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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  29 Jun 2020

29 Jun 2020

Review status
A revised version of this preprint is currently under review for the journal NHESS.

Wave height return periods from combined measurement–model data: A Baltic Sea case study

Jan-Victor Björkqvist1, Sander Rikka2, Victor Alari2, Aarne Männik2, Laura Tuomi1, and Heidi Pettersson1 Jan-Victor Björkqvist et al.
  • 1Finnish Meteorological Institute, Marine Research, Erik Palménin aukio 1, P.O. Box 503, FI-00101 Helsinki, Finland
  • 2Tallinn University of Technology, Department of Marine Systems, Akadeemia tee 15a, 12611, Tallinn, Estonia

Abstract. This paper presents how to account for the lack of sampling variability in model data when they are combined with wave measurements. We addressed the dissimilarities between the types of data by either: i) low-pass filtering the observations or ii) adding synthetic sampling variability to the model. Measurement–model times series combined with these methods served as the basis for return period estimates of a high wave event in January 2019. During this storm northerly wind speeds in the Baltic Sea rose to 32.5 m s−1 and an unprecedented significant wave height of 8.1 m was recorded in the Bothnian Sea sub-basin. Both methods successfully consolidated the combined time series but produced slightly different results: using low-pass filtered observations gave lower estimates for the return period than using model data with added sampling variability. Extremes in both types of data followed the same type of theoretical distributions, and our best estimate for the return period was 104 years (95 % confidence 39–323 years). A similar wave event can potentially be more likely in the future climate, and this aspect was discussed qualitatively.

Jan-Victor Björkqvist et al.

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Jan-Victor Björkqvist et al.

Data sets

Measured and modelled significant wave height time series at the Bothnian Sea Wave buoy in the Baltic Sea J.-V. Björkqvist, V. Alari, L. Tuomi, and H. Pettersson

Jan-Victor Björkqvist et al.


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Latest update: 23 Oct 2020
Publications Copernicus
Short summary
Wave observations have a fundamental uncertainty due to the randomness of the sea state. Such scatter is absent in model data, and we tried two methods to best account for this difference when combining measured and modelled wave heights. The results were used to estimate how rare a 2019 storm in the Bothnian Sea was. Both methods were found to have strengths and weaknesses, but our best estimate was that, in the current climate, such a storm might on average repeat about once a century.
Wave observations have a fundamental uncertainty due to the randomness of the sea state. Such...