong, X., & Luo, G. (2024). Preliminary analysis of the wildfire on March 15, 2024, and the following post-fire debris flows in Yajiang County, Sichuan, China. Landslides, 21(12), 3179-3189.Comment 13: 10. L178-181 Please specify for which period the average rainfall of 166.1 mm is calculated. Moreover, the statement “the average rainfall reaches 166.1 mm, accounting for more than 70% of the total annual precipitation” is not consistent with the long-term annual precipitation of 600-1200 mm.
Response 13: Thank you to for the insightful corrections. You are completely correct that the original statement regarding "166.1 mm accounts for more than 70% of annual precipitation" has a mathematical contradiction with the range of "annual precipitation 600-1200 mm", due to an inaccurate data reference and we apologize for this confusion. We have thoroughly revised the text based on reliable data from the latest literature (He et al., 2024) to resolve this contradiction and improve our description. he relevant sentence now reads: “…, and the long-term annual precipitation ranges from 600 to 1200 mm, with precipitation mainly concentrated from June to September, which accounts for about 86% of the annual total, with a recent decadal average (2010–2020) of 705 mm (He et al., 2024).” We thank you again for your valuable suggestion, which has improved the accuracy of our manuscript.
References:
He, K., Hu, X., Wu, Z., Zhong, Y., Zhou, Y., Gong, X., & Luo, G. (2024). Preliminary analysis of the wildfire on March 15, 2024, and the following post-fire debris flows in Yajiang County, Sichuan, China. Landslides, 21(12), 3179-3189.Comment 14: 11. L474 There seems to be an error in Fig. 10d: the label for flow velocity and design frequency suggests P = 2%, but from the context it may be P = 1%. A similar issue appears in the title of Appendix B, where the panel (b) “Design frequency P = 1%” should likely be “P = 2%”. Please check all labels carefully.
Response 14: Thank you for your careful review and helpful suggestions. We have corrected the writing error by thoroughly checking and revising the labels in Figure 10 and the Appendix B to ensure consistency. Specifically: (1) the label for Fig. 10d has been updated to indicate flow velocity at the design frequency P = 2%; (2) the title of Appendix B has been changed to “(b) Design frequency P = 2%”. We appreciate your feedback, which has significantly improved the precision of our details.Comment 15: 12. L588 “logical functions” should be “logistic functions”.
Response 15: Thank you for your careful suggestion. Following your valuable suggestion, we have corrected this expression and changed the term to "logistic functions".Comment 16: 13. L592 The definition and calculation of R², MRE and other performance indices should be described in the Methods section rather than in the Discussion. Please consider moving the description to the methodological part for clarity.
Response 16: Thank you for your valuable suggestion. Following your advice, we have moved the definition and calculation of R², MRE and other performance indices to the Methods section. This adjustment significantly improves the clarity, and we thank you again for your insightful comment.
Finally, we deeply appreciate your valuable suggestion, which has significantly strengthened our manuscript. Thank you for investing your time and effort in providing feedback. We strive to provide detailed responses and careful revisions, and sincerely appreciate your constructive feedback and guidance, and we hope these improvements meet the journal’s standards for publication. Should further clarifications be needed, we are fully committed to addressing them promptly. Thank you again for your valuable suggestions and professional guidance.
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This manuscript is mainly focus on the buildings damaged by post-fire debris flows in mountain village. The authors have conducted detailed field investigations and reconstructions of disaster scenarios by numerical simulation, and development of physical vulnerability model for damaged buildings. The authors provide a comprehensive review of existing statistical models and indicators for vulnerability assessment, supplemented by extensive comparative analysis with previous research. Overall, this manuscript is interesting and it offers essential insights for assessing the impacts of post-fire debris flows on buildings and it’s helpful for mitigation strategies. Therefore, in my opinion, this manuscript is suitable for the scope of the journal, however, some suggestions are given for improving the manuscript.
Some comments on the manuscript: