| 20 Nov 2025
An ensemble of regional wind wave scenarios for the North Sea and the Baltic Sea: a revisit
Abstract. Storms and associated marine hazards pose a environmental risks, particularly under long-term changes driven by anthropogenic climate change. This study assesses the potential impacts of future climate change on annual median and extreme wave conditions in the North Sea and the Baltic Sea using a ensemble of up to 14 and 8 regional projections, respectively. The ensemble includes simulations based on IPCC CMIP3 and CMIP5 scenarios, incorporating a range of global and regional climate models, initial conditions, and emission scenarios to reflect diverse sources of uncertainty. High- and low-emission sub-ensembles were used to evaluate the influence of emission scenarios on projected wave climate changes towards the end of the 21st century. Despite variations in magnitude and spatial patterns across the ensemble, some robust spatial and temporal trends emerge.
A meridional gradient of changes is simulated in the North Sea. Significant wave heights decrease along the western margins and increase in the east. These changes are more pronounced under high-emission scenarios, with median values decreasing by up to 5 % in the west and annual maxima increasing by over 5 % in the east. Time series analysis confirms these trends at selected locations, although there is still considerable internal variability among ensemble members.
In the Baltic Sea, both median and extreme wave heights are simulated to increase by more than 5 % in some areas. Although the response to emission scenarios is less distinct than in the North Sea, high-emission scenarios still yield more pronounced increases. Temporal analysis reveals that simulated changes become statistically significant by mid-century in central areas and later in western regions.
The results indicate a robust increase in wave height in the eastern North Sea and many regions of the Baltic Sea, as well as a consistent decrease in the western North Sea, particularly under high-emission scenarios. However, these trends are superimposed on substantial temporal and internal variability, highlighting the importance of using ensemble-based assessments to evaluate future marine climate conditions.
1. General comments:
- Concise review of regional wind wave scenarios in the North and Baltic Sea areas, focusing on the range of potential future changes.
- Uses state-of-the-art analysis methods, e.g. the ensemble approach and statistical significance tests.
- Analysis and results for average and higher wave events, considering spatial and temporal variability.
- Discusses the role of uncertainty in future projections.
The scientific methods and assumptions are clearly outlined, and the experiments and calculations are well described. It would be helpful to mention the sources of the regional climate model data, e.g. where the data was provided/downloaded from. This would facilitate reproduction by fellow scientists.
The author gives proper credit to related work in the field and indicates new contributions (see general comments).
The title accurately reflects the contents of the paper (see specific comments).
The abstract provides a concise and complete summary of the paper.
The overall presentation is well structured and clear, and the language is fluent and mostly correct (see technical corrections).
Abbreviations and units are used correctly.
Some minor aspects of the paper could be improved (see the specific comments).
The number and quality of references are appropriate.
The supplementary materials provided are appropriate.
2. Specific comments:
The changes in significant wave height are analysed and discussed. Changes in wave periods and directions are not analysed or discussed, even though these can also have important implications, e.g. for coastal erosion and flooding.
The limitation of the study to significant wave height should be clearer outlined, e.g. in the title or introduction.
The authors show that patterns of change may diverge depending on the statistical variable under consideration. The implications of climate change signals could be discussed in the 'Discussion' section. For example, a relative change in the ensemble median or the 99th percentile, or the maximum and with the same magnitude can have different implications.
3. Technical corrections:
L134: Replace the plural 'areas' with the singular.
L279: the word 'is' is missing before 'evident'.