The impact of climate change on wave parameters

This study aims to investigate the impact of climate change on the wind and wave climate of the Black Sea by considering the high-emission scenario (RCP8.5) with an ensemble developed to represent the present climate. Initially, high spatial and temporal resolution climate model wind speeds containing the Black Sea were obtained from eight models (EURO-CORDEX) to achieve this goal. The third-generation wave prediction model (SWAN) with default settings was run using these winds for the historical period 1970-2005 and the future period 2006-2099. The performance analysis of the wave climate simulations was performed using ECMWF ERA5 reanalysis and altimeter satellite observations as historical period control datasets. First, the ERA5 reanalysis wave hindcasts are validated against in-situ wave measurements at different coasts of the Black Sea. Then, the normalized differences of each ensemble member against ERA5 data were computed to compare the wind and wave climates with ERA5. It was found that the mean wave parameters of the ensemble members in the Black Sea were in agreement with ERA5 in the western region. In contrast, they were overestimated by 25% on average in the eastern part. Since ERA5 significant wave heights are underestimated compared to the altimeter and in-situ measurements, the accuracy of ensemble members compared to ERA5 data was found to be reasonable, especially in the eastern region. Therefore, the ensemble model was defined with all eight ensemble members. The future simulations of this ensemble were used to show the changes in the averages of the main wave parameters (Hm0, Tm02, Pw) and wind speeds (U10). The projected changes in the mean wave and wind characteristics are determined by comparing future (2040-2069 & 2070-2099) averages relative to historical averages (1970-1999). In addition, the projected trends of significant wave height and wave energy flux (Pw) are analyzed over the future (2006-2099). U10 and Hm0 means show significant decreases up to -10% in the eastern parts of the basin. The 99th percentiles of Hm0 are projected to change more than their means and tend to increase. While the changes in the annual Pw means are similar to the changes in the Hm0 means, the seasonal changes (in the range of -15% decrease and 12% increase) are expected to be higher. Downward significant trends in the annual Hm0 means were projected with a slope of -0.08 cm/year, and downward trends in Pw were found at the level of -0.005 kWm-1/year during the future period.