the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Jun 2026
Past and future European atmospheric extreme events under climate change – the ClimXtreme program's structure and results
Abstract. The meteorological extreme events heatwaves, droughts, heavy precipitation, floods and wind storms affect socio-economic systems and generate considerable attention. The role of anthropogenic climate change in the generation, frequency, and severity of observed and future events triggers mitigation and adaptation questions. Weather-related extremes are rare and embedded into atmospheric dynamics. This sets the frame for a dynamical-statistical analysis coupled to detailed impact or risk studies of rare events. This approach is taken by the German Federal Ministry BMBFTR funded project ClimXtreme-1 with 35 sub-projects. Here we compile the contributions of 21 articles of the inter-journal NHESS/ASCMO/WCD special issue. We connect them to 33 peer reviewed ClimXtreme-1 writings in other journals. For archetypic events over continental areas in mid Europe the individual research results are reported. These involve the use of existing and newly developed indices, analyses of the atmospheric dynamics and process-based chains using global and regional climate models results and statistical detection and attribution studies, with emphasis on establishing a causal relationship between extreme events and anthropogenic climate change. Two overarching conclusions emerge from the joint appraisal of the ClimXtreme-1 publications. Firstly, conclusions on causality show that the attribution analyses of observed events demonstrate the necessary contribution of past anthropogenic climate change to the event while sufficient contributions to future extremes need to be established. Secondly, findings from the dynamic process studies highlight the need to expand the current attribution approaches (statistical vs. storyline) to include the mediator-moderator framework.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Natural Hazards and Earth System Sciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2697', Anonymous Referee #1, 26 Aug 2026
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RC2: 'Comment on egusphere-2026-2697', Anonymous Referee #2, 07 Sep 2026
This manuscript synthesizes findings from the first phase of the ClimXtreme programme, drawing on 21 special-issue articles and 33 additional publications. It addresses heatwaves and droughts, heavy precipitation and floods, and extratropical cyclones and windstorms, linking physical processes, statistical methods, attribution, and socioeconomic impacts. The manuscript provides a useful overview of a substantial collaborative research effort. However, its contribution beyond a descriptive summary of individual publications needs strengthening. In particular, the geographical scope, interpretation of causal necessity and sufficiency, and evidential basis for the mediator–moderator framework require clarification.
Major comments
1.The geographical scope of the title exceeds that of much of the evidence presented.
The title suggests a synthesis of European atmospheric extremes, whereas many of the detailed examples concern Germany and Central Europe, particularly the 2018 hot–dry conditions, the 2017 Berlin precipitation event, and the July 2021 flooding. Although some reviewed studies have a broader European domain, the manuscript does not consistently distinguish continental findings from regional results.
2. Connect the conclusions more directly to the questions posed in the Introduction.
Section 1.1 asks whether past climate change has increased extreme events and how future climate change may affect them. However, the Conclusions focus mainly on methods and conceptual frameworks. Please return explicitly to these two questions and summarise what the reviewed studies establish for each hazard, including where an answer remains uncertain.
3. Use a more consistent structure for the hazard-specific sections.
The heatwave and drought section introduces indices before discussing an event, the precipitation section gives considerable attention to methods and case studies, and the windstorm section follows a different organisation. A common sequence would make comparison easier: the main research question, principal findings, an illustrative example, and remaining limitations.4. Meteorological hazards, actual impacts, and compound events should be distinguished more clearly.
Although Section 2.3 acknowledges the importance of exposure and vulnerability, the subsequent discussions of insurance losses, forest damage, and agricultural yield reductions do not consistently explain how these factors influence the interpretation of impacts. For example, higher losses associated with compound wind–precipitation events do not, by themselves, demonstrate a synergistic effect beyond the effects of the individual hazards. Such differences could also reflect variations in wind speed, affected area, or asset exposure. The authors should clarify whether and how the underlying studies controlled for these factors.
5. Introduce the recurring conceptual terms more clearly.
Terms such as “mediator,” “moderator,” “necessity,” and “sufficiency” recur throughout the manuscript and occupy a prominent place in the conclusions. Their practical relevance may nevertheless be difficult to follow for readers outside attribution research. Please introduce them with one simple example and explain how they help interpret the studies reviewed. A conceptual figure could provide a useful reference and reduce repeated explanations.
Minor comments
1. The two overarching research questions should be formulated more neutrally.
The questions appear to presuppose a causal relationship in which climate change modifies extreme weather events. However, extreme events arise from complex dynamical and thermodynamic processes and occur within an evolving climatic background. Unless the manuscript explicitly defines and tests the relevant causal relationships, it would be more appropriate to formulate the questions in terms of how the statistical characteristics of extreme events have evolved in the context of the observed changing climate and how they are projected to evolve under different future climate scenarios. For example, the authors could ask: “What changes in the frequency, intensity, duration, and spatial extent of extreme weather events have been observed in the context of a changing climate?” and “How are these characteristics projected to evolve under different future climate scenarios?” Such wording avoids presupposing causality and more accurately reflects the descriptive and projection-based evidence synthesized in the manuscript.
2. Table 1 should provide more complete definitions of the indices.
The table provides only the index names and references, while key information such as definitions, units, thresholds, temporal scales, and reference periods is missing. This is particularly important because indices such as SPEI, HWMId, UTCI, and the compound-event indices can be calculated using different accumulation periods or thresholds, which may affect the interpretation and comparability of the reported results. Please add concise definitions and the relevant methodological settings for each index. The authors should also use “Standardized Precipitation Evapotranspiration Index” consistently as the full name of SPEI.
3. The statistical basis of return periods and event rankings should be specified.
In Section 3.2, statements concerning the 100-year return level, the event ranked as the fourth most extreme, and its classification as one of the five most severe events of the past 70 years should specify whether the estimates refer to individual stations or spatially aggregated regions, as well as the precipitation accumulation period and extremeness index used. Rankings derived from different spatial or temporal scales, event definitions, or indices should not be presented as directly comparable.
Citation: https://doi.org/10.5194/egusphere-2026-2697-RC2
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- 1
This manuscript provides a broad overview of the ClimXtreme-1 program and synthesizes 21 papers from the inter-journal special issue together with 33 related peer-reviewed publications. It covers heatwaves and droughts, heavy precipitation and floods, wind storms, event attribution, impact studies, and the shared XCES infrastructure. The manuscript is potentially useful as a reference for readers interested in European weather extremes, and the attempt to connect process understanding with probabilistic and storyline attribution is interesting. However, although the paper tried to make several broad project-level and causal conclusions, the paper is poorly organized and it is more of a collection of individual research reports, without sufficient synthesis and summary. The basis of the synthesis, the scope of the review, and the reproducibility of the presented resources need to be explained more clearly. The following comments may help improve the manuscript.The paper should try to illustrate adequate innovation achievements briefly and seriously, as this is seemingly pan-European cooperation and your government surely support you a lot. Overall, this manuscript requires greatly major revisions before it is suitable for publication.
Major Concerns
--Try to improve the Introduction section carefully
The “1.1 Scientific Background” herein is not necessary, as the background of ClimateExtreme has been illustrated below. Please simplify or remove it.
Figure 1 should be removed or move to the supplementary file. Make no sense herein.
The “1.2 The ClimXtreme Project” is worthy of being introduced as much as possible, particular for perspectives and highlights. Therefore, I suggest this sub-section should be treated carefully, introduced briefly (as the whole paper illustrate them) and divided into several parts.
--section 2
Several sketch maps or workflow is important in this section rather than verbose paragraphs.
According to Line 114, “the process” in caption of section 2.1 is referred to as near-surface process. However, Line 14 in Abstract claimed the “dynamic process studies”, but throughout the paper, there are no enough evidence for conclusion of dynamic processes, therefore, please weaken it.
--section 2.4
Please list data bases including detailed information as specific as possible (user-friendly), rather than many literature reviews and Figure 2.
--Section 3: Transparency of the literature synthesis & Lack of research highlight
Section 3 states that the manuscript provides a comprehensive summary of 21 special-issue papers and 33 papers published elsewhere. However, as the section title is Hazard-specific research highlights, neither explicit and brief highlights, nor sufficient synthesis, are displayed. In addition, Lines 260-315 are redundant because each hazard has been illustrated below. Please simplify it.
Some indices in Table 1 are common sense rather than unique for the ClimateExtreme projects, please only list the newly proposed and robust indices in Table 1.Section 3.3 “3.3 Extratropical Cyclones” is not mentioned in Line 291.
--Geographic and hazard scope should be made consistent
The title refers to European atmospheric extremes, whereas many parts of the paper focus more narrowly on Germany or Central Europe. In addition, the introduction names four WCRP archetypes, including severe convective storms, but Section 3 is organized into three main hazard groups, with convective storms and floods included only within other sections. The heatwave and drought section also contains a detailed index table that has no parallel for heavy precipitation or wind storms. Please define the geographic and hazard scope at the beginning, explain the grouping choices, and use a more parallel structure across the hazard sections. If the available literature is uneven among hazards, this imbalance should be stated as a limitation of the synthesis.
Minor Issues
--Line 5: Check throughout the manuscript, use ClimXtreme-1 or ClimXtreme
--Number of conclusions and project outputs
The abstract says that two overarching conclusions emerge, whereas Section 4 presents three. The counts of 35 sub-projects, 54 research publications, two data publications, 21 special-issue papers, and 33 papers in other journals should also be checked and explained consistently.
--Presentation and definitions in Table 1
Table 1 would be clearer if it were reformatted as a standard three-line table, using only a top rule, a rule below the header, and a bottom rule, without vertical lines or excessive internal borders. Please also align the index names and references consistently and define abbreviated entries such as "n days" and "n events" more precisely. The full name of SPEI should be checked; it is normally written as the Standardized Precipitation Evapotranspiration Index. The table caption could specify whether the table is intended to be a complete inventory of ClimXtreme indices or only a selection.