The role of preconditioning for extreme  storm surges in the western Baltic Sea

Andrée, Elin; Su, Jian; Dahl Larsen, Morten Andreas; Drews, Martin; Stendel, Martin; Skovgaard Madsen, Kristine

doi:https://doi.org/10.5194/nhess-23-1817-2023

Articles | Volume 23, issue 5

https://doi.org/10.5194/nhess-23-1817-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Coastal hazards and hydro-meteorological extremes

https://doi.org/10.5194/nhess-23-1817-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 5

Research article

|

15 May 2023

Research article |

| 15 May 2023

The role of preconditioning for extreme storm surges in the western Baltic Sea

Elin Andrée, Jian Su, Morten Andreas Dahl Larsen, Martin Drews, Martin Stendel, and Kristine Skovgaard Madsen

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Final revised paper (published on 15 May 2023)
Preprint (discussion started on 30 May 2022)

Interactive discussion

Status: closed

RC1:
'Comment on nhess-2022-149', Anonymous Referee #1, 29 Jun 2022

The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2022-149/nhess-2022-149-RC1-supplement.pdf

Citation: https://doi.org/10.5194/nhess-2022-149-RC1
- AC1: 'Reply on RC1', Elin Andree, 23 Aug 2022
  
  The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2022-149/nhess-2022-149-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/nhess-2022-149-AC1
RC2:
'Comment on nhess-2022-149', Anonymous Referee #2, 10 Jul 2022

This study is a nice example of exploration of potential changes to the existing catastrophic events in future climates. It is based on the perception that extremely dangerous situations in the Baltic Sea are usually formed by a sequence of episodes that are dynamically connected in time rather than a combination of basically random reactions of the sea to various forcing components that are governed by some extreme value distribution. This is a reasonable way forward in the Baltic Sea conditions where the sea level “climate” of several sub-basins may contain statistically almost impossible outliers.

The analysis is sound and professional. All aspects of the modeling efforts have been explained in detail so that even an inexperienced in modeling reader can enjoy the line of thoughts and catch the main points. The use of English and technical aspects of the manuscript are fine. The outcome is carefully justified and the formulated conclusions fully supported.

Therefore, I recommend the manuscript for publication basically as it is.

However, there are some fairly minor items, adjustment of which may make the presentation even better. Only one issue definitely needs clarification for inexperienced readers: sea level elevations propagate in many occasions as (long) waves, so what moves is wave energy rather than water mass.

Abstract, line 4: it would be better to say “prior conditions may influence”.

Line 6: consider saying “certain” instead of “different”.

Line 7: consider saying “increase in the water level of 36 cm”.

Line 9: it is strongly recommended to say “water mass distributions propagate as (long) waves” (I guess this meant).

Page 2, lines 40–46: it might be useful to mention also wave-driven set-up that may in some occasions provide up to 1/3 of the total surge.

Page 4, line 95: it might be more appropriate to speak about “more unfavourable” preconditioning here, on line 114 and on page 15.

Line 117: from the presentation it seems that “at least two weeks” would be more exact.

Line 121: winds probably caused “intense net transport”.

Lines 121–122: “the maximum …. peaked” sounds strange.

Line 125: as mentioned above, the release of piled-up waters normally occurs in the form of a (long) wave. This wave travels to the southwest while water velocities in it are fairly small (I guess on the order of 10 cm/s); thus “flow” is conceptually incorrect.

Line 141: DWD was already explained.

Line 152: check “methods … is described".

Page 6, Caption to Fig. 1: check “forcing … are”.

Page 8, line 197: The water level was exceptionally high also in the Gulf of Finland. Soomere and Pindsoo (2016, Continental Shelf Research, 115, 53–64, doi: 10.1016/j.csr.2015.12.016) visualised modelled water levels above 80 cm near Tallinn for more than a week in March 1990.

Page 12, line 282: correct “Landort”.

Line 304: as above, it was motion of wave (energy), not really flow of water masses.

Page 13, caption to Fig. 4: correct “capitol”.

Page 15, lines 338–343: I guess that this almost linear dependence may partially reflect the way how surface drag is calculated from the wind speed. I guess that readers would appreciate a short comment on that.

Page 17, lines 363–364: it may make sense to add that a decrease in salinity in the Baltic Sea may add to the sea level rise signal at the entrance of Danish straits.

Citation: https://doi.org/10.5194/nhess-2022-149-RC2
- AC2: 'Reply on RC2', Elin Andree, 23 Aug 2022
  
  The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2022-149/nhess-2022-149-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/nhess-2022-149-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Reconsider after major revisions (further review by editor and referees) (09 Oct 2022) by Joanna Staneva

AR by Elin Andree on behalf of the Authors (18 Nov 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (12 Jan 2023) by Joanna Staneva

RR by Anonymous Referee #1 (23 Jan 2023)

Suggestions for revision or reasons for rejection

Dear Editor
I think the quality of the manuscript has much improved; the revised paper is much clearer.
However, please note there are a few comments that the Authors have not yet addressed:
- Line 6: the paragraph in the Authors’ reply does not match that in the revised text, i.e., “historically observed circumstances” vs. “antecedent circumstances”
- From line 23 on: I still believe that the examples about wildfires and landslide are not relevant for the research, which is indeed about sea levels and coastal hazards. Anyway, if you want to leave those in the text, please at least add “[…] from days to months or even years, depending on the event considered”
- Figure 1 is too busy. I know I am being picky about this, but it is crucial that it is clearer to fully understand what is being discussed further on in the paper. Perhaps the close-up’s size could be increased, and Authors could use different colors to label cities, islands, and straights
- Authors claim they modified Figure 1 (now Figure 2) according to my suggestions, but it doesn’t look so. Same for Figure 5 (Figure 4 in the first version of the manuscript), which has not been modified
- Perhaps it would be easier to understand Figure 3 if Authors clearly specified why they used different preconditioning periods between the scenarios FLs and S in Sect. 2.2.1.
Besides, I still think that the English grammar still needs a thorough check before the paper is accepted for publication. See below a few typos:
- At line 4: you cannot say “may influence” as the event occurred in the past, rather you should say “[…] different prior conditions may had influenced peak […]”
- The term “precondition” is widely used and recurrent in the text, though I have never heard it before in the context of geophysical studies. As such, I wonder whether it is appropriate (if so, just overlook this comment and move ahead but please check this out)
- Line 8: was the increase modelled, or it was observed? You say that it “occurred” after saying “simulated”, which is totally confusing
- Line 65: I am not sure that “propose” is well suited there. Perhaps “suggest”?
- Line 135: “during the original experiment, i.e., for” should be replaced with “for”. Actually, you did not make an experiment, so the term is not appropriate
- Line 167: remove commas after “we” and “therefore”
- Line 309: this whole sentence is still unclear to me: “we assess the entire observation period (1886-2021) and each scenario for the occurrence pattern between elevated sea levels and their corresponding duration”. What is that you are assessing?

I am not a native speaker so the list above is very limited, but as I said the whole text should be reviewed.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (19 Mar 2023) by Joanna Staneva

AR by Elin Andree on behalf of the Authors (29 Mar 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Mar 2023) by Joanna Staneva

ED: Publish as is (08 Apr 2023) by Piero Lionello (Executive editor)

AR by Martin Drews on behalf of the Authors (15 Apr 2023)

Short summary

When natural processes interact, they may compound each other. The combined effect can amplify extreme sea levels, such as when a storm occurs at a time when the water level is already higher than usual. We used numerical modelling of a record-breaking storm surge in 1872 to show that other prior sea-level conditions could have further worsened the outcome. Our research highlights the need to consider the physical context of extreme sea levels in measures to reduce coastal flood risk.