Long-term variations of wind and wave conditions in the coastal regions of the Black Sea

Abstract

Spatial and temporal variations of significant wave height (H (m0)) and wind speed (WS) at selected locations over the Black Sea are studied based on 31-year long-term SWAN simulations forced with Climate Forecast System Reanalysis dataset. The objective was to investigate whether or not there is a possible increase in wind and wave conditions along the Black Sea shelves. Wind and wave parameters are obtained at 33 locations enclosing the Black Sea coast line from SWAN simulations and annual mean and maximum H (m0) and WS values as the climatological variables are computed for these locations. Using these data, long-term trends and their significance at these locations are investigated based on Mann-Kendall trend test. To quantify the trends, Sen's slope estimator and least square linear regression (the slope of the linear best-fit curve) are used. Variation of monthly mean H (m0) and WS values at these locations are also discussed. Besides, decadal variations of these four climatological variables at 33 locations are studied. The results show that higher wind speeds and wind wave heights are monitored in the winter season in all locations, while during the summer months, there is a significant drop in both H (m0) and WS. In the western Black Sea, average H (m0) is highest (about 1.02 m) at locations 23 and 25. During the period of 1979 and 2009, it is determined that mean WS has a weak significant increasing trend (maximum 1.29 cm/s/year) along the north-eastern coasts of Turkey and the Crimean peninsula, while there is no statistically significant H (m0) trend in the Black Sea except at location 11, offshore Sochi in the north-eastern part of the Black Sea. A weak decreasing trend (maximum 0.24 cm/year) in mean H (m0) is seen along the north-western coasts of Turkey, while maximum H (m0) and WS show no statistically significant increasing or decreasing trend except location 2, which has a weak significant increasing trend for maximum WS. All the trends at other locations for four variables are statistically insignificant, and they have no trend. The most significant difference is observed in maximum WS as 6.14 m/s in different decades in the north-western part of the Black Sea. The difference in the decades is very low in mean H (m0) at all locations. Mean wind and wave conditions at all locations have almost negligible difference, whereas decadal variations of maximum H (m0) and WS show high differences. This may be probably due to storms and cyclones conditions.