| 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.
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.