Black Sea extreme wave events

'''DEFINITION'''

Extreme wave characteristics were derived by analysing and counting individual storm events and their long-term means and trends based on the Black Sea wave model reanalysis (product BLKSEA_MULTIYEAR_WAV_007_006). Storms were identified using the Weisse & Günther (2007) method. The basis of the method is the definition of a severe event threshold (SET), which we define as the 99th percentile of the significant wave height (SWH). Events are counted when SWH exceeds and then drops below the SET at any grid point. Three additional key parameters - event lifetime (duration of SET exceedance), intensity (maximum SWH minus SET), and maximum event area (geographic extent of SET exceedance) - were calculated but are not included in this OMI. Annual averages of event number, lifetime, and intensity were computed to determine long-term means. This OMI comprises the annual mean event number, the anomaly for the most recent year in the multi-year dataset, and the linear trend of the annual event number as presented in Staneva et al. (2022). All qualifying events, regardless of location within the domain, contributed to the statistics, based on data from 1950 to -18M.

'''CONTEXT'''

In the last decade, the European seas have been hit by severe storms, causing serious damage to offshore infrastructure and coastal zones and drawing public attention to the importance of having reliable and comprehensive wave forecasts/hindcasts, especially during extreme events. In addition, human activities such as the offshore wind power industry, the oil industry, and coastal recreation regularly require climate and operational information on maximum wave height at a high resolution in space and time. Thus, there is a broad consensus that a high-quality wave climatology and predictions and a deep understanding of extreme waves caused by storms could substantially contribute to coastal risk management and protection measures, thereby preventing or minimising human and material damage and losses. In this respect and in the frame of climate change, which also affects regional wind patterns and therewith the wave climate, it is important for coastal regions to gain insights into wave extreme characteristics and the related trends. These insights are crucial to initiate necessary abatement strategies especially in combination with extreme wave power statistics (see OMI OMI_EXTREME_WAVE_BLKSEA_wave_power) and has already successfully been applied to different regions such as the North Sea (Weisse and Günther, 2007), Black Sea (Staneva et al., 2022), and South Atlantic (Gramcianinov et al., 2023a and 2023b).

'''CMEMS KEY FINDINGS'''

The yearly mean number of storm events is rather low in regions where the average annual lifetime and intensity of storms are high. In contrast, the number of events is high where their lifetime and intensity are low. While the southwest Black Sea is exposed to yearly mean storm event numbers of below the long-term spatial averages (7.3 events), it is observed that the yearly mean lifetime of the events in the same region is higher than the long-term averages. The extreme wave statistics based on the 99th percentile threshold of the significant wave height (SWH) are very similar to the wind sea wave parameter, and the swell contribution is much lower. On overall, the yearly trend of the storm events is slightly negative (-0.01 events/year) with two areas showing positive trends located in the very east and west. In terms of the mean number of storm events in 2023, the event numbers exceed the average numbers almost everywhere in the domain (+1.8 events on spatial average) indicating a relatively stormy year 2023.

'''DOI (product):''' https://doi.org/10.48670/mds-00348