12 Jun 2023
 | 12 Jun 2023

Bayesian extreme value analysis of extreme sea levels along the German Baltic coast using historical information

Leigh Richard MacPherson, Arne Arns, Svenja Fischer, Fernando J. Méndez, and Jürgen Jensen

Abstract. Developed coastlines require considerable investments into coastal protection measures to mitigate the effects of flooding caused by extreme sea levels (ESLs). To maximise the effectiveness of these measures, accurate estimates of the underlying hazard are needed. These estimates are typically determined by performing extreme value analysis on a sample of events taken from tide-gauge observations. However, such records are often limited in duration and the resulting estimates may be highly uncertain. Furthermore, short records make it difficult to assess whether exceptionally large events within the record are appropriate for analysis or should be disregarded as outliers. In this study, we explore how historical information can be used to address both of these issues for the case of the German Baltic coast. We apply a Bayesian Markov-chain Monte-Carlo approach to assess ESLs using both systematic tide-gauge observations and historical information at seven locations. Apart from the benefits provided by incorporating historical information in extreme value analysis, which include reduced estimate uncertainties and the reclassification of outliers into useful samples, we find that the current tide-gauge records in the region alone are insufficient for providing accurate estimates of ESLs for the planning of coastal protection. We find long-range dependence in the series of ESLs at the site of Travemünde, which suggests the presence of some long-term variability affecting events in the region. We show that ESL activity over the full period of systematic observation has been relatively low. Consequently, analyses which consider only this data are prone to underestimations.

Leigh Richard MacPherson 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 egusphere-2023-1122', Anonymous Referee #1, 10 Jul 2023
    • AC1: 'Reply on RC1', Leigh MacPherson, 05 Sep 2023
  • RC2: 'Comment on egusphere-2023-1122', Anonymous Referee #2, 11 Jul 2023
    • AC2: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
    • AC4: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
  • RC3: 'Comment on egusphere-2023-1122', Anonymous Referee #3, 17 Jul 2023
    • AC3: 'Reply on RC3', Leigh MacPherson, 05 Sep 2023

Leigh Richard MacPherson et al.

Leigh Richard MacPherson et al.


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Short summary
Efficient adaptation planning to coastal flooding caused by extreme sea levels requires accurate assessments of the underlying hazard. Tide-gauge data alone is often insufficient for providing the desired accuracy but may be supplemented with historical information. We estimate extreme sea levels along the German Baltic coast and show that relying solely on tide-gauge data leads to underestimations. Incorporating historical information leads to improved estimates with reduced uncertainties.