Preprints
https://doi.org/10.5194/egusphere-2023-820
https://doi.org/10.5194/egusphere-2023-820
26 Apr 2023
 | 26 Apr 2023

Uncertainties and discrepancies in the representation of recent storm surges in a non-tidal semi-enclosed basin: a hind-cast ensemble for the Baltic Sea

Marvin Lorenz and Ulf Gräwe

Abstract. Extreme sea level events, such as storm surges, pose a threat to coastlines around the globe. Many tide gauges have been measuring sea level and recording these extreme events for decades, some for over a century. The data from these gauges often serve as the basis for evaluating the extreme sea level statistics, which are used to extrapolate sea levels that serve as design values for coastal protection. Hydrodynamic models often have difficulty in correctly reproducing extreme sea levels and, consequently, extreme sea level statistics and trends. In this study, we generate a 13-member hind-cast ensemble for the non-tidal Baltic Sea from 1979 to 2018 using the coastal ocean model GETM (General Estuarine Transport Model). In order to cope with mean biases in maximum water levels in the simulations, we include both simulations with and without wind speed adjustments in the ensemble. We evaluate the uncertainties in the extreme value statistics and recent trends of annual maximum sea levels. Although the ensemble mean shows good agreement with observations regarding return levels and trends, we still find large variability and uncertainty within the ensemble (95 % confidence levels up to 60 cm for the 30-year return level). We argue that biases and uncertainties in the atmospheric reanalyses, e.g. variability in the representation of storms, translate directly into uncertainty within the ensemble. The translation of the variability of the 99th percentile wind speeds into the sea level elevation is in the order of the variability of the ensemble spread of the modelled maximum sea levels. Our results emphasise that 13 members are insufficient and that regionally large ensembles should be created to minimise uncertainties. This should improve the ability of the models to correctly reproduce the underlying extreme value statistics and thus provide robust estimates of climate change-induced changes in the future.

Journal article(s) based on this preprint

08 Dec 2023
Uncertainties and discrepancies in the representation of recent storm surges in a non-tidal semi-enclosed basin: a hindcast ensemble for the Baltic Sea
Marvin Lorenz and Ulf Gräwe
Ocean Sci., 19, 1753–1771, https://doi.org/10.5194/os-19-1753-2023,https://doi.org/10.5194/os-19-1753-2023, 2023
Short summary

Marvin Lorenz and Ulf Gräwe

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-820', Tarmo Soomere, 17 Jun 2023
    • AC1: 'Reply on RC1', Marvin Lorenz, 14 Sep 2023
  • RC2: 'Comment on egusphere-2023-820', Anonymous Referee #2, 22 Jul 2023
    • AC2: 'Reply on RC2', Marvin Lorenz, 14 Sep 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-820', Tarmo Soomere, 17 Jun 2023
    • AC1: 'Reply on RC1', Marvin Lorenz, 14 Sep 2023
  • RC2: 'Comment on egusphere-2023-820', Anonymous Referee #2, 22 Jul 2023
    • AC2: 'Reply on RC2', Marvin Lorenz, 14 Sep 2023

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Marvin Lorenz on behalf of the Authors (14 Sep 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (15 Sep 2023) by Ilker Fer
RR by Anonymous Referee #2 (02 Oct 2023)
RR by Tarmo Soomere (07 Oct 2023)
ED: Publish subject to minor revisions (review by editor) (09 Oct 2023) by Ilker Fer
AR by Marvin Lorenz on behalf of the Authors (13 Oct 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (16 Oct 2023) by Ilker Fer
AR by Marvin Lorenz on behalf of the Authors (16 Oct 2023)

Journal article(s) based on this preprint

08 Dec 2023
Uncertainties and discrepancies in the representation of recent storm surges in a non-tidal semi-enclosed basin: a hindcast ensemble for the Baltic Sea
Marvin Lorenz and Ulf Gräwe
Ocean Sci., 19, 1753–1771, https://doi.org/10.5194/os-19-1753-2023,https://doi.org/10.5194/os-19-1753-2023, 2023
Short summary

Marvin Lorenz and Ulf Gräwe

Marvin Lorenz and Ulf Gräwe

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
We study the variability of extreme sea levels in a 13 member hind-cast ensemble for the Baltic Sea. The ensemble mean shows good agreement with observations regarding return levels and trends. Still, we still find large variability and uncertainty within the ensemble. We argue that the variability of storms in the atmospheric data directly translates into the variability of the return levels. These results highlight the need of large regional ensembles to minimise uncertainties.