How to quantify long-term changes in coastal sea storminess?

• The role of storms may have been underestimated in coastal sea ecology.
• Various Estonian storm-related data sets (1899–2013) were analyzed.
• Storm manifestations (incl. surge generation, waves) are site-dependent.
• The NAO-related general cyclonic activity has shifted from autumn to winter.
• Truly extreme events do not follow decadal NAO or general storminess phases.

The paper discusses various aspects of local and regional storminess, as well as challenges in quantifying its tendencies in the eastern section of the Baltic Sea. The study is based on various long-term data sets, such as wind and sea level observation data from coastal stations and tide gauges of Estonia (1899–2013). It also discusses long-term wave hindcasts (1966–2013), reconstructions of shoreline changes, as well as the limitations and possible shortcomings in each of the data sets. Mostly located on the westerly exposed and windward coast of the semi-enclosed Baltic Sea, the case study area is sensitive to wind and storm climate changes. Different manifestations of storminess delivered somewhat specific results. When analyzed together, the first principal component of storminess was connected to the intensity of regional cyclonic activity along the polar front and had relatively high stages in 1920s–1940s, 1980s–1990s and probably also from 2010. The second component carried a local and more random imprint. Appearing independently of the high NAO or general “storminess” phases, the most notable event-driven extremes in the record were related to this component. Based on our data, we cannot confirm the existence of any general increasing long-term trends for storminess. Wherever the increase exists, it has occurred as a winter-time increase accompanied by the shift of the stormy season from autumn to winter. The spatially contrasting results for westerly and northerly exposed coasts reflect the corresponding variations in local wind, which are connected to the changes in storm track activity above northern Europe and a poleward shift of cyclones' trajectories.