the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Jan 2026
A High-Resolution Framework for Urban Pluvial Flood Risk Mapping
Abstract. This study presents a high-resolution framework for assessing climate-related risk at the building scale by operationalizing the IPCC risk concept, defining risk as a function of vulnerability, exposure and hazard. The framework focuses on pluvial flood risk related to people’s well-being and mobility. Hazard is driven by a 100-year rainfall event (36 mm h-1), modelled with a hydrodynamic flood simulation incorporating topography, drainage capacity, and land use. Exposure is differentiated by impact type, considering residents on ground floors for well-being and building proximity to flooded streets for mobility and accessibility. Social vulnerability is quantified using socioeconomic indicators such as age, income, and education. The framework is demonstrated using empirical data from Hamburg, Germany, identifying risk hotspots where high social vulnerability coincides with elevated flood exposure. To support practical implementation, we introduce a Python-based ArcGIS pluvial flood risk toolbox that enables automated, building-level risk mapping. The transparent and flexible design makes the framework transferable to other cities, supporting climate adaptation planning and risk-informed decision-making.
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Status: open (until 23 Feb 2026)
- RC1: 'Comment on egusphere-2025-6362', Anonymous Referee #1, 29 Jan 2026 reply
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RC2: 'Comment on egusphere-2025-6362', Anonymous Referee #2, 03 Feb 2026
reply
This manuscript presents a methodological framework for pluvial flood risk assessment at the building scale, implemented through a Python‑based ArcGIS toolbox. The concept is relevant and timely, given increasing interest in high‑resolution urban flood risk mapping. The paper is clearly written and well structured, and the availability of a toolbox has potential practical value for practitioners. From a hydrology and hazard perspective, however, several important clarifications are needed. Below I list my major and minor comments.
The manuscript repeatedly references von Szombathely et al. (in review) as a source of input data preparation and methodological details. A manuscript under review may not be accessible by readers, and might not be accepted. Critical methodological information should be described directly in this paper. In particular, the description of synthetic input data (paragraph 85) should be expanded.
The text states that synthetic building-level data were created and disaggregated from statistical-unit data. Please describe in more detail the disaggregation method and how many realizations are possible and whether the one shown is representative. Building-level risk estimates can convey a false sense of precision, especially when nearly all inputs originate from coarser administrative units
The manuscript states the chosen indicators (children <10, elderly singles, no diploma, welfare recipients), but does not justify why these were selected. Were other indicators evaluated? Why were these four selected? If the rationale is only documented in the “in review” paper, then that rationale must be reproduced here
Out of curiosity, should building characteristics such as basements used for parking/storage be considered in exposure? Basement flooding is one of the most common and damaging manifestations of pluvial flooding in cities, and it affects both mobility and well‑being.
Paragraph 120 describes the hazard layer as a 36 mm/h event representing a 100‑year storm, but essential information is missing. What is the duration of the rainfall? One hour? A design storm? Is the relevant metric rain intensity or resulting water depth? How were water depths obtained: which hydrodynamic/hydrological model was used? What are the limitations of that model? Does the simulation incorporate drainage system performance, clogged inlets, infiltration assumptions, etc.? This paragraph should be split and expanded. The hazard component is currently under‑described
Paragraph 125 raises an important methodological limitation. It would be very valuable to include (even briefly) a discussion of how results would differ if building‑level socio‑economic and exposure data were actually available. Could the authors identify a case study with real building-level data to compare against their disaggregation? If not, please discuss the sensitivity of the results to data resolution, since this goes to the heart of the paper’s novelty claim.
Regarding Figure 1. Consider adding an additional panel showing only buildings and roads without flooding to improve readability. Clarify what “building type” means (residential? mixed-use? other categories?).
The manuscript cites the IPCC risk definition from 2014. However the 2021 IPCC report provides updated terminology. The paper does not address climate change explicitly, so invoking IPCC terminology may seem unnecessary. Please clarify why the IPCC framework is emphasized, and whether the 2021 definitions are more appropriate.
Hazard section 3.1.3. The paragraph does not clearly connect the earlier mention of the 36 mm/h design storm with the hazard thresholds (30–100 cm).
Possible typo in Equation 11
Figure 2: “capacity” is misspelled.
The manuscript presents a promising framework but requires major revisions to improve, methodological clarity, and reproducibility , especially regarding hazard modeling and the implications of disaggregating socio‑economic and exposure data to building scale.
Citation: https://doi.org/10.5194/egusphere-2025-6362-RC2
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- 1
The study presents a transparent and adaptable framework for calculating pluvial flood risk at the building scale in Hamburg. The authors explicitly include social vulnerability as a risk component, which is in line with the IPCC risk framework. In that sense, the research contributes a relevant empirical and methodological contribution to assessing risk at a high resolution.
It is positive that the authors make their assumptions and modelling choices transparent and follow the FAIR principles.
The manuscript follows a clear structure and is well written (some minor typos and wording choices aside).
While the manuscript has notable strengths, I identify three main issues that require revision before publication.
However, I see three main points that need to be addressed in the manuscript.
Major concerns:
First, the manuscript would benefit from clarifying what the risk levels calculated here would translate to in a real event. The authors make it transparent that all risk components are context-dependent and their distribution is linked to the spatial scale and the distribution of input variables. However, it is not clear to me what a possible outcome of the risk levels would mean: loss of life, disruptions of livelihoods, material damages?
And second, the transferability of the approach should be discussed in more depth. The authors argue that their toolbox could be used in other contexts. They should be more explicit here. Since the toolbox requires detailed and high resolution input data (which many cities globally do not have the capacity to record and make available), the applicability is limited to context where these data (or similar data) are available. The authors should explicitly state in which kinds of contexts the toolbox is applicable (only in Germany, only in Europe, only in Hamburg, or could this toolbox be used in Nairobi, Tokyo, or Manila?), and who the intended user is. Is the approach more an academic mapping exercise or do the authors think it could be used in disaster relief and adaptation planning, and if so, how?
Lastly (and related to the first and second point), the modelling output should be validated in some way. While the sensitivity analysis is an important validation step, some kind of ground-truthing or expert elicitation would greatly benefit the claims of applicability and transferability made in the manuscript. Essentially, the authors should give some kind of qualitative assessment of what the results mean in the context of Hamburg/ their specific study area, and how the results enable decision-oriented risk management.
Recommendations for the introduction:
I think all three of these points should already be addressed in the introduction. Here, I suggest to also add a paragraph describing the study area in more detail, as well as discuss past or projected pluvial flood events including outcomes (losses and damages).
I further suggest to add a paragraph on social vulnerability and where the conceptualizing used in this research is located in the scientific debate (I am specifically missing Susan Cutter's work here, but there are others who have extensively written on household-level vulnerability). A clearer conceptualization of vulnerability would also be beneficial in justifying the choice of input variables for the SV index. I suggest briefly discussing the main intellectual conceptualizations of vulnerability (political economy/ ecology, risk-hazard, ecological resilience) and where the present research positions itself. I highly recommend Susan Cutter's 2024 paper on 'The origin and diffusion of the social vulnerability index (SoVI) as a point of reference.
The introduction has relatively generic and could present the argument more clearly. I suggest to not put too much emphasis on increasing global urbanization, but rather Hamburg-specific urbanization and risk trends (past and projected). Again, explicitly making clear in which context(s) the study is set would benefit the manuscript.
I recommend also adding a few sentences on the hazard type chosen (why pluvial flooding, why not storm surges)?
Recommendations for methods and discussion:
In the methods section or perhaps the discussion, the authors should explicitly state why they are choosing these specific vulnerability indicators and not others (is this a data availability choice or grounded in a clear theoretical framework).
The discussion would benefit from a qualitative interpretation of what 'very high pluvial flood risk to well-being' would translate to on the ground. It is unclear to me what kinds of losses and damages very high risk would entail here. An example of a past pluvial flood and its effects could help illustrate the magnitude of risk. In line 398, the authors note that "On the one hand, the relative risk assessment is a limitation, as the value itself cannot be
interpreted (see also Russo et al. 2019)." This presents a significant limitation that warrants further attention. I suggest to revise the manuscript in a way that makes it clear to the reader what the risk calculated here would translate to in a real event.
Minor points:
- The last sentence of the introduction mentions inclusive flood risk planning - was is meant by that? Just based on this statement, the reader would expect the SV index to include specific indicators for marginalized groups (people with disabilities, migrants, etc.) - this is not the case, so in what sense is this approach facilitating inclusive risk management?
- The indicator "people who have left school without a high school diploma within the past three years" is ambiguous - are these people who left school at some point in the past and have not gained a high school diploma or people who have left school within the past 3 years and not gained a high school diploma? Also, it should be made clear what this corresponds to the in German education system (Abitur? Mittlere Reife?)
- The case study area should be described in a little more detail. Which area of the city was chosen and why? Pluvial flood risk is not equally distributed in the city of Hamburg, so indicators of local risk drivers should be explicitly discussed.
- It is not clear to me how Bourdieu, 1984 is relevant to constructing indicators of sensitivity and coping capacity. (line 150: " It is important to ensure that horizontal social distinctions (such as age) contribute to sensitivity, while vertical distinctions (such as income) (Bourdieu, 1984) influence coping capacity.").
- In line 208, the authors mention first floors are assumed to be used commercially. The wording here is ambiguous, and I assume the authors mean the ground floor?
I recommend major revisions.The manuscript presents a valuable methodological contribution, but the three issues outlined above - clarifying what risk levels translate to in practice, demonstrating transferability with appropriate caveats, and providing some form of validation - must be substantively addressed before the paper is suitable for publication. I am looking forward to reviewing the revised manuscript!