The presented `Brief communication` manuscript documents a collaborative effort by a large group of multidisciplinary researchers. The aim of the project was to identify key topics in the fields of climate change and water resources, relevant to the Berlin-Brandenburg region (NE Germany). The paper briefly describes the study area, articulates the need for in-depth research and an actionable mitigation plan, outlines the methodology of the questionnaire, and presents the outcome – a list of proposed scientific questions to be addressed in the coming decade.

I have an overall positive impression of the manuscript. I would like to offer two general suggestions.

1. The title of the paper suggests a focus on “climate and water challenges”, yet among the identified 10 questions, there seems to be a bias towards water availability problems. For example, the selected questions in Category 1 and Category 2 are quite specific with respect to water balance of the Spree and Lausitz, while climate-related questions are quite high-level and are applicable almost universally. The same is seen in the Appendix TableS1, where the Water Management category clearly dominates. This, in my opinion, warrants some reflection. Does it have to do with the expertise of the survey participants and their Berlin residence?
2. It would be valuable to highlight the transferability of this collaborative and inclusive approach to a broader scientific network and other regions. There must be a reason why the authors present these pressing issues for BBR in the international journal, rather than simply passing them to the local authorities or publishing a white paper. Was there anything original about the methodology worth highlighting? What pitfalls did you identify during the survey? The authors touched on this in the final paragraph of the conclusions, but the message could have been delivered in a more structured way.

My minor suggestions (line-by-line):

Line 13: please add a reference to the D.Hilbert paper.

Line 17-18: use ‘mean annual’ instead of just mean

Line 27: please be more specific, e.g., “carbon dioxide emission reduction"

Line 29: the reference to “the Spree” lacks context. Please clarify that it refers to a river that a densely-populated urban center relies on for water supply, navigation etc. (i.e., what is written later in Lines 32-33)

Line 44: please be more specific, e.g., groundwater storage or quality decline.

Line 48: consider re-phrasing this sentence for clarity.

Line 55: I believe, the referenced paper is from 2011, not 2019. Please also check and cite more recent summaries (like GERICS). Some modelled scenarios project steady or increasing precipitation in Eastern Germany, including summer precipitation.

Line 82: please rephrase for clarity - the top 10 questions selected based on the questionnaire responses were compiled into a list, presented in Table 1

Line 83-84: this reads like a repetition of the information from the Introduction. Can be safely removed. There is no need for brackets in (BBR).

Line 118: Concluding remarks or Conclusions

Line 123 this sentence appears to be out of context: “Drought has been a topic on the research agenda at BBR for a long time”. Or does it belong to the next paragraph?

Line 125 – it is not totally clear what recommendation the authors are referring to.

General comments:

This article addresses the highly relevant subject of identifying key research questions on water and climate change in the Berlin-Brandenburg region. The format of a 'Brief Communication' is well suited to providing ideas and stimulating discussion, and aligns with the journal's requirements.

The article makes a valuable contribution by systematically identifying and prioritising research questions through a transparent, participatory process. The involvement of a broad spectrum of scientists demonstrates a clear commitment to transdisciplinary collaboration. The iterative co-design approach and multi-phase structure in particular indicate a thoughtful and inclusive methodology. It is especially commendable that the authors actively engage in public discourse and leave the confines of the academic “ivory tower” by formulating research questions that are meant to resonate beyond disciplinary boundaries. The publication also has the potential to raise awareness of regional water and climate challenges beyond the academic sphere. As such, it provides a solid basis for future research activities within the scientific community.

However, despite this potential, the article also reveals certain weaknesses. Most notably, it lacks sufficient reference to existing political strategies and to the ongoing research landscape in the region.

Specific comments

1. Lack of political and administrative context

The article fails to provide a context for the identified questions within the framework of existing political and administrative developments. Yet numerous strategic water management documents and ongoing processes already exist for the Berlin-Brandenburg region – just to name a few of them.

• Positionspapier Wasser Brandenburg (2022): https://mleuv.brandenburg.de/sixcms/media.php/9/22-09-19_Positionspapier-Wasser.pdf
• Flussgebietsbewirtschaftung Obere Havel: https://mleuv.brandenburg.de/mleuv/de/aktuelles/presseinformationen/detail/~10-05-2022-flussgebietsbewirtschaftung-der-oberen-havel
• Nationale Wasserstrategie
• Wasserstrategie Hauptstadtregion 2050

This represents a major shortcoming, as water-related challenges in Berlin-Brandenburg are inherently linked to political decision-making and institutional frameworks. Furthermore, the article aims to serve as a 'roadmap for scientists and policymakers'. However, without integration into the relevant political framework, it is unclear to what extent the identified questions can actually be addressed in terms of administration, setting priorities, and allocating resources.

1. Lack of integration with the current research landscape:

The article presents the formulated research questions in isolation from ongoing or recently completed research activities. However, there are numerous relevant projects that should discussed in the context of the questions, including Inno_MAUS, AMAREX, SpreeWasser:N, WadKlim, NITRO2, VITA-MIN,… and the CliWaC project itself. A sound contextualisation is essential to clarify:

• Which (sub-)questions have already been researched, and where do actual knowledge gaps remain?
• How can synergies between research and practice be strategically promoted?
• Which findings have already been implemented in practice?

For example, the NITRO2 project developed a decision support system for low water and drought conditions. Similarly, SpreeWasser:N produced a drought management plan and an early warning system. In this context, it is important to consider how far we have progressed in answering Q5 ('How feasible is the implementation of a multi-sector, impact-based drought monitoring and forecasting system?')?

Detailed Comments on the Article

Line 20:

Comment: The reference to Reyer et al., 2023 is missing in the list and should be added.

Lines 20–21:

Comment: The paper explicitly names floods as a relevant challenge. This makes it even more surprising that none of the ten prioritized or 48 total questions explicitly address pluvial or fluvial flooding — the term "flood" is entirely absent. The article lacks a discussion of why this topic was not considered relevant or did not emerge from the process. This omission is particularly striking given that current projects, such as Inno_MAUS, are explicitly investigating the impacts of heavy rainfall and urban flooding. A brief reflection on this gap — whether due to methodological limitations, the composition of participants, or shifting priorities — would have added important context.

Line 40ff:

Comment: A clear geographical delimitation of the study area is missing. It remains unclear whether the focus is limited to Berlin and Brandenburg or also includes neighboring regions such as Saxony's Lusatia or the Upper Havel area.

Lines 54–55:

Comment: At this point, it would be helpful to provide an initial contextualization using regional climate scenarios. Which climatic projections were considered—or deliberately not? Behind this lies a central question: Will the region become wetter or drier in the future, when (seasonally) will these changes occur, and how will groundwater recharge develop?

Lines 56ff:

Comment: The methodological description of the co-design process remains too vague. Quantitative information on key steps is missing:

• How many experts participated in phases S1 to S3?
• How many statements were generated in total—and by how many individuals?

Lines 70–71:

Comment: It is unclear how many questions were originally submitted. Who was responsible for editing, organizing, and finalizing the list of questions? The composition of the reference group is also unclear. How many people were involved? Which disciplines were represented? Was there balanced representation in terms of gender, institutions, or sectors?

Line 75:

Comment: Question Q6 received notably higher relevance scores (cf. Figure S1), whereas question Q2, for example, barely made it into the top 10. To improve the transparency and interpretability of the selection, it would be helpful to include information about the highest-scoring question as well as the spread of scores (e.g., mean, standard deviation).

Lines 80ff:

Comment: While a detailed discussion of the questions is formally not envisaged, some conceptual ambiguities arise when reading them. Two examples:

• Q1: Why are only ecosystems and agriculture addressed? Other important sectors such as drinking water supply, public health, tourism, or navigation are excluded. Furthermore, which extreme events (e.g. flood, wind) are meant that specifically affect agriculture and ecosystems (e.g. forest fires)?
• Q6: Why is the focus solely on “nature-based solutions”? Technological and infrastructural options, such as the (controversially discussed) Elbe water transfer into the Spree, are left out. An open-ended question on the combination of both approaches would be more practice-oriented.

Such considerations should be more integrated into the discussion.

Lines 83–84:

Comment: Content is repeated from Section 2.

Line 94:

Comment: Typographical error: a space is missing between two words.

Lines 100ff:

Comment: A critical discussion of potential goal conflicts—e.g. between planning certainty, procedural acceleration, and participation—would be beneficial here.

Lines 105ff:

Comment: The prioritisation process is not considered in relation to current weather events (e.g. drought versus heavy rainfall). For example: If an extreme rainfall event such as those in Münster or Copenhagen had occurred shortly before the workshop, different topics might have been prioritised.