Long-Term Subsidence Assessment by LiCSBAS and Emerging Hot Spot Analysis in Kathmandu Valley

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors Sagar Rawal and Guoquan Wang employ LiCSBAS for InSAR analysis using Sentinel-1 imagery to identify subsidence-vulnerable areas. This research is important for urban planners and policymakers concerned with groundwater management. However, I believe the manuscript requires major revisions before it can be considered for publication. My concerns are as follows:

• The novelty of this study is not clearly articulated. Please explicitly state the unique contributions of your research and how it advances the current understanding of subsidence analysis in stressed aquifers under urbanization.
• Abbreviations, such as EHA, must be defined upon their first use and used consistently throughout the manuscript, including in the discussion and conclusion sections.
  Introduction: The introduction is currently inadequate and lacks essential components. It should be rewritten to include:
  1. A clear statement of the main problem being addressed.
  2. A review of previous methodologies and datasets used in similar studies.
  3. Identification of the research gap.
  4. A description of your proposed approach to address this gap.
  5. A clear list of the study's aims.
• Please overlay the zonal analysis of subsidence for the selected ROI onto Figure 13b for better visualization and analysis.
• The methodology for generating the flood risk map is unclear. Please provide a detailed explanation of the data sources, controlling factors, and processing steps involved. Additionally, overlay the zonal analysis of subsidence for the selected ROI onto this map.
• The statement regarding the correlation between population density and subsidence in Section 3.6 contradicts the zonal affected area shown in Figure 7a. Please carefully review and correct the results in this section.
• The discussion section lacks depth and should be expanded to include comparisons with other published work in similar environments and with similar populations. Discuss the broader implications of your findings beyond the study area.

Best wishes

Comments on the Quality of English Language

The manuscript requires editing by a native English speaker to correct grammatical errors.

Author Response

We sincerely appreciate the valuable feedback provided by the you and extend our gratitude for their insightful suggestions. We have carefully addressed their comments and made the necessary revisions to the manuscript as following   Comments 1: [ The novelty of this study is not clearly articulated. Please explicitly state the unique contributions of your research and how it advances the current understanding of subsidence analysis in stressed aquifers under urbanization. Abbreviations, such as EHA, must be defined upon their first use and used consistently throughout the manuscript, including in the discussion and conclusion sections.
Introduction: The introduction is currently inadequate and lacks essential components. It should be rewritten to include:
1. A clear statement of the main problem being addressed.
2. A review of previous methodologies and datasets used in similar studies.
3. Identification of the research gap.
4. A description of your proposed approach to address this gap.
5. A clear list of the study's aims.]   Response 1:    We sincerely appreciate the valuable feedback provided by the reviewer and extend our gratitude for their insightful suggestions. we agree with your concerns of clear statement missing and also the introduction is not structured well. We took your full suggestion and hence fully revised our introduction section in following structure (Introduction > Past Literature Review > Summary of our proposed approaches > Our Main Objectives for this study ). We have briefly described the land subsidence and it’s impact in global scale. Then we described the present situation of groundwater problem and it’s impact on the land subsidence. Next we thoroughly described the all the literature review existed so far for quantifying subsidence of our study reason and next we pointed the research gap in these literature. After that we describe our methodology and short summary of what tools we will use and why this tool is beneficial in our research. Finally we describe our main objectives for to summarize our aim for this study.    Comments 2: [ Please overlay the zonal analysis of subsidence for the selected ROI onto Figure 13b for better visualization and analysis ] Response 2: We have overlayed our zonal analysis ROI to the Figure 13b as you have suggested for better visualization.    Comments 3: [ The methodology for generating the flood risk map is unclear. Please provide a detailed explanation of the data sources, controlling factors, and processing steps involved. Additionally, overlay the zonal analysis of subsidence for the selected ROI onto this map.]   Response 3:     Thank you for pointing our this. we didn’t realize we missed this part. We are very thankful for your review to bringing this up. [The author has used the dataset of (Elevation, Slope, Drainage density, Distance form river, TIW and curvature, Rainfall, Soil Texture, Land use and Geology ) to create a Flood susceptibility map. Additionally he used Population density, Road density , Literature Rate, Literate population density )  to create the Vulnerability map. He used AHP to calculate the weight of each factors and finally combined them both to create a risk map.] our response includes [Chadudhary using Analytical Hierarchy process created the flood risk map from by combining flood susceptibility and vulnerability map of KV. He used 14 different factors (eg Elevation, slope, Rainfall, Land use, curvature, Population, Literacy and more) as input parameters for AHP to calculate their weight. His flood risk map shows the northern and western part as high to very high-risk zone (Figure 15a).] you will find this in page no. 19 in first paragraph of sub-section flooding effects in line 3   Comments 4:   The statement regarding the correlation between population density and subsidence in Section 3.6 contradicts the zonal affected area shown in Figure 7a. Please carefully review and correct the results in this section. Response 4:    We clearly misinterpreted the details here. We discussed about this and come to conclusion that unlike subsidence map which is grid based, population is not distributed in grid like pattern. How large is the area, the residential building could be concentrated at some points locations. Also the area with major subsidence has many industries, commercial buildings, educational institute where people works but they don’t live in these places due to high rent and less rented apartment. Hence groundwater extraction is very high but population density is low in some of these areas. We have outlined these points in our revised paper thoroughly.    Comments 5:     The discussion section lacks depth and should be expanded to include comparisons with other published work in similar environments and with similar populations. Discuss the broader implications of your findings beyond the study area. Response 5:      We agree with your points. we have revised our discussion to briefly describe what is our findings and how close it aligns with already published works. We also describe what is new findings from our research work and how it can be helpful for developing countries like Nepal where urbanization is a growing problem and water management and subsidence mapping hasn’t been considered by policy maker until it’s too late to realize. We also added a figure for some in depth analysis of our research findings.    we hope, we are able to address your concerns. We again thank you for your time and your consideration to review our manuscript.   

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article addresses the important issue of the magnitude of land subsidence in relation to geology, groundwater level deposition and atmospheric conditions using modern techniques (LiCSBAS and Emerging Hot Spot Analysis) in the Kathmandu valley. After reading this article, the following comments arise:

1) What is the purpose and scope of the work ?

2) What is the novelty/originality of this material ?

3) The research results obtained in the study and their analysis are not objectionable, but the article is too long (overloaded with results) and there is a lot of information, I suggest dividing it into two separate parts, keeping the correct structure for this type of studies

4) Lack of discussion of the obtained results (chapter 4) understood as comparing and commenting own results obtained in this work with similar results obtained in the world on this type of soil.

5) Conclusions (chapter 5) should contain the most important results of the work and they should be related to the aim and scope of the work which should be defined at the beginning of the work (see note 1)

6) There is a lack of a broad and thorough literature review on the subject, the literature is mainly from the research object and there is no reference to other parts of the world with similar problems and phenomena, a revised literature review would greatly facilitate the discussion of the results obtained (see note 4)

7) In general, the article is too long with an incorrect structure that needs to be corrected in this respect, it currently needs a lot of additions

Comments on the Quality of English Language

see comments for Authors

Author Response

We sincerely appreciate your valuable feedback and constructive suggestions on our manuscript. Below, we provide detailed responses to your comments and explained necessary revisions made to our manuscript.

Comment 1: What is the purpose and scope of the work?

Response 1: The primary objective of this study is to examine long-term subsidence trends in Kathmandu Valley from 2017 to 2024 using LiCSBAS and InSAR time-series data. The scope extends to evaluating subsidence rates, identifying key influences such as groundwater extraction, population growth, and land use, and assessing the Melamchi Water Supply Project (MWSP) impact on these trends. Our goal is to offer valuable data-driven insights to support sustainable urban planning and groundwater management. To this end, we have completely revised the introduction section, clearly defining the aim and scope across the first two paragraphs of the updated manuscript.

Comment 2: What is the novelty/originality of this material?

Response 2: We are honored to highlight that this research pioneers the use of LiCSBAS-based InSAR processing combined with Emerging Hotspot Analysis (EHA) to explore long-term subsidence patterns in Kathmandu Valley. Unlike prior studies that focused on short-term monitoring, our work provides a detailed eight-year spatiotemporal analysis, revealing cumulative displacement trends. Moreover, we present the first empirical evidence of subsidence reduction linked to enhanced surface water supply from MWSP, validating governmental efforts. The innovative integration of EHA with InSAR data for statistical trend validation introduces a novel methodological framework, potentially applicable to regions worldwide facing similar groundwater-induced subsidence issues .In the fifth paragraph of the introduction section, we have highlighted the critical research gaps this study addresses, which previous research work have overlooked.

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Comment 3: The research results obtained in the study and their analysis are not objectionable, but the article is too long (overloaded with results) and there is a lot of information, I suggest dividing it into two separate parts, keeping the correct structure for this type of studies.

Response 3: We sincerely appreciate the reviewer’s thoughtful feedback. We acknowledge that subsidence in Kathmandu is shaped by diverse factors, compounded by the region’s complex geology, which has not been thoroughly explored in previous studies. This necessitated a detailed analysis of correlations with factors like groundwater extraction and land use, supported by numerous figures that unfortunately extended the text length. We hope the reviewer graciously understands the depth required for this pioneering work and accepts our efforts to refine the conclusion while maintaining scientific integrity.

If deemed necessary by the editorial team, we are open to dividing the study into two parts: one focusing on subsidence analysis using LiCSBAS and InSAR, and another dedicated to EHA-based pattern detection and mitigation strategies.

Comment 4: Lack of discussion of the obtained results (chapter 4) understood as comparing and commenting own results obtained in this work with similar results obtained in the world on this type of soil.

Response 4: We appreciate the reviewer’s insightful concern and have completely revised the Discussion section accordingly. We begin by explaining the significance of our findings for policymakers, researchers interested in tectonic motion, and environmentalists studying regional subsidence. We reviewed global literature on significant subsidence but noted the absence of Kathmandu in many studies, possibly due to limited published data or evidence, which our work now brings to attention. We also compared our results with research demonstrating hydro-connectivity between streams and aquifers, reinforcing our observations. Additionally, we explored subsidence in regions like Mexico and Jakarta, where rapid urbanization and over-extraction from unconsolidated aquifers mirror our findings. To enhance accessibility, we have developed an online web application for result visualization (https://ktmsub.alwaysdata.net. ). We trust these revisions address the reviewer’s concerns effectively.

Comment 5: Conclusions (chapter 5) should contain the most important results of the work and they should be related to the aim and scope of the work which should be defined at the beginning of the work (see note 1).

Response 5: We are grateful for this constructive suggestion and have also completely revised the Conclusion to align with the study’s aim and scope. The updated section summarizes the methodologies employed and highlights key results, including subsidence rates up to 21 cm/year and the first evidence of changing patterns following MWSP completion, as anticipated by prior literature. We also draw comparisons with global regions facing similar challenges, ensuring relevance to our objectives. We hope this revision meets the reviewer’s expectations.

Comment 6: There is a lack of a broad and thorough literature review on the subject, the literature is mainly from the research object and there is no reference to other parts of the world with similar problems and phenomena, a revised literature review would greatly facilitate the discussion of the results obtained (see note 4).

Response 6: We extend our heartfelt thanks to the reviewer for this valuable input. We acknowledge the initial lack of a structured introduction and limited global context. Accordingly, we have restructured the introduction into sections: an overview of land subsidence and its global impact, a discussion of groundwater issues and their influence on subsidence, a comprehensive review of existing literature on Kathmandu’s subsidence with identified research gaps, a summary of our proposed methodology and tool benefits, and a clear statement of our objectives. This revision aims to enrich the discussion of our findings.

Comment 7: In general, the article is too long with an incorrect structure that needs to be corrected in this respect, it currently needs a lot of additions.

Response 7: We have thoughtfully revised the introduction to include a concise review of global subsidence processes and existing research, followed by a clear outline of our aims. The discussion and conclusion sections have been refined for brevity and clarity while retaining essential findings. We are confident these enhancements address the structural concerns and hope they satisfy the reviewer’s expectations.

Additionally, We also have revised the title of our study from "Long-Term Subsidence Assessment by LiCSBAS and Emerging Hot Spot Analysis in Kathmandu" to "Long-Term Subsidence Assessment by LiCSBAS and Emerging Hot Spot Analysis in Kathmandu Valley." This change ensures clarity, as readers might otherwise assume the research focuses solely on the Kathmandu district rather than the broader watershed encompassing three districts that form the valley. The addition of "Valley" addresses this potential misinterpretation. Furthermore, following the required revisions, we have updated our abstract to maintain precision while clearly outlining essential details about the study area, the significance of the research, the methodologies employed, and the key results obtained.

 

We deeply value the reviewer’s insightful comments, which have significantly strengthened our manuscript’s clarity and impact. We kindly request reconsideration of this revised submission and welcome further guidance. Thank you for your time and consideration.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I found useful and interesting the manuscript land-3521193 submitted by Rawal S. and Wang G. The authors considered the significant pressure on the aquifer system of Kathmandu Valley, resulting in pronounced land subsidence. The investigation utilized LiCSBAS for InSAR analysis (Sentinel-1 imagery from 2017 to 2024) to describe areas affected by land subsidence. The results indicate a peak subsidence rate of 21 cm annually, culminating with an overall subsidence of around 1.6 meters. The most significant subsidence rates have been recorded in the northwestern area, especially in Maharajgunj, Samakhusi, and Manamaiju, where there is a high concentration of population density and extensive industrial and commercial activities. Subsidence has extended into the peripheries and open regions in the eastern and southern areas of Lalitpur and Bhaktapur districts. A spatiotemporal analysis was performed through Emerging Hotspot Analysis utilising InSAR datasets. The interesting application of EHA indicate a slowdown in the intensity of subsidence in high-risk regions, suggesting changes in deformation patterns. The most relevant regions experiencing subsidence are situated above the Kalimati and Gokarna Formations, characterised by fine-grained, compressible sediments. Soil compaction, excessive groundwater extraction, and rapid urban expansion in natural recharge zones are the primary factors contributing to subsidence. The paperi s well organized and I think conclusions are reasonable and well founded. Anyway I suggest to include the studied area in a wider and more global context, as shown (as an example) in Herrera García, P. Ezquerro, R. Tomás, M. BéjarPizarro, J. LópezVinielles, M. Rossi, R.M. Mateos, D. Carreón-Freyre, J. Lambert, P. Teatini (2021) Mapping the global threat of land subsidence. Science, 371, 34-36. The authors utilized water level to explain the observed phenomena. Groundwater residence time (proportional to the age of groundwaters) could be more effective if available in the scientific literature as proposed (as an example) by G. Martinelli, A. Chahoud, A. Dadomo, and A. Fava (2014) Isotopic features of Emilia-Romagna region (North Italy) groundwaters: environmental and climatological implications. J.Hydrol., 519, 1928-1938. The excess of groundwater withdrawal is the believably most relevant driver of phenomena observed by the authors. I hope the paper will be soon accepted and published after some possible minor updates.

 

 

Author Response

We extend our heartfelt gratitude for your invaluable feedback and thoughtful suggestions, which have greatly enhanced the quality of our manuscript.   We have thoroughly revised the introduction section, incorporating a review of numerous papers to highlight Kathmandu’s global ranking in population density and to identify other regions experiencing significant subsidence under similar environmental conditions. We then drew a careful comparison, noting that cities such as those suffering from overexploitation of groundwater, rapid urbanization, and unconsolidated sediment-rich aquifers face substantial subsidence increases trends that may similarly intensify in our study area given the rising rates of urbanization and groundwater extraction each year.   We have also refined the discussion section to elucidate our results and reinforce the finding that deep aquifers are the primary contributors to subsidence. To support this, we reviewed literature providing evidence of water connectivity between shallow aquifers and nearby streams, which replenishes extracted water and causes only temporary compression insufficient to account for the long-term subsidence observed in our data. Recognizing the limited research on deep aquifers, we gratefully adopted the paper by G. Martinelli, as recommended by you, to contextualize our findings. Specifically, we integrated the following text into the third paragraph of the Discussion section, on the eighth line from the end:   "[While research on the recharge mechanisms of deep aquifers in our study area remains limited, Martinelli’s study in Emilia-Romagna, Italy, identified land subsidence resulting from the overexploitation of deep aquifers through isotopic analysis.]"   Furthermore, we have amended the title from "Long-Term Subsidence Assessment by LiCSBAS and Emerging Hot Spot Analysis in Kathmandu" to "Long-Term Subsidence Assessment by LiCSBAS and Emerging Hot Spot Analysis in Kathmandu Valley." This adjustment ensures clarity, preventing the misinterpretation that the research is confined to the Kathmandu district alone, rather than encompassing the watershed of three districts forming the valley. To complement this, we have revised the abstract to maintain precision, succinctly presenting essential details about the study area, its significance, the methodologies applied, and the key results achieved.   We are deeply appreciative of your insightful comments, which have significantly improved the clarity and impact of our manuscript. We humbly request reconsideration of this revised submission and warmly welcome any further guidance you may offer. Thank you sincerely for your time and consideration.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The authors have successfully addressed all of my concerns. I recommend the manuscript for acceptance in its current form.

Sincerely

Reviewer 2 Report

Comments and Suggestions for Authors

At this moment I suggest to publish this material in Land journal