the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Jun 2023
Bayesian extreme value analysis of extreme sea levels along the German Baltic coast using historical information
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.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1284 KB)
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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.
- Preprint
(1284 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-1122', Anonymous Referee #1, 10 Jul 2023
The paper “Bayesian extreme value analysis of extreme sea levels along the German Baltic coast using historical information” discusses the inclusion of historic extreme events, often disregarded as outliers, into extreme value analysis and adapts an established approach to the German Baltic coast. This new methodology is able to reduce uncertainties at some of the locations of the study and to shows that current design approaches might underestimate extreme sea levels significantly due to limited availability of long tide gauge records. The paper further discusses large scale variability found in the Travemünde record, which remains undefined but might be the reason for the underestimation of extreme sea levels in other records.
The authors present their research in a precise and easy to understand manner. Their work highlights the next step in possible improvements to the coastal protection in their study area and given a well-founded recommendation on the treatment of outliers in EVA.
I therefor recommend the publication after some minor revisions, mainly focused on some clarifications and extended discussions of its important findings.
Please find further general and specific comments in tha attached pdf.
- AC1: 'Reply on RC1', Leigh MacPherson, 05 Sep 2023
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RC2: 'Comment on egusphere-2023-1122', Anonymous Referee #2, 11 Jul 2023
[General comment]
This manuscript presents the evaluation method for the extreme sea level by performing extreme value analysis using tide-gauge observations with historical information. The records of exceptionally large events, which might be excluded as outliers, are used to perform EVA. The results indicate that the extreme sea level may be underestimated in current designs and the proposed method can reduce uncertainties. This topic is interesting and the manuscript is generally well-written. Utilizing exceptionally large event data in a limited duration for evaluating extreme sea levels is very important. Therefore, the manuscript is valuable to be published after some minor revisions.
[Specific comment]
- For Fig. 1, it might be easier to understand if the place names are written on the map.
- For the size of the cycle in Fig. 2, it would be easier to understand by adding the legend of magnitude.
- The “exp” in Eqs. (3), (4), and (10) need to be modified to be normal, not italic.
- Some abbreviations, such as NHN at p. 8 in line 171 and MLE at Fig. 3, are used without explanations. Please check for missing explanations of abbreviations.
- For Line 192, how much impact does the threshold variation or the number of used historical information have on the extreme value analysis?
- In line 228, why 70 is adopted for years of the moving window?
Citation: https://doi.org/10.5194/egusphere-2023-1122-RC2 - AC2: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
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AC4: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
Sorry, we missed your last comment in our earlier reply. Regarding the moving window of 70 years:
A 70 year moving window was chosen based on the length of the high-resolution tide-gauge record, which is 71 years in length. This should be stated in the manuscript, thanks for highlighting this omission. We have added the following into Section 3.4:
“A window size of 70 years was chosen to match the length of the high-resolution tide-gauge record at Travemünde (71 years in length).”Citation: https://doi.org/10.5194/egusphere-2023-1122-AC4
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RC3: 'Comment on egusphere-2023-1122', Anonymous Referee #3, 17 Jul 2023
The manuscript by MacPherson et al. presents the importance of considering historical information, primarily related to large events, in the extreme sea level estimation. Including such data, instead of treating them as outliers, it can reduce the uncertainties to better plan for coastal adaptation. I find the article to be of very good quality, well written, with a detailed methodology and with a good discussion. However, I do recommend some improvement in the results section.
The findings presented here are not only of great interest to the coastal research community but also to coastal managers. In this sense, my overall impression is positive, and I recommend the publication. I nonetheless do have some minor comments that may help to improve the manuscript by a bit.
Please refer to the attached pdf for further specific and minor comments.- AC3: 'Reply on RC3', Leigh MacPherson, 05 Sep 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-1122', Anonymous Referee #1, 10 Jul 2023
The paper “Bayesian extreme value analysis of extreme sea levels along the German Baltic coast using historical information” discusses the inclusion of historic extreme events, often disregarded as outliers, into extreme value analysis and adapts an established approach to the German Baltic coast. This new methodology is able to reduce uncertainties at some of the locations of the study and to shows that current design approaches might underestimate extreme sea levels significantly due to limited availability of long tide gauge records. The paper further discusses large scale variability found in the Travemünde record, which remains undefined but might be the reason for the underestimation of extreme sea levels in other records.
The authors present their research in a precise and easy to understand manner. Their work highlights the next step in possible improvements to the coastal protection in their study area and given a well-founded recommendation on the treatment of outliers in EVA.
I therefor recommend the publication after some minor revisions, mainly focused on some clarifications and extended discussions of its important findings.
Please find further general and specific comments in tha attached pdf.
- AC1: 'Reply on RC1', Leigh MacPherson, 05 Sep 2023
-
RC2: 'Comment on egusphere-2023-1122', Anonymous Referee #2, 11 Jul 2023
[General comment]
This manuscript presents the evaluation method for the extreme sea level by performing extreme value analysis using tide-gauge observations with historical information. The records of exceptionally large events, which might be excluded as outliers, are used to perform EVA. The results indicate that the extreme sea level may be underestimated in current designs and the proposed method can reduce uncertainties. This topic is interesting and the manuscript is generally well-written. Utilizing exceptionally large event data in a limited duration for evaluating extreme sea levels is very important. Therefore, the manuscript is valuable to be published after some minor revisions.
[Specific comment]
- For Fig. 1, it might be easier to understand if the place names are written on the map.
- For the size of the cycle in Fig. 2, it would be easier to understand by adding the legend of magnitude.
- The “exp” in Eqs. (3), (4), and (10) need to be modified to be normal, not italic.
- Some abbreviations, such as NHN at p. 8 in line 171 and MLE at Fig. 3, are used without explanations. Please check for missing explanations of abbreviations.
- For Line 192, how much impact does the threshold variation or the number of used historical information have on the extreme value analysis?
- In line 228, why 70 is adopted for years of the moving window?
Citation: https://doi.org/10.5194/egusphere-2023-1122-RC2 - AC2: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
-
AC4: 'Reply on RC2', Leigh MacPherson, 05 Sep 2023
Sorry, we missed your last comment in our earlier reply. Regarding the moving window of 70 years:
A 70 year moving window was chosen based on the length of the high-resolution tide-gauge record, which is 71 years in length. This should be stated in the manuscript, thanks for highlighting this omission. We have added the following into Section 3.4:
“A window size of 70 years was chosen to match the length of the high-resolution tide-gauge record at Travemünde (71 years in length).”Citation: https://doi.org/10.5194/egusphere-2023-1122-AC4
-
RC3: 'Comment on egusphere-2023-1122', Anonymous Referee #3, 17 Jul 2023
The manuscript by MacPherson et al. presents the importance of considering historical information, primarily related to large events, in the extreme sea level estimation. Including such data, instead of treating them as outliers, it can reduce the uncertainties to better plan for coastal adaptation. I find the article to be of very good quality, well written, with a detailed methodology and with a good discussion. However, I do recommend some improvement in the results section.
The findings presented here are not only of great interest to the coastal research community but also to coastal managers. In this sense, my overall impression is positive, and I recommend the publication. I nonetheless do have some minor comments that may help to improve the manuscript by a bit.
Please refer to the attached pdf for further specific and minor comments.- AC3: 'Reply on RC3', Leigh MacPherson, 05 Sep 2023
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Leigh Richard MacPherson
Arne Arns
Svenja Fischer
Fernando J. Méndez
Jürgen Jensen
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1284 KB) - Metadata XML