the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Aug 2025
On the intensity and destructive potential of a past extreme, synoptic storm in a future warmer climate
Abstract. The global climate is undergoing significant changes, with rising greenhouse gas concentrations driving increased temperatures, altered precipitation patterns, and sea level rise. Yet, the full implications for mid-latitude storm systems remain an area of active investigation. This study examines how such storms may intensify under future warming, focusing on Storm Anatol, which severely impacted Denmark on 3 December 1999. Using the high-resolution weather prediction model HARMONIE-AROME and a pseudo-global warming (PGW) framework, the storm is simulated under a range of thermodynamic conditions representative of a warmer climate.
Results show a clear warming signal, with increased near-surface temperatures and atmospheric moisture contributing to stronger storm dynamics. Wind and gust speeds rise systematically with temperature, while the spatial extent and duration of damaging wind conditions also expand. To quantify these changes, we introduce the Cumulative Wind Exposure Index (CWEI), which captures the integrated spatial and temporal severity of wind exposure.
Application of CWEI reveals a marked increase in cumulative wind exposure in warmer scenarios relative to the historical case. When linked to established wind-damage relationships, this translates to substantially higher potential for structural damage and disruption. These findings suggest that storms like Anatol, already destructive in the past, are likely to become even more damaging under future climate conditions. This underscores the need for climate-resilient building standards, improved early warning systems, and long-term adaptation strategies across northern Europe.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-3173', Anonymous Referee #1, 17 Sep 2025
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AC1: 'Reply on RC1', Johanne Øelund, 14 Nov 2025
The authors would like to express sincere gratitude to the reviewers for their thorough, constructive, and insightful feedback. The comments and suggestions have greatly contributed to improving the clarity, structure, and scientific rigor of the manuscript. They have also highlighted areas for future development and refinement of this line of research.
All comments from Reviewers 1 and 2 have been carefully considered and addressed in the revised version of the manuscript. Below, each reviewer’s points are presented in the order they were raised, followed by detailed responses and a summary of the corresponding revisions.
All edits are highlighted in the revised manuscript (tracked changes), updated figures and tables are included, and supplementary figures (storm tracks and domain-wide CWEI maps) have been added.
Review #1:
General comments:
1: Some reorganization would improve the overall storyline of the manuscript. The current Theory section could be condensed and integrated into the Introduction. I also recommend moving and shortening Section 4.4 Storm damages as well as part of Section 4.2 Pseudo-global warming and storyline approach into the Introduction. Lines 123–130 may also be placed in the corresponding sections of 4.1 and 4.2. In addition, Section 2 The storm Anatol, viewed from a Danish perspective would fit better either between the Methods and Results, or within the Results section.
1: The authors agree with the reviewer that restructuring improves the logical flow of the manuscript. The following changes will be made:
- The former “Theory section” will be substantially condensed and incorporated into the Introduction, focusing on the conceptual framing relevant to the study objectives.
- Section “Storm damages” will also be moved to the Introduction, where it will provide context for the motivation for defining a cumulative wind exposure metric. This section will also be shortened to avoid redundancy.
- The description of the pseudo-global warming and storyline approach originally in Section 4.2 will be edited and relocated to Methods, where it more clearly supports the experimental design.
- The background description of Storm Anatol will be moved to directly follow the description of the model setup in Methods, aligning the meteorological context with the simulation design.
2 The manuscript would benefit from greater consistency in terminology and notation. For example: extratropical low-pressure system (Line 17), extratropical cyclone (Line 330), and extratropical storm (Line 340) are all used;
‘threshold’ and ‘limits’ are used interchangeably, including in figures;
time units are given as GMT (Lines 74, 80) and UTC (from Line 235 onward and in figure captions);
the terms (mean) wind speed and (wind) velocity are not clearly distinguished (e.g. ‘maximum mean wind speed’ vs. ‘maximum wind speed’).
In addition, it should be clarified whether Ref and Control refer to the same experiments. Ensuring consistency throughout the manuscript would improve readability.2: The authors thank the reviewer for identifying these inconsistencies. The manuscript will be thoroughly reviewed, and terminology will be standardized, using storm, threshold, control run etc.
3 It is not clear why the authors sometimes use the entire model domain and other times only the land area of Denmark to compare results. For a holistic perspective on the storm, it would be helpful to also present the numbers for the entire storm, not just Denmark.
3: The authors acknowledge the reviewer’s comment. In this study, the focus has primarily been on the storm over the land area of Denmark. We agree, however, that examining the storm in its entirety could provide additional insights. We will still highlight Denmark in terms of CWEI.
4: A limitation of your pseudo-global warming (PGW) approach is that it uniformly adds temperature, thereby neglecting projected changes in vertical temperature profiles and meridional temperature gradients. Is it possible to account for these in the experiments, or alternatively, could the authors explain why the PGW approach remains reasonable? In Line 167ff, it is stated that “a sensitivity test was conducted on vertical temperature lapse rates and the overall large-scale north-south temperature gradient.” It is not entirely clear what was done in this test. If some simulations with more realistic warming of vertical temperature profiles and north-south temperature gradients were conducted, this would be an interesting aspect and should be included or discussed in this study. A more detailed explanation of what is meant by sensitivity test would be helpful.
4: We thank the reviewer for pointing this out. The pseudo-global warming (PGW) method indeed applies a uniform temperature perturbation, which neglects projected changes in vertical lapse rates and meridional temperature gradients. We acknowledge this as a limitation of the approach. We will revise the manuscript to clarify what was done in the sensitivity test and to better explain why the PGW approach remains reasonable despite these limitations. Sensitivity test was carried out by Matte et al, Zeitzen et al, and we will provide a better clarification of this in the manuscript.
5: It is quite a strong statement to say that the overall intensity of the storm increases by using such a large domain’s maximum mean wind speed and gusts for 5 simulations (Line 242, Table 1 and Figure 3). As the author mentioned the linear relationship is not large. Is the result significant? In Table 1. It becomes evident that for the -2°C the maximum wind gust in the domain is lower than for the +1°C and almost similar to the Ref. Also, for the -1°C the max mean wind speed is higher than for the Ref and the +1°C wind gust is very similar to the +3°C. Can the author discuss this result and explain? It may also be helpful to include additional metrics for cyclone intensity for example minimum core pressure (only mentioned for Ref and +3°C) or maximum vorticity? Is the footprint of the storms changing for different warming levels?
5: We thank the reviewer for this important comment. We agree that our initial statement about an overall increase in storm intensity was too strong given the variability across simulations. The maximum domain-wide wind speeds and gusts do not exhibit a strictly monotonic response to temperature perturbation. However, when considered together, the results suggest a tendency toward higher intensities with warming: the regression yields R² = 0.78 for maximum mean wind speed and R² = 0.58 for maximum gusts. While this indicates a positive relationship, the limited number of simulations precludes a rigorous statistical assessment, and we will revise the manuscript to clarify that the results are indicative rather than conclusive, and the R² values are indicative but not statistically robust.
Specific comments:
Line 7: The authors state ‘with increased near-surface temperatures and atmospheric moisture contributing to stronger storm dynamics.’ However, in this study not only near-surface temperature, but the temperature of the entire atmosphere was modified, which makes the statement somewhat misleading. Furthermore, it is not clearly demonstrated in this study how atmospheric moisture contributes to stronger storm dynamics.
Line 7: The authors thank the reviewer for noting this. We agree that the original phrasing was misleading, as the applied PGW perturbation modified the temperature of the entire atmospheric column rather than only the near-surface layer. The sentence will therefore be revised.
Line 8: The term ‘systematically’ may be too strong, as the +2°C simulation also shows instances of lower wind speeds and gusts.
Line 8: The term will be modified.
Line 26 and Line 32: It is not clear how the reported 24m/s value relates to the 24.5m/s used as the threshold in the subsequent analysis. Could the authors clarify the reasoning behind choosing 24.5m/s later in the study?
Line 26/32: We thank the reviewer for pointing out this potential source of confusion. To clarify, the 24 m/s threshold is applied because it corresponds to the Eurocode guideline for house construction, whereas the 24.5 m/s threshold represents the meteorological definition of a storm (based on 10-min mean wind speed). We will revise the text to make this distinction clearer.
Line 33: A reference to the commonly used threshold for defining storm events is missing.
Line 33: We thank the reviewer for pointing this out, and will add the proper reference.
Line 34: Here a reference to the ‘storms of this magnitude are relatively rare’ is missing.
Line 34: Sentence will be removed, due to editing of section, should it still occur, we will make the proper reference.
Line 51: How is the study different form the cited study investigating the same storm (Zeitzen et al. 2025)? Highlight the novelty of the study more.
Line 51: The authors thank the reviewer for pointing our attention on this issues, as it is important to clarify that this paper differs from Zeitzen et al, which is more meteorological oriented in contrast to this paper being more focused on the consequences of storm and the introduction of CWEI, this will be made more clear throughout the manuscript..
Line 57: Could the authors give a brief explanation of the pseudo-global warming method, and the general idea of this approach? What are advantages of this method?
Line 57: We thank the reviewer for highlighting this, and we will explaine it briefly in the paper: The pseudo-global warming (PGW) approach is a method to assess the potential impact of climate change on specific weather events. In PGW, observed or simulated atmospheric conditions of a historical event are perturbed according to projected climate changes, typically derived from global or regional climate model ensembles. This entails adding temperature and moisture increments to the initial and boundary conditions, while retaining the large-scale circulation patterns of the original event. The main advantage of PGW is that it allows for the examination of how an individual storm or extreme event might evolve under warmer conditions without simulating the full climate system, thereby isolating the thermodynamic effects of climate change while preserving the event’s dynamical structure. The approach is computationally efficient and particularly useful for high-resolution regional models.
Line 59: ‘However, they pose certain challenges. Extreme storms are inherently unique, forming due to the precise alignment of multiple meteorological and climatological drivers (Ulbrich et al., 2009). When modifying atmospheric conditions to reflect a warmer climate, there is a risk of altering the storm’s fundamental dynamics, potentially reducing its extremity rather than amplifying it (see e.g. Matte et al. (2022)‘ may be moved to the discussion or justify why you still use this method.
Line 59: The authors agree that this belongs later in the manuscript. This text will be relocated to the Discussion, where it will be used to acknowledge limitations and motivate the sensitivity analysis section.
Line 72: Here you write ‘temperature contrasts’, perhaps write ‘temperature gradient’?
Line 72: This will be corrected. The term “temperature gradient” will be used for clarity and consistency with atmospheric dynamics terminology.
Line 76: The phrase ‘based on the simulations from HARMONIE-AROME’ introduces the simulation experiment for the first time, which makes it appear abrupt.
Line 76: The sentence will be rewritten to introduce the simulation setup more gradually and refer forward to the Methods section. The transition into discussing the modelling framework is now clearer.
Line 76: Which method was used to determine the storm track?
Line 76: We use the center of the low pressure to determine the track; this will be made clearer in the manuscript. A new figure will be introduced.
Line 68: What kind of ‘atmospheric disturbances’?
Line 68: The text will clarify the atmospheric disturbances as a surface baroclinic wave located northeast of Newfoundland and an upper-tropospheric shortwave disturbance originating from Labrador.
Line 81: Later in the results are you also using 10-minute mean wind speeds? Please clarify later, when explaining the data used.
Line 81: A clarification will be added to the paper indicating that 10-minute mean wind speed is used for consistency with DMI warning thresholds and damage estimation, and this is now explicitly stated where the wind data are introduced.
Line 126: A reference to the ERA5 is missing here.
Line 126: A reference to Hersbach et al. (2020) will be added.
Line 133: On what grid is the model simulated?
Line 133: This will be clarified explaining that the model runs on Lambert grid.
Line 136: Please state here the exact extend of the domain.
Line 136: The exact geographical domain boundaries will now be stated in the text and figure-text.
Line 140: To what is ERA5 interpolated to?
Line 140: This will be edited to state: The ERA5 data are horizontally and vertically interpolated to the HARMONIE-AROME model grid and vertical levels.
Line 143: What time period is the simulation exactly? Pleases also include hours of the start and end.
Line 143: This will be added with the simulations cover the period 2 December 1999, 22:00 UTC to 4 December 1999, 12:00 UTC.
Line 145: For better understanding move this sentence to Line 140.
Line 145: The sentence will be relocated accordingly.
Line 151: A reference is missing here.
Line 151: The reference will be added.
Line 151 to 155: This part should be mentioned in the introduction already and can be removed here.
Line 151-155: This content will be relocated to the Introduction to improve narrative flow.
Line 154: As I understand Brogli et al. (2023) also adapt geopotential and winds?
Line 154: This will be clarified in the text.
Line 159: Please expand the description of adjustment of specific humidity with one sentence, as it is an important part of your method.
Line 159: Thank you, for pointing our attention to this. One sentence will be added to expand the explanation of the humidity adjustment, with reference to the supplementary material for full details.
Line 160: ‘unmodified reference run’ refers to the ‘The control simulation uses unmodified ERA5 temperatures’ (Line 145)? Please keep consistency throughout the study to refer to the control simulation.
Line 160: This will be addressed. The manuscript will consistently refer to this experiment as the Control simulation, which uses unmodified ERA5 temperatures.
Line 164: This sentence needs further explanation to clarify its meaning. According to Matte et al. (2022), PGW-Uni differs from PGW-GCM. If I understand correctly, your study uses PGW-Uni. This distinction should be made clearer in order to avoid confusion.
Line 164: The relevant paragraph will be rewritten to specify, that this study applies a PGW-Uni approach and to explain briefly how this differs from PGW-GCM approaches.
Line 165: I don’t think you need to introduce the abbreviation for GCM.
Line 165: The abbreviation will be removed to streamline the text.
Line 171 to 184: This section is rather long and would fit better in the Introduction. Regarding the phrase ‘and identify the mechanisms responsible can be explored’ this would indeed be valuable, but it is not actually carried out in this study. In addition, the meaning of ‘primary and secondary processes driving the storm’s behavior’ is unclear. Why is this statement included here, given that the manuscript does not provide a detailed discussion of different processes leading to more intense winds? I suggest that Lines 176–180 can be moved to Section 4.1 Harmonie Model and data.
Line 171-184: The section will be shortened and moved. The broader context and motivation will be presented in the Introduction, and the Methods section will focus solely on the experimental implementation.
Line 193: Here it is not quite clear what the difference between the predefined limit and the threshold is? Can you state the number of the threshold used in this study? It would be helpful to only use ‘threshold’ or ‘limit’ throughout the study and the figures (title, caption, ...). Where do you normalize in that equation?
Line 193: The term “threshold” will be used consistently throughout the manuscript and in all figure captions. The threshold used in the study (24.5 m/s) will be explicitly stated, and the normalization step in the CWEI calculation will clearly be explained in the Methods.
Line 197 to 211: This part of the section is rather lengthy and could be shortened. Since it belongs to the Methods section, it currently contains too much discussion of literature.
Line 197-211: This section will be shortened. Only the methodological content will be retained; literature discussion will be relocated to the Introduction.
Line 212 to 229: At present, this section contains too much discussion of literature. It should either be focused more clearly on the method, explicitly describing what was done, or moved to the Introduction. The use of the power damage could then be explained in the Results section accordingly.
Line 212-229: This section will be edited, with its conceptual framing moved to the Introduction, while methodological details remain in the Methods. The application of the power-law damage relationship will be presented in the Results.
Line 234: With intensity you refer to, wind speed? Storm intensity can also be determined with minimum core pressure or maximum vorticity. Please clarify what you mean.
Line 234: The text will be revised to explicitly state wind intensity.
Line 234: Why not include the other warming scenarios?
Line 234: The full set of warming scenarios is presented in the Appendix. The Results text will more explicitly refers to these.
Line 235: msl is mean see level pressure (mslp) presumably, but please define.
Line 235: This will be corrected to mslp.
Line 237: ‘Notably, the center of the low-pressure system shifts eastward with each degree of warming’, do you refer to the peak intensity timestep of the storm? Could you plot the storm tracks of all the simulations? + Line 257: Is it possible to show the storm track for the different experiments?
Line 237+ 257: A new plot is made showing the path for all runs, and will be added to appendix. New plot showing the mslp for 3 run at different times will also be added.
Line 238: In this sentence it is not quite clear, what is meant with ‘there is’, what do you refer to here? I assume you refer to the different simulations. Maybe rephrase this sentence: ‘The central pressure of the low-pressure system at peak intensity (?) is with 952hPa slightly lower in the +3°C warming simulation compared to the Ref simulation with 954hPa.’
Line 238: Sentence will be modified to clarify.
Line 241: The model domain is not introduced, what is the extend of the model domain? Is the maximum mean wind speed from the complete simulation period or just one timestep? With mean wind components you mean 10 min averages and with gust instantaneous wind speed? How are the maximum wind gust values from the model? Are you referring to 10-minute wind speeds and 10m winds?
Line 241: The domain boundaries, averaging periods, and difference between 10-minute mean winds and gusts will be explicitly stated in the paper.
Line 245 ff: It is not quite clear what various methods described above you are exactly referring to? Maybe introduce the methods here shortly.
Line 245 ff: This referrers to a section now deleted, the method will only be described briefly.
Line 249: Figure 4, why only show the time lapse for the Danish land and not the entire storm affected area? + Line 256: How would those numbers look for the entire area the storm is affecting?
Line 249+256: The manuscript will explain the rationale for focusing on Denmark. New plot/results for a greater area will be added.
Line 261: Over what time period with what resolution are the CWEI values calculated? How many grid points are taken into account?
Line 261: Details on grid resolution, number of grid points, and accumulation period will be added.
Line 266: For what area is the maximum wind speed?
Line 266: The maximum speed used is from over land only. This will be made more clear in manuscript
Line 268: You have already introduced the abbreviation for pre-industrial (PI) in Line 129.
Line 268: The duplicate introduction of the abbreviation for pre-industrial (PI) will be removed.
Line 279: It would strengthen the manuscript to link the mechanisms that cause a storm intensification under a warmer climate. How are the different mechanisms influenced by warming, and what effects might this have on the storms? Can you provide insights into which mechanisms lead to stronger winds in your experiments? In Lines 269–271, you offer hypotheses explaining why stronger winds occur in the -1°C experiment. Extending this discussion to the other experiments, and showing which mechanisms cause the differences, would be highly informative.
Line 279: Mechanisms linking intensification to warming: The discussion of mechanisms will be expanded and clarified.
Technical Corrections, Tables and Figures
Figure 1: Please, add the extend of the model domain in the caption.
Figure 1: Caption will include the geographical extent of the model domain (lat/lon)
Figure 2: Remove the title of the figure and state the date and time in the captions of (a) and (b). What are the black contours. At the colorbar of (a) what do you mean with ‘Reference Wind Speed’?
Figure 2: Title will be removed and added to caption, black contours will be defined and colourbar text will be edited.
Table 1: What do you mean with maximum mean wind velocity (why not called speed anymore?) Mean over what time and what domain? Maximum over what time and domain? + Figure 3: Absolute maximum wind speed over what time and domain? .. wind = .., an equal sign is a bit misleading here. Typo in caption ‘pr’ → ‘per’. Table 1 mainly provides further support to the results shown in Figure 3 and can therefore be removed or integrated into Figure 3.
Figure 3 + table 1: Edited together, typo corrected, text will be modified to clarify.
Figure 4 and Figure 5: The information in the title could be put in the captions. I am wondering why only the Danish part is shown. Would be nice to see the entire storm affected area. Figures 4 and 5 basically show the same information. Consider removing Figure 4. Same applies for Figure B1 and B2. Typo in ‘colourbar’ → ‘colorbar’.
Figure 4 + 5: Spelling is standardised to British English throughout (colourbar → colourbar) as journal is European. Title will be removed and a plot will be deleted or moved to appendix..
Table 2: Percentage of what region land cover, Denmark? What is the total number of grid points used for the CWEI? Over what timeperiod was the CWEI calculated?
Table 2: The caption will clarify the region referenced (percentage of Denmark land cover), the total number of grid points used for the CWEI, and the time window over which the CWEI was computed.
Figure 6: Remove the title of the figure and put information in the caption. Why is here the 24m/s threshold displayed and not the 24.5m/s? Again, the equal sign is misleading as you state the change per/°C warming? Please add the right unit to the slope of the curve. In the caption it would be great to state over what domain and time period the CWEI was calculated. Same applies to Figure C1.
Figure 6: We will remove the title and add details in caption, Threshold will be clarified, it was a typo, units will be altered.
Figure 7: This is a nice figure to see the temporal evolution. The maximum mean wind speed was taken over what area? Denmark or model domain? Mean wind speed refers to hourly averages? Could you also plot the CWEI value at each timestep?
Figure 7: A timestep series of CWEI is not shown, as CWEI is cumulative by design. This will be described more thoroughly in the text. The domain will be stated.
Figure 8. What time period was used?
Figure 8: Caption will include the exact time period used.
All small typographical issues and citation punctuation problems raised by the reviewer will be corrected.
Line 52: Typo ‘Allan (2023) (von Storch et al., 2014)’ → ‘Allan (2023, von Storch et al., 2014)’
Line 55: Start a new sentence after ‘remain similar’
Line 62: In the citation on pair of () to much → ‘(e.g. Matte et al., 2022)’
Line 70: This citation should be in () -> ‘(e.g., Ulbrich et al. 2001)’
Line 80: In the citation one pair of () to much → ‘(e.g. Zeitzen et al., 2025)’
Line 122: ‘Data’ → ‘data’
Line 131: ‘Model’ -> ‘model’
Line 157: ‘Initial Conditions and Lateral Boundary Conditions’ → ‘initial conditions and lateral boundary conditions’
Line 167: A space missing between ‘... (Matte et al., 2022). In addition ...’
Line 178: The sentence: ‘As demonstrated in Zeitzen et al. (2025), in part due to the high resolution of the simulations.’ is incomplete.
Line 397: In the citation is a ‘]’ too much.
Citation: https://doi.org/10.5194/egusphere-2025-3173-AC1
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AC1: 'Reply on RC1', Johanne Øelund, 14 Nov 2025
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RC2: 'Comment on egusphere-2025-3173', Anonymous Referee #2, 07 Oct 2025
The authors present an analysis of Storm Anatol and how it may change under future warming using perturbed NWP experiments from the HARMONIE model. The results are of interest and build upon the array of literature on counterfactual historical storms under different climate conditions. The results are consistent with this literature, but i have several issues relating to the writing and content of this manuscript which would need to be addressed prior to publication. I have only few scientific/methodological issues, with most relating to clarity, the written content, and style of the manucsript.
My main comments are as follows:
1 - Section 3 (Theory) feels somewhat out of place and unnecessary in a manuscript of this type. Explaining theory of storm formation is well established, i was expecting something more on how climate change alters storm formation as this would directly relate to this studys findings. Consider re-writing with this information.
2 - Section 4 - you should mention that you also include SST perturbations as i initially read this as just atmospheric perturbations, which raised initial concerns for me until i saw this later in the manuscript.
3 - L179/180 - please provide some evidence for the reference run of HARMONIE being consistent with observations. It not being shown concerns me that the model has significant biases
4 - Section 4.4 - storm damages - what is the purpose of this section? You do not introduce any metric or mention anything that is used in the study (although i suspect it is for the analysis L245-248. If you are not using any storm damage metrics then this can be deleted, if you are from L245-248 then these need stating explicitly here in this section
Minor comments:
L26 - what is "basic wind speed value"? Is this a defined quantity? Could you please say more about that this is, is it a resilience measure/threshold?
L31 - i'd like to see more info on storm anatol here, or merge in the later section on the storm. Furthermore there should be some information on ETCs and how these extreme winds are associated with cyclonic systems.
L34 - how rare is "relatively rare"? This is quite a vague statement.
L38 - this section should come before the posing of the question on L36-37 as there should be initial discussion on why the climate makes storms worse before this question.
L46 - the North/South contrast is more of a tri-polar pattern. See papers by Severino et al. (2024; NHESS), Little et al. (2023; NCOMMS), Priestley et al. (2024; QJRMS)
L50 - here would be a good place for the question posed by L36-37
L59 - also the study of Ermis et al. (2024; 10.1088/2752-5295/ad4200) should be cited here and acknowledged more by the authors throughout.
L79 - are the quoted sustained winds and gusts local/station observations? if so please state this and where they occurred
Fig 1. - i think it would be good to have a panel here showing the pressure evolution and you can also then overlay the HARMONIE control and the different GWL experiments to see the impact on pressure evolution
L127 - +2°C - also here i was expecting to see that you also apply SST perturbations - modify this in the text as you mention it further along but not here
Section 4.3 - is this the first time that the CWEI has been used/introduced. If so please state that, if not please include a reference
L198 - please include a reference for the 98th percentile of wind speed statement
L203/204 - also include a citation here for the 24.5 m/s wind speed justification. My feeling is that 20m/s is more commonly used as a damage threshold so i'd be interested to know where this has come from.
Figure 2 - it would also be good to have a difference panel in (c).
L231/232 - this entire sentence can be shortened/deleted as you already have this information several times throughout the manuscript.
L234/236 - put brackets for your figure referencing
L235 - i would argue that the cyclone has already made landfall at the time due to the centre being over land. Please state that you are referring to the associated wind field with this.
L243/244 - are these r^2 values significant? Due to their being so few points I would not be sure if that is the case or not?
L236-238 - which methods are you referring to here and how did you obtain these numbers? There is no explanation as to how these values were obtained. See also major comment 4 above.
L253 - "time lapse" is this the correct wording here? Do you just mean "difference plot"?
L289/290 - the trend you quote here must surely be very uncertain due to the small number of experiments you have looked at? Does this mean that a comparison with the Hawkins et al. study is fair or valid?
L291-297 - see also Priestley et al. (2024; 10.1002/qj.4849) where changes in area were assessed and found increases of 1-2% per degC for central Europe
Citation: https://doi.org/10.5194/egusphere-2025-3173-RC2 -
AC2: 'Reply on RC2', Johanne Øelund, 14 Nov 2025
The authors would like to express sincere gratitude to the reviewers for their thorough, constructive, and insightful feedback. The comments and suggestions have greatly contributed to improving the clarity, structure, and scientific rigor of the manuscript. They have also highlighted areas for future development and refinement of this line of research.
All comments from Reviewers 1 and 2 have been carefully considered and addressed in the revised version of the manuscript. Below, each reviewer’s points are presented in the order they were raised, followed by detailed responses and a summary of the corresponding revisions.
All edits are highlighted in the revised manuscript (tracked changes), updated figures and tables are included, and supplementary figures (storm tracks and domain-wide CWEI maps) have been added.
1: Section 3 (Theory) feels somewhat out of place and unnecessary in a manuscript of this type. Explaining theory of storm formation is well established, i was expecting something more on how climate change alters storm formation as this would directly relate to this studys findings. Consider re-writing with this information.
1: We thank the reviewer for this helpful comment. We agree that the previous version of Section 3 was too general and did not sufficiently connect to the context of climate change and the results of our study. In the revised manuscript, Section 3 will be substantially rewritten to focus specifically on how large-scale thermodynamic and dynamic changes under warmer climates influence extratropical cyclone development, including changes in baroclinicity, moisture availability, latent heat release, and jet stream characteristics. This directly aligns the theoretical discussion with the interpretation of our perturbation experiments. The general description of storm formation will be moved to the Introduction for background, and redundant text will be removed.
2: Section 4 - you should mention that you also include SST perturbations as i initially read this as just atmospheric perturbations, which raised initial concerns for me until i saw this later in the manuscript.
2: We appreciate this observation. We will revise Section 4 to clearly state from the outset that the perturbation fields include both atmospheric temperature fields and sea surface temperature (SST) adjustments, following the pseudo-global warming framework. We will specify which warming increments were applied to SSTs and include a reference to the method used to ensure thermodynamic consistency.
3: L179/180 - please provide some evidence for the reference run of HARMONIE being consistent with observations. It not being shown concerns me that the model has significant biases
3: We agree that it is important to show the model’s performance for the reference case. We will include a validation comparison of the reference simulation against ERA5 reanalysis and DMI surface station observations, demonstrating that the reference run reproduces the storm track, timing of peak winds, and spatial wind intensity structure within expected performance bounds for HARMONIE and highlighting how the model is validated, as this has been done many times before.
4: Section 4.4 - storm damages - what is the purpose of this section? You do not introduce any metric or mention anything that is used in the study (although i suspect it is for the analysis L245-248. If you are not using any storm damage metrics then this can be deleted, if you are from L245-248 then these need stating explicitly here in this section
4: We thank the reviewer for pointing out this ambiguity. The section has now been removed, and the description of the Cumulative Wind Exposure Index (CWEI) used in the analysis will be moved to Methods. The damage-related discussion will be presented in the Results, where the CWEI will be interpreted in connection with storm footprint and wind intensity changes.
Minor comments:
L26 - what is "basic wind speed value"? Is this a defined quantity? Could you please say more about that this is, is it a resilience measure/threshold?
L26: The text will be rewritten to clearly define this quantity as a threshold wind speed for storm-level classification, not a structural resilience measure.
L31 - i'd like to see more info on storm anatol here, or merge in the later section on the storm. Furthermore there should be some information on ETCs and how these extreme winds are associated with cyclonic systems.
L31: Storm Anatol will be expanded to briefly describe the storm’s evolution, its associated extratropical cyclone characteristics, and links between cyclonic dynamics and extreme winds. Additional references to the ETC literature have been included.
L34 - how rare is "relatively rare"? This is quite a vague statement.
L34: The sentence will be edited out, due to refining the paper.
L38 - this section should come before the posing of the question on L36-37 as there should be initial discussion on why the climate makes storms worse before this question.
L38: Text will be reorganized; the discussion of climatic drivers will precede the research question for improved narrative flow.
L46 - the North/South contrast is more of a tri-polar pattern. See papers by Severino et al. (2024; NHESS), Little et al. (2023; NCOMMS), Priestley et al. (2024; QJRMS)
L46: The manuscript will describe the pattern as tri-polar, with references to Severino et al. (2024, NHESS), Little et al. (2023, NCOMMS), and Priestley et al. (2024, QJRMS).
L50 - here would be a good place for the question posed by L36-37
L50: The research question will be moved accordingly.
L59 - also the study of Ermis et al. (2024; 10.1088/2752-5295/ad4200) should be cited here and acknowledged more by the authors throughout.
L59: We thank the reviewer for pointed our attention to this interesting paper, It is most definitely relevant for this manuscript and the findings will be reflected in this work.
L79 - are the quoted sustained winds and gusts local/station observations? if so please state this and where they occurred
L79: Text will specify that reported sustained winds and gusts refer to the west coast and South Jutland.
Fig 1. - i think it would be good to have a panel here showing the pressure evolution and you can also then overlay the HARMONIE control and the different GWL experiments to see the impact on pressure evolution
Fig1: A new panel will be created showing the pressure evolution for the reference and perturbed experiments.
L127 - +2°C - also here i was expecting to see that you also apply SST perturbations - modify this in the text as you mention it further along but not here
L127: Text will be edited to state that SST perturbations are applied consistently with the atmospheric PGW increments.
Section 4.3 - is this the first time that the CWEI will be used/introduced. If so please state that, if not please include a reference
Section 4.3: CWEI will be explicitly stated as a novel metric introduced in this study.
L198 - please include a reference for the 98th percentile of wind speed statement
L198: Sentence will be removed during editing to streamline Methods and to avoid redundancy.
L203/204 - also include a citation here for the 24.5 m/s wind speed justification. My feeling is that 20m/s is more commonly used as a damage threshold so i'd be interested to know where this has come from.
L203/204: Text will state that 24.5 m/s is the official storm threshold, distinct from damage thresholds (commonly ~20 m/s). citation WHO
Figure 2 - it would also be good to have a difference panel in (c).
Figure 2: A difference panel is available; decision will be made to include it in the Appendix for clarity and to avoid clutter in the main text. The plot shows disturbances also due to the phase shifts in the storm events.
L231/232 - this entire sentence can be shortened/deleted as you already have this information several times throughout the manuscript.
L231/232: This will be delete to avoid repetition.
L234/236 - put brackets for your figure referencing
L234/236: Brackets will be added around figure references.
L235 - i would argue that the cyclone has already made landfall at the time due to the centre being over land. Please state that you are referring to the associated wind field with this.
L235: Text will be edited to clarify that the center of the cyclone is over land.
L243/244 - are these r^2 values significant? Due to their being so few points I would not be sure if that is the case or not?
L243/244: Text will be added noting that, due to the small number of simulations, R² values are indicative but not statistically robust.
L236-238 - which methods are you referring to here and how did you obtain these numbers? There is no explanation as to how these values were obtained. See also major comment 4 above.
L236-238: Text will be revised to describe explicitly how maximum wind and gust values were computed from the model outputs.
L253 - "time lapse" is this the correct wording here? Do you just mean "difference plot"?
L253: This will be changed to “time difference” for clarity.
L289/290 - the trend you quote here must surely be very uncertain due to the small number of experiments you have looked at? Does this mean that a comparison with the Hawkins et al. study is fair or valid?
L289/290: Text will be revised to acknowledge that trends are uncertain due to the limited number of experiments.
L291-297 - see also Priestley et al. (2024; 10.1002/qj.4849) where changes in area were assessed and found increases of 1-2% per degC for central Europe
L291-297: Citation for Priestley will be added including comments regarding this.
Citation: https://doi.org/10.5194/egusphere-2025-3173-AC2
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AC2: 'Reply on RC2', Johanne Øelund, 14 Nov 2025
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- 1
Review of “On the intensity and destructive potential of a past extreme, synoptic storm in a future warmer climate” by Oelund et al. 2025 submitted to NHESS
This study applies a pseudo-global warming approach to the extreme storm Anatol (December 1999) to investigate its destructive potential in a warmer climate. To quantify wind damage potential, the authors introduce a cumulative wind exposure index that accounts for both spatial and temporal wind exposure. The study shows increased wind damage potential under some warming scenarios; however, further work is needed to improve the robustness of the results and the readability of the manuscript. Overall, the manuscript is very interesting, fits well within the scope of the journal, and has the potential to make a valuable contribution to the literature on storms and their damage potential in a warmer climate. I do, however, have several comments that should be addressed before publication.
General comment
‘threshold’ and ‘limits’ are used interchangeably, including in figures;
time units are given as GMT (Lines 74, 80) and UTC (from Line 235 onward and in figure captions);
the terms (mean) wind speed and (wind) velocity are not clearly distinguished (e.g. ‘maximum mean wind speed’ vs. ‘maximum wind speed’).
In addition, it should be clarified whether Ref and Control refer to the same experiments. Ensuring consistency throughout the manuscript would improve readability.
Specific comments
Line 7: The authors state ‘with increased near-surface temperatures and atmospheric moisture contributing to stronger storm dynamics.’ However, in this study not only near-surface temperature, but the temperature of the entire atmosphere was modified, which makes the statement somewhat misleading. Furthermore, it is not clearly demonstrated in this study how atmospheric moisture contributes to stronger storm dynamics.
Line 8: The term ‘systematically’ may be too strong, as the +2°C simulation also shows instances of lower wind speeds and gusts.
Line 26 and Line 32: It is not clear how the reported 24m/s value relates to the 24.5m/s used as the threshold in the subsequent analysis. Could the authors clarify the reasoning behind choosing 24.5m/s later in the study?
Line 33: A reference to the commonly used threshold for defining storm events is missing.
Line 34: Here a reference to the ‘storms of this magnitude are relatively rare’ is missing.
Line 51: How is the study different form the cited study investigating the same storm (Zeitzen et al. 2025)? Highlight the novelty of the study more.
Line 57: Could the authors give a brief explanation of the pseudo-global warming method, and the general idea of this approach? What are advantages of this method?
Line 59: ‘However, they pose certain challenges. Extreme storms are inherently unique, forming due to the precise alignment of multiple meteorological and climatological drivers (Ulbrich et al., 2009). When modifying atmospheric conditions to reflect a warmer climate, there is a risk of altering the storm’s fundamental dynamics, potentially reducing its extremity rather than amplifying it (see e.g. Matte et al. (2022)‘ may be moved to the discussion or justify why you still use this method.
Line 72: Here you write ‘temperature contrasts’, perhaps write ‘temperature gradient’?
Line 76: The phrase ‘based on the simulations from HARMONIE-AROME’ introduces the simulation experiment for the first time, which makes it appear abrupt.
Line 76: Which method was used to determine the storm track?
Line 68: What kind of ‘atmospheric disturbances’?
Line 81: Later in the results are you also using 10-minute mean wind speeds? Please clarify later, when explaining the data used.
Line 126: A reference to the ERA5 is missing here.
Line 133: On what grid is the model simulated?
Line 136: Please state here the exact extend of the domain.
Line 140: To what is ERA5 interpolated to?
Line 143: What time period is the simulation exactly? Pleases also include hours of the start and end.
Line 145: For better understanding move this sentence to Line 140.
Line 151: A reference is missing here.
Line 151 to 155: This part should be mentioned in the introduction already and can be removed here.
Line 154: As I understand Brogli et al. (2023) also adapt geopotential and winds?
Line 159: Please expand the description of adjustment of specific humidity with one sentence, as it is an important part of your method.
Line 160: ‘unmodified reference run’ refers to the ‘The control simulation uses unmodified ERA5 temperatures’ (Line 145)? Please keep consistency throughout the study to refer to the control simulation.
Line 164: This sentence needs further explanation to clarify its meaning. According to Matte et al. (2022), PGW-Uni differs from PGW-GCM. If I understand correctly, your study uses PGW-Uni. This distinction should be made clearer in order to avoid confusion.
Line 165: I don’t think you need to introduce the abbreviation for GCM.
Line 171 to 184: This section is rather long and would fit better in the Introduction. Regarding the phrase ‘and identify the mechanisms responsible can be explored’ this would indeed be valuable, but it is not actually carried out in this study. In addition, the meaning of ‘primary and secondary processes driving the storm’s behavior’ is unclear. Why is this statement included here, given that the manuscript does not provide a detailed discussion of different processes leading to more intense winds? I suggest that Lines 176–180 can be moved to Section 4.1 Harmonie Model and data.
Line 193: Here it is not quite clear what the difference between the predefined limit and the threshold is? Can you state the number of the threshold used in this study? It would be helpful to only use ‘threshold’ or ‘limit’ throughout the study and the figures (title, caption, ...). Where do you normalize in that equation?
Line 197 to 211: This part of the section is rather lengthy and could be shortened. Since it belongs to the Methods section, it currently contains too much discussion of literature.
Line 212 to 229: At present, this section contains too much discussion of literature. It should either be focused more clearly on the method, explicitly describing what was done, or moved to the Introduction. The use of the power damage could then be explained in the Results section accordingly.
Line 234: With intensity you refer to, wind speed? Storm intensity can also be determined with minimum core pressure or maximum vorticity. Please clarify what you mean.
Line 234: Why not include the other warming scenarios?
Line 235: msl is mean see level pressure (mslp) presumably, but please define.
Line 237: ‘Notably, the center of the low-pressure system shifts eastward with each degree of warming’, do you refer to the peak intensity timestep of the storm? Could you plot the storm tracks of all the simulations?
Line 238: In this sentence it is not quite clear, what is meant with ‘there is’, what do you refer to here? I assume you refer to the different simulations. Maybe rephrase this sentence: ‘The central pressure of the low-pressure system at peak intensity (?) is with 952hPa slightly lower in the +3°C warming simulation compared to the Ref simulation with 954hPa.’
Line 241: The model domain is not introduced, what is the extend of the model domain? Is the maximum mean wind speed from the complete simulation period or just one timestep? With mean wind components you mean 10 min averages and with gust instantaneous wind speed? How are the maximum wind gust values from the model? Are you referring to 10-minute wind speeds and 10m winds?
Line 245 ff: It is not quite clear what various methods described above you are exactly referring to? Maybe introduce the methods here shortly.
Line 249: Figure 4, why only show the time lapse for the Danish land and not the entire storm affected area?
Line 256: How would those numbers look for the entire area the storm is affecting?
Line 257: Is it possible to show the storm track for the different experiments?
Line 261: Over what time period with what resolution are the CWEI values calculated? How many grid points are taken into account?
Line 266: For what area is the maximum wind speed?
Line 268: You have already introduced the abbreviation for pre-industrial (PI) in Line 129.
Line 279: It would strengthen the manuscript to link the mechanisms that cause a storm intensification under a warmer climate. How are the different mechanisms influenced by warming, and what effects might this have on the storms? Can you provide insights into which mechanisms lead to stronger winds in your experiments? In Lines 269–271, you offer hypotheses explaining why stronger winds occur in the -1°C experiment. Extending this discussion to the other experiments, and showing which mechanisms cause the differences, would be highly informative.
Technical Corrections, Tables and Figures
Figure 1: Please, add the extend of the model domain in the caption.
Figure 2: Remove the title of the figure and state the date and time in the captions of (a) and (b). What are the black contours. At the colorbar of (a) what do you mean with ‘Reference Wind Speed’?
Table 1: What do you mean with maximum mean wind velocity (why not called speed anymore?) Mean over what time and what domain? Maximum over what time and domain?
Figure 3: Absolute maximum wind speed over what time and domain? .. wind = .., an equal sign is a bit misleading here. Typo in caption ‘pr’ → ‘per’. Table 1 mainly provides further support to the results shown in Figure 3 and can therefore be removed or integrated into Figure 3.
Figure 4 and Figure 5: The information in the title could be put in the captions. I am wondering why only the Danish part is shown. Would be nice to see the entire storm affected area. Figures 4 and 5 basically show the same information. Consider removing Figure 4. Same applies for Figure B1 and B2. Typo in ‘colourbar’ → ‘colorbar’.
Table 2: Percentage of what region land cover, Denmark? What is the total number of grid points used for the CWEI? Over what timeperiod was the CWEI calculated?
Figure 6: Remove the title of the figure and put information in the caption. Why is here the 24m/s threshold displayed and not the 24.5m/s? Again, the equal sign is misleading as you state the change per/°C warming? Please add the right unit to the slope of the curve. In the caption it would be great to state over what domain and time period the CWEI was calculated. Same applies to Figure C1.
Figure 7: This is a nice figure to see the temporal evolution. The maximum mean wind speed was taken over what area? Denmark or model domain? Mean wind speed refers to hourly averages? Could you also plot the CWEI value at each timestep?
Figure 8. What time period was used?
Line 52: Typo ‘Allan (2023) (von Storch et al., 2014)’ → ‘Allan (2023, von Storch et al., 2014)’
Line 55: Start a new sentence after ‘remain similar’
Line 62: In the citation on pair of () to much → ‘(e.g. Matte et al., 2022)’
Line 70: This citation should be in () -> ‘(e.g., Ulbrich et al. 2001)’
Line 80: In the citation one pair of () to much → ‘(e.g. Zeitzen et al., 2025)’
Line 122: ‘Data’ → ‘data’
Line 131: ‘Model’ -> ‘model’
Line 157: ‘Initial Conditions and Lateral Boundary Conditions’ → ‘initial conditions and lateral boundary conditions’
Line 167: A space missing between ‘... (Matte et al., 2022). In addition ...’
Line 178: The sentence: ‘As demonstrated in Zeitzen et al. (2025), in part due to the high resolution of the simulations.’ is incomplete.
Line 397: In the citation is a ‘]’ too much.