Decadal changes in the Baltic Sea wave heights

The analysis of decadal changes to the average and extreme wave properties in the Baltic Sea is performed based on the wave hindcast for the entire Baltic Sea 1970-2007 using the wave model WAM and adjusted geostrophic winds under the assumption of no ice cover. The overall wave activity in the entire basin has limited variations over the 38 years of simulations. The local wave properties reveal strong decadal-scale signal in many parts of this water body. Its amplitude is up to 15% of the long-term average value of the significant wave height. The typical time interval between episodes of high or low annual average significant wave height is 10-12 years. The analogous interval between episodes of high and low 99%-iles of wave heights is about 5 years. Changes to the wave properties in different sea areas may be completely different in different decades. The overall maximum in the simulated annual mean significant wave height has drifted from an area between Gotland and Öland in the 1970s to the northern Baltic Proper at the turn of the millennium.