Preprints
https://doi.org/10.5194/nhess-2022-223
https://doi.org/10.5194/nhess-2022-223
09 Sep 2022
 | 09 Sep 2022
Status: this preprint is currently under review for the journal NHESS.

Improvements to the detection and analysis of external surges in the North Sea

Alexander Müller, Birgit Gerkensmeier, Benedikt Bratz, Clemens Krautwald, Olaf Müller, Nils Goseberg, and Gabriele Gönnert

Abstract. External surges are a key component of extreme water levels in the North Sea. Caused by low pressure cells over the North Atlantic and amplified at the continental shelf, they can drive water level changes of more than one meter at the British, Dutch and German coast. This work describes an improved and automated method to detect external surges in sea surface time histories. The method is used to analyse tide gauge and meteorological records from 1995 to 2020 and to supplement an existing dataset of external surges, which is used in the determination of design heights of coastal protection facilities. Furthermore, external surges are analysed with regard to their annual and decadal variability, corresponding weather conditions and their interaction with storm surges in the North Sea. 33 % of the 101 external surge occur within close succession of each other, leading to the definition of serial external surges, in which one or more external surges follow less than 72 h after the previous external surge. These serial events tend occur more often during wind–induced storm surges. Moreover, the co–occurrence with a storm surge increases the height of an external surge by 15 % on average, highlighting the importance of the consideration of combined events in coastal protection strategies. The improved dataset and knowledge about serial external surges extend the available basis for coastal protection in the North Sea region.

Alexander Müller et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2022-223', Anonymous Referee #1, 22 Nov 2022
    • AC1: 'Reply on RC1', Alexander Müller, 06 Feb 2023
  • RC2: 'Comment on nhess-2022-223', Anonymous Referee #2, 04 Jan 2023
    • AC2: 'Reply on RC2', Alexander Müller, 06 Feb 2023

Alexander Müller et al.

Alexander Müller et al.

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Short summary
External surges in the North Sea are caused by low pressure cells travelling over the Northeast Atlantic. They influence extreme water levels on the German coast and have to be considered in the design process of coastal defence structures. This study collects data about external surges from 1995–2020 and analyses their causes, behaviour and potential trends. External surges often occur less than 72 h apart, enabling a single storm surge to be influenced by more than one external surge.
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