Temporal Variability of the Wind Wave Parameters in the Baltic Sea in 1979-2018 Based on the Numerical Modeling Results

Purpose. The aim of the paper is to identify possible trends in the wave climate dynamics in the Baltic Sea, and to analyze statistical significance of the coefficients of these trends based on the results of their numerical modeling for 1979-2018. Methods and Results. The simulations for 1979-2018 (40 years) were carried out on an irregular grid using the MIKE 21 SW spectral wave model. The wind forcing was preset according to the ERA-Interim reanalysis data. The model was calibrated and validated against the data of wave buoys located in the northern and southern parts of the Baltic Sea. Based on the calibrated model, the wind wave parameters were calculated for the whole Baltic Sea area from 1979 to 2018 with the interval 1 hour. These parameters became the initial data for estimating temporal variability of the wind wave heights in the Baltic Sea for 40 years. The simulation results obtained on the irregular grid were interpolated to the regular one. It permitted to construct the maps of distribution of the maximum and average (for the 40-year period) significant wave heights in the Baltic Sea. The time trends for the average annual significant wave height values were revealed, and statistical significance of the coefficients of these trends was estimated. Conclusions. The average annual values of the significant wave heights over almost the whole Baltic Sea area for 1979-2018 (40 years) tend to decrease with the rate not exceeding 2-3 cm (similar to 2-3 %) per 10 years. The highest rate reduction is observed in the southeastern part of the Baltic Sea, the lowest - in the Gulf of Bothnia and the Gulf of Finland. Interannual variability of the average annual significant wave heights and the changes along the trend during the entire 40-years period are of the same order.