First and foremost, I wish to extend my heartfelt gratitude to the authors and editors for affording me the distinct privilege of reviewing this document. The opportunity to delve into such a subject matter, which is not only of paramount importance but also of personal interest to me, has been exceedingly rewarding. The document's thematic relevance coupled with its scholarly rigor is commendable, and I have found the experience to be exceptionally enlightening.

Upon a comprehensive examination of the manuscript, I have found it to be meticulously written, demonstrating a high degree of linguistic proficiency and a clear, logical flow of ideas. The overall organization of the content is commendable, facilitating an intuitive understanding of complex concepts and findings related to sea-level rise. However, despite the document's many strengths, I have identified a few structural areas that could benefit from further refinement. These include the integration of additional sub-sections for enhanced clarity, reorganization of certain sections to improve the narrative flow, and the inclusion of more detailed discussions in areas where the current exposition appears somewhat cursory.

The literature review undertaken in this study is particularly noteworthy. The authors have embarked on a formidable task, sifting through an extensive body of research to distill essential insights and findings relevant to the discourse on sea-level rise. This effort is laudable, and I wish to extend my special congratulations to the team for their diligence and scholarly rigor. As an expert in the field, I could enumerate numerous articles and reports that are absent from the bibliography. Nonetheless, I recognize the inherent challenges in curating a comprehensive yet pertinent bibliography. The objective is not to amass an exhaustive list of all conceivable literature but to judiciously select works that are foundational and directly relevant to the study's aims. In this respect, I am persuaded that the authors have exercised sound judgment, ensuring that the included references significantly contribute to the advancement of the discourse.

In closing, I would like to reiterate my appreciation for the opportunity to engage with this scholarly work. The insights gained from this review will undoubtedly contribute to my own understanding and research in the field of sea-level rise. I look forward to seeing the final version of this document published and to possibly contributing further to this vital area of study in the future.

I am confident that this document will prove immensely beneficial to the scientific community and serve as a valuable guide for policy-making decisions in anticipation of the imminent arrival of Sea Level Rise (SLR). My proposal includes minimal conceptual changes, in addition to some formal adjustments, which I will detail below:

1. Structural Enhancements: I find the absence of a dedicated conclusions section, or a "summary for policymakers," to be a notable omission. While the abstract performs a similar function, a robust set of general ideas articulated in a few paragraphs would greatly assist the sometimes cursory reading by those outside the scientific community, such as public officials, journalists, etc. This addition could significantly enhance the document's accessibility and utility by distilling its key insights into actionable guidance.

2. Development of Predictive Tools: The manuscript mentions the development of tools to forecast the scope and impacts of sea-level rise, yet this critical element seems to warrant further elaboration. The volume of scientific work on this topic, particularly regarding flooding, is remarkable. While it is not necessary to cite numerous studies, it is important to acknowledge that a significant portion of scientific efforts has focused on this issue for decades. This topic is likely one of the most published within the context of SLR.

3. Cartographic Techniques: Following the previous comment, exploring cartographic techniques that can simply represent the implications of sea-level rise holds tremendous communicative potential for raising risk awareness. This potential tool for awareness is not mentioned in the report but could be one of the most powerful means of communication.

4. Compliance with Coastal Laws: There is a minor oversight, easily rectified by a simple sentence, regarding the compliance with coastal laws by states. This issue has often been overlooked in most scientific works on SLR, yet it is a critical aspect of addressing and mitigating the impacts of sea-level rise.

5. Formal Consideration of References: Lastly, on a minor formal note, the references to Spanish agencies should be reviewed. Typically, such references have been published by the Ministry of Environment or similar bodies, whereas the text currently attributes authorship to the title of the work itself. This should be revised in accordance with the editorial policies.

In conclusion, while I applaud the document's current contributions to the field of sea-level rise research, these proposed enhancements could further increase its value and impact. By addressing these suggestions, the document could more effectively communicate its findings and recommendations to a broader audience, including policymakers, researchers, and the general public, thereby fostering a more informed and proactive approach to managing the challenges of sea-level rise.

Sea level Rise in Europe: Adaptation Measures and Decision Making Principles

Thank you for inviting me to review this paper. I think that assessing coastal adaptation across Europe is quite a challenging topic as it is very diverse. This is a solid review but I think it can be improved -- for example being clearer on what is happening versus what might happen in the future. I have made a series of comments to encourage reflection and improvement. I would see the response as requiring more than minor and hence they are major revisions -- there are a number of points to think about and consider. Below are some numbered major points and then some more specific remarks by line number.

1. It is important to distinguish between what is happening today (practise) and aspirations for the future (theory). For example, in Section 2.2.3 it is unclear how much these approaches are used today versus this is a recommendation for the future.
2. What are the strengths and limits of the literature review? One weakness is that adaptation measures are poorly reported in peer-reviewed literature so how representative is the sample? For example, could the review be enhanced by considering the grey literature?
3. On line 117 you say: ‘Although the literature examines in depth each type of response to sea level rise, accommodation measures are the most widely identified, followed by protection measures, advance measures, and finally retreat measures.’ What metric is used to come to this judgement? Based on my experience, I think the dominant adaptation to date has been upgraded coastal defences, reflecting that Europe has a large legacy of coastal defences. Sea-level rise has been considered in defence upgrades around the southern North Sea for 20 to 30 years – that is a lot of activity and investment in the Netherlands, Germany, Belgium and the UK, but it is not written about at the scale of each scheme? The author’s comments on this perspective is welcome if they have a counter argument.
4. Is there public supplemental data on the literature review analysis? It would be useful to have the identified source and the analysis as a legacy to support future scholarship in this topic.
5. Are the adaptation categories used unambiguous and are there any grey areas between them?
6. I have already mentioned the large legacy of protection in Europe and especially around the North Sea. The paper tends to talk at times like we have a blank slate when there are thousands of kilometres of dikes and millions of people who depend on them to live as they do today. Negative aspects of dikes are raised, but as they already exist these are tempered somewhat. The main question is how they will be raised/upgraded in the future and where a more radical change might be necessary? Of course, new dikes may be built in some locations – I do not have a feel for how large this need might be and welcome the authors insights about the relatively importance of both.
7. Box 1 – this is not referenced in the main text and the content is significant in size – I am unclear of the goal of this box? Also how useful is this box as Venice is a rather special case compared to Europe’s coast?
8. Section 3 Summary: key developments per basin – a key section –would be good to further develop specific Europe and European region recommendations.
9. The English could be tightened in general.

Some more detailed comments are as follows:

• Line 51 to 52 ‘. Traditional engineering solutions, here referred to as grey options, have dominated thinking and practice in coastal protection for several decades (Sancho, 2023).’ – I would say they have dominated for centuries – not to say there were not failures – but the defences were always rebuilt more strongly. For example see Kraus (1996) for many national portraits, or for a good national example -- the Netherlands (Van Koningsveld et al., 2008).
• Line 99 Are ‘early warning systems’ just an accommodation response? They work for the entire coastline and are fundamental to mobile protection defences like the Thames Barrier and MOSE barrier in Venice. I would argue that they are an example of ‘information measures’ that are becoming progressively more powerful and useful and support all adaptation measures to varying degrees.
• Line 104 to 106 – under retreat where does managed realignment for habitat creation sit – a common action over the last 20 years. It appears later, but suggest it is worthy of definition here.
• Line 123 Table 1 – seems like the SROCC report is quite an influential source here – suggests this is a rather high level analysis rather than looking at practise in Europe.
• Line 123 Table 1 -- 14 ‘Rising and advancing coastal land’ – I would say ‘Raising and advancing coastal land’.
• Line 123 Table 1 -- 14 ‘Rising and advancing coastal land’ – what insights do global analyses such as Sengupta et al (2023) provide on Europe?
• Line 123 Table 1 – 15 Beach and shoreface nourishment – is this really an advance strategy? If you introduce enough sand or gravel – yes? And maybe we advance in some areas because of an historical legacy of building in hazardous places. But sand and gravel are scarce and expensive so in general I think the goal is to hold the line. So I think this option is more nuanced than presented.
• Line 123 Table 1 – 16 Planned relocation – where is coastal restoration?
• Line 161 – what about avoiding salinisation of groundwater – that is of concern with sea-level rise especially when combined with overuse of these resources.
• Line 181 – restricting development can be considered a form of retreat – e.g., building setbacks along eroding cliffs?
• Line 220 to 223 – is this only accommodation? This information is useful for all coastal adaptation – it provides information on how high to build defences or how far to retreat.
• Line 240 to 242 – people behind defences can be evacuated when the early warning system suggests an event that might cause a defence failure – these types of responses are not well documented but happen in practise.
• Line 258 ' On the other hand, perceived intractability of climate change hinders the desire to adopt low-carbon behaviours (Xiang et al., 2019).’ – true but is it relevant here – this is climate mitigation and the section is about climate hazard risks. I would delete as a distraction or if important move to another more relevant section on synergies with mitigation.
• Line 263-264 – what ‘technical limits’ to protection – If you give an engineer enough resources, modern engineering will be able to provide a defence. The limits line much more in cost and cost-benefit, finance and social acceptance and also if sea-level rise is rapid (ice sheet collapse) – areas where there is much less research. This has been stated by Hinkel et al (2018).
• As an example to defend this view – the Thames Estuary Project planned defences of London against rises up to 5 m of sea-level rise (Tarrant and Sayers, 2012; Ranger et al., 2013).
• Line 291 -- Restoration and management of coastal ecosystems are more widespread than listed with good examples in UK and Germany. Also how much are these strategies adaptation and how much are they coastal restoration which is complementary but not necessarily adaptation?
• Line 320 – considering coastal and shoreface nourishment as an example of Advance seems incorrect – if enough sediment is used it might be the case. However, as erosion is the overwhelming trigger of this strategy and advance is short-term at best and most of these projects aspire to stabilise the shoreline rather than advance. Later you state nourishment is not sustainable contradicting earlier remarks.
• The national scale nourishment of the Netherlands where erosion is outlawed is not mentioned.
• Line 342 – references to support this statement?
• Line 364 – what is the difference between managed relocation and managed realignment – seem to be rather similar terms to me.
• Managed relocation and retreat seems to be something that is going to happen while earlier sections of discussed active projects – this is an important distinction is not made explicit.
• Page 15 “divided into 4 arrows” – don’t understand?
• Page 17 “Venice constantly raised the building construction levels, to cope with SLR” – this should refer to relative SLR as subsidence is the main historic driver.
• Line 386-387 – as much of this protection is in place I am not sure this is conveying the present choices.
• Line 467-469 – these SLR scenarios for the Wadden Sea seem rather precise – are the uncertainties being conveyed? – see line 557-559.
• Line 610-612 – what was the response to Xynthia in France – was there any retreat?
• Line 677-689 – the Thames Estuary 2100 project provides a real-world example of considering high-end SLR scenarios (e.g., Ranger et al., 2013) and might be used here.

References

Hinkel, J., Aerts, J.C.J.H., Brown, S. et al. 2018. The ability of societies to adapt to twenty-first-century sea-level rise. Nature Clim Change 8, 570–578, https://doi.org/10.1038/s41558-018-0176-z

Kraus, N.C. ed., 1996, June. History and heritage of coastal engineering. American Society of Civil Engineers, New York.

Ranger, N., Reeder, T. and Lowe, J., 2013. Addressing ‘deep’ uncertainty over long-term climate in major infrastructure projects: four innovations of the Thames Estuary 2100 Project. EURO Journal on Decision Processes, 1(3-4), pp.233-262.

Sengupta, D., Choi, Y.R., Tian, B., Brown, S., Meadows, M., Hackney, C.R., Banerjee, A., Li, Y., Chen, R. and Zhou, Y., 2023. Mapping 21st century global coastal land reclamation. Earth's Future, 11(2), p.e2022EF002927.

Tarrant, O. and Sayers, P.B., 2012. Managing flood risk in the Thames Estuary–the development of a long-term robust and flexible strategy. In Flood risk: planning, design and management of flood defence infrastructure (pp. 303-326). ICE publishing.

Van Koningsveld, M., Mulder, J.P., Stive, M.J., Van Der Valk, L. and Van Der Weck, A.W., 2008. Living with sea-level rise and climate change: a case study of the Netherlands. Journal of Coastal Research, 24(2), pp.367-379