Digital Geospatial Twinning for Revaluation of a Waterfront Urban Park Design (Case Study: Burgas City, Bulgaria)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study applies digital geospatial twinning technology to the redesign of urban waterfront parks, developing models and scenario simulations to support low-carbon and climate-resilient strategies. The case study offers valuable practical and academic insights for sustainable waterfront renewal.

However, a few areas need further refinement:

1） The carbon sink formula (page 11) directly adopts international parameters (like MAI and BCEF) without verifying their suitability for coastal vegetation. It would be helpful to add localized calibration data—for example, actual biomass measurements from sampled trees.

2） Comparisons between scenarios lack quantitative data or clear metrics. Also, the long-term benefits of Scenario 2 need clarification—what time frame was used for those calculations?

3） The design doesn’t sufficiently address climate adaptation for risks like sea-level rise or storm surges.

4） Carbon sink calculations should factor in real-world variables like vegetation survival rates and maintenance costs.

5） Since the case site is near an airport, discuss how airspace restrictions or geological risks might affect the design. Could these constraints limit the broader applicability of the approach?

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted file. All revisions in the article are marked in blue.
Point-by-point response to Comments and Suggestions for Authors
Comments 1: The carbon sink formula (page 11) directly adopts international parameters (like MAI and BCEF) without verifying their suitability for coastal vegetation. It would be helpful to add localized calibration data—for example, actual biomass measurements from sampled trees.
Response 1: Thank you for your comment. This study considers that the urban park project is funded by the municipal budget. Therefore, the analytical material supporting the discussed scenarios for the coastline must adhere to the methodological requirements established by the Bulgarian Ministry of Environment and Water, as referenced in source 38. These guidelines were developed by specialists who evaluated the applicability of international parameters to Bulgarian conditions, particularly regarding the parameter "The annual change of carbon stock in biomass." Additionally, the ministry provides specialized guidelines for the species used in urban greening, taking into account the impact of climate change on the country's geographical conditions. We appreciate your input and will consider it in our ongoing research in the southern Black Sea coastal area.
Comments 2: Carbon sink calculations should factor in real-world variables like vegetation survival rates and maintenance costs.
Response 2: Thank you for the comment, the above response 1 also applies to this issue.   Comments 3: Comparisons between scenarios lack quantitative data or clear metrics. Also, the long-term benefits of Scenario 2 need clarification—what time frame was used for those calculations?   Comments 4: The design doesn’t sufficiently address climate adaptation for risks like sea-level rise or storm surges.     Comments 5: Since the case site is near an airport, discuss how airspace restrictions or geological risks might affect the design. Could these constraints limit the broader applicability of the approach?

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

When discussing the potential of urban forests as nature-based solutions (lines 84–85), discuss how contextual sensitivity and requirements, mentioned as a series of challenges, may be addressed.

Expand upon the usage of digital twins beyond the field of spatial urban planning: how can this model and methodological approach be used for other, varied disciplines and requirements?

As “continuous synchronization” is needed for obtaining a precise depiction of the physical environment, address the synchronization intervals and their implications (in terms of cost-effectiveness, time, and manpower), as well as potential challenges for reviewing and implementing plans with obsolete data (digital twins that have not been updated).

Hypothesize and engage in a speculative scenario when the obtained data and spatial recommendations differ significantly from the previously adopted development plans. E.g., if there is a notable discrepancy between the obtained data from the digital twin and the General Development Plan for Residential Construction. What is the hypothesized course of action in this instance? Supposing that the digital twins were developed after the spatial legislation adoption and implementation.

Increase the quality of Figures 2, 3, 11, 12, 13, 14, and 15. They are currently pixelated and barely legible.

Discuss the necessity or lack thereof of preparatory work for digital twin implementation in various times of the year (summer/winter) for more precise data imaging, as tree canopies were mentioned as one of the challenges in data imaging.

As some image limitations were mitigated through manual editing, manual segmentation, and noise filtering, what was the overall adopted margin for error, and how can potential deviation from said margin influence the dataset’s accuracy?

As co-creation was highlighted as a key principle, expand upon the input obtained from key professions, educational and scientific institutions, administrative bodies, local communities, non-governmental organizations, and businesses, highlighted in (lines 430–431). What was the number of representees from each category? Could the results skew in favor of a certain solution, and how was that variable corrected?

Expand upon the specialty of the team of experts from various fields (line 440).

How was the decision process for “choosing the proposals for the development of the project area predefined as a drop-down list” (lines 444–445) implemented? By whom?

Expand upon “Other” proposals highlighted in Table 2, as they provide the highest count of examinees.

When appointing the designation for “distinguished zones of degraded vegetation,” were applicable professionals (e.g., forestry engineers) consulted before making said designation?

Was underground parking (garage) considered to address the identified shortage of parking spaces in the neighborhood?

As coastal improvement was the primary focus of this study, was a larger-scale intervention in the built environment considered, e.g., extending coastal vegetation as green corridors into the street matrices or other architectural and urban-scale interventions?

Expand the discussion section with a speculative scenario – if the suggestion based on the digital twin and presented findings were to be implemented in situ – how would one monitor the results and their impact on a wider urban area, as well as the intervals of check-up and potential new digital twins to be generated, to further enhance the development of the area in question?

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attachment and the corresponding revisions/corrections highlighted/in track changes in the re-submitted file.

All revisions in the article are marked in blue. 

Point-by-point response to Comments and Suggestions for Authors

Comments 1:     When discussing the potential of urban forests as nature-based solutions (lines 84–85), discuss how contextual sensitivity and requirements, mentioned as a series of challenges, may be addressed.

Response 1: Thank you for your recommendation. The text has been expanded in lines 87-97

Comments 2: Expand upon the usage of digital twins beyond the field of spatial urban planning: how can this model and methodological approach be used for other, varied disciplines and requirements?

Response 2: Thank you for your suggestion. We expand the section upon digital twin usage beyond spatial urban planning by adding a concise paragraph that demonstrates the methodology's broader applications (Lines 111-131).   Comments 3: As “continuous synchronization” is needed for obtaining a precise depiction of the physical environment, address the synchronization intervals and their implications (in terms of cost-effectiveness, time, and manpower), as well as potential challenges for reviewing and implementing plans with obsolete data (digital twins that have not been updated).   Comments 4: Increase the quality of Figures 2, 3, 11, 12, 13, 14, and 15. They are currently pixelated and barely legible.   Comments 5: As some image limitations were mitigated through manual editing, manual segmentation, and noise filtering, what was the overall adopted margin for error, and how can potential deviation from said margin influence the dataset’s accuracy?

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors and Editors,

Study focuses on developing a digital geospatial twin for the unique coastal conditions in Bulgaria. The objective is to create an up-to-date 3D model that merges diverse geospatial data into a single accurate representation of the waterfront area. Using this twin, the study evaluates three design scenarios for revitalising the coastal park in collaboration with local stakeholders.

Authors propose the digital twin as a planning tool to assess site conditions, incl. carbon sequestration under different scenarios, and to inform about alternatives. Stakeholder engagement was demonstrated through participatory workshops to involve residents and professionals in co-designing the park improvements.

In general, this study tends to contribute to urban planning and geospatial analysis. It demonstrates the power of digital geospatial twins to bridge accurate/high-quality data and alternative solutions, converting detailed spatial measurements into actionable design insights. At the same time, it addresses practical challenges, including technical complexity and stakeholder processes, that need to be managed on the path toward climate-adaptive urban areas/cities. The Burgas case is an innovative example relevant to researchers and practitioners interested in digital twins, sustainable urban design, and collaborative geospatial decision-making.

However, based on the proposed study and its outcome, the reviewer admits that the current digital twin does not incorporate specific urban systems, e.g. traffic flows and socio-economic data, and it omits future climate simulations despite the site’s known climate vulnerabilities. The authors propose maintaining a city-wide digital twin (with periodic updates by municipal authorities) to spread costs (equipment, computing, expertise) and benefits (updated 3D model), but sustaining such an initiative over time remains challenging. Expanding the twin to include these aspects would enhance its utility as a comprehensive planning tool for long-term resilience.

The reader/reviewer of the paper would be required to identify the evidence about how the provision of up-to-date data and testing their application deserves publication in a scientific journal (see study aim in lines 120-123).

The quality of the manuscript should be improved. Thus, it is advised to consider the following:

1. The readability of figures (at least 2, 3, 15, 16) must be improved.
2. What exactly are the values assumed in the development scenarios in the forest area, as indicated in line 397, sub-section 2.3?
3. Why do the authors see the importance of converting to grassland in the study, as indicated in lines 419-420, at the end of sub-section 2.3?
4. As there is no reference to the REVALUE project and other sources, the reader cannot learn about the profile of those 30 experts mentioned in line 441, sub-section 2.4.
5. The meaning of Table 2, in general, and “No data” in the first row, specifically, to the study is unclear. Please, explain or skip it.
6. The relation of accessible routes (Fig.14) and the patterns of functional zoning (Fig.15) to the proposed scenarios is not clear: (1) routes are relevant also to scenarios 0 and 1, (2) what grounds the functional zoning, e.g. local or regional, or national governmental provisions/regulations/classifications? Please provide a reference.
7. The essence of cadastral maps is real property/land units’ borders, which cannot be read from Fig.16. Moreover, what is the meaning of its modification in the paper? Please provide a reference.
8. The Conclusions (section 5) are provided in a too general manner. There are no references to the provided scenarios and the outcome of data testing in the study. What do the authors mean by “adequate basis” and effectiveness of planning and management (see line 790) if the socio-economic and cost assessments are not the research subject in the paper?
9. The authors present only some technological possibilities and tools, which is fine, however, how the applied possibilities “are a natural solution” (see lines 797-798)?

Given all those mentioned above, I recommend that the editors address MAJOR REVISION before accepting the manuscript for publishing, as it has serious flaws that must be avoided.

Wishing you the best of luck with your further research.

With best regards

The reviewer

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted file.

All revisions in the article are marked in blue.

Point-by-point response to Comments and Suggestions for Authors

Comments 1: The reader/reviewer of the paper would be required to identify the evidence about how the provision of up-to-date data and testing their application deserves publication in a scientific journal (see study aim in lines 120-123)

Response 1: Thank you for your recommendation. Edits have been made to the Results section to support the research objective and present clearer results for the tasks set.

Comments 2: The readability of figures (at least 2, 3, 15, 16) must be improved.

Response 2: Thank you for the recommendations. The figures are replaced.   Comments 3: However, based on the proposed study and its outcome, the reviewer admits that the current digital twin does not incorporate specific urban systems, e.g. traffic flows and socio-economic data, and it omits future climate simulations despite the site’s known climate vulnerabilities. The authors propose maintaining a city-wide digital twin (with periodic updates by municipal authorities) to spread costs (equipment, computing, expertise) and benefits (updated 3D model), but sustaining such an initiative over time remains challenging. Expanding the twin to include these aspects would enhance its utility as a comprehensive planning tool for long-term resilience. Response 3: Thank you for your comment. Our views on the challenges you raise are shared in the discussion section, but in light of your comment, we have partially expanded the text with explanations – lines 781-788. We acknowledge that our current digital twin, while focused on park-level geospatial and ecological data, does not yet integrate urban systems like traffic or socio-economic data, nor future climate simulations. We agree that incorporating these elements is vital for a comprehensive planning tool for long-term resilience, and while sustaining a city-wide twin presents challenges, our proposed collaborative model aims to share costs and maximize the benefits of continuous updates.   Comments 4: What exactly are the values assumed in the development scenarios in the forest area, as indicated in line 397, sub-section 2.3? Comments 6: As there is no reference to the REVALUE project and other sources, the reader cannot learn about the profile of those 30 experts mentioned in line 441, sub-section 2.4. Response 6:Thank you for your comment. The experts’ profiles are added in lines 493-497.   Comments 7: The meaning of Table 2, in general, and “No data” in the first row, specifically, to the study is unclear. Please, explain or skip it. Response 7:Thank you for the comment. We are changing the designation for greater clarity.   Comments 8: The relation of accessible routes (Fig.14) and the patterns of functional zoning (Fig.15) to the proposed scenarios is not clear: (1) routes are relevant also to scenarios 0 and 1, (2) what grounds the functional zoning, e.g. local or regional, or national governmental provisions/regulations/classifications? Please provide a reference. Response 8: Thank you for the suggestion. The text has been edited and expanded - lines 697-705   Comments 9: The essence of cadastral maps is real property/land units’ borders, which cannot be read from Fig.16. Moreover, what is the meaning of its modification in the paper? Please provide a reference. Response 9: https://kais.cadastre.bg/bg/Map Thank you for your comment. During the most recent verification at the Geodesy, Cartography and Cadastre Agency, the changes have already been implemented, and the area in question now falls outside the scope of the coastal park — part of it has been designated as a land plot for transport, while another portion has been integrated into the beach strip. In view of this, we would prefer that the „Ongoing procedure for modification of the cadastral map” be removed from the paper.   Comments 10: The Conclusions (section 5) are provided in a too general manner. There are no references to the provided scenarios and the outcome of data testing in the study. What do the authors mean by “adequate basis” and effectiveness of planning and management (see line 790) if the socio-economic and cost assessments are not the research subject in the paper? Response 10: Thank you for your critical comment. The edits are reflected in lines 896-904.   Comments 11: The authors present only some technological possibilities and tools, which is fine, however, how the applied possibilities “are a natural solution” (see lines 797-798)? Response 11:Thank you for the comment. It is a natural solution because the data and information based approach in planning is becoming the leading one.we have added additional text explaining why we believe that this is a “natural” solution

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Authors' prompt responses and manuscript amendments are appreciated.

The implemented alterations have significantly improved the clarity for presented research datasets, and the paper is now considered ready for publication. 

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Editors and Authors,

The manuscript has been improved, addressing the reviewer's comments. So, it is good enough to be published in the journal.

Best wishes,

The Reviewer