Two recent storm-surge episodes in the adriatic

In the recent past, two intensive episodes of high sea level occurred in the Adriatic, which affected particularly the eastern coast of the basin. The events happened on 1 December 2008 and on 1 November 2012 when the eastern-coast station Bakar recorded the two highest water levels in its operational history. Interestingly, the episodes were of milder intensity in Venice, situated at the opposite coast. The question is: why these events were so pronounced along the eastern shore and was there specific meteorological background favouring stronger flooding of the eastern Adriatic coast? The study was carried out using hourly sea-level series along both sides of the basin and ECMWF reanalysis of air pressure and wind fields. Sea level was attributed to four processes: low-frequency variability, tide, pre-existing basin-wide seiche and storm-surge activity and respective contributions to high sea-level formations were evaluated. The effects of meteorological forcings over the basin were analysed by calculating along- and across-basin wind stress with respect to local bathymetry. The two marine storms were outcome of fine interplay between the four mentioned processes. During the 2008 flood, storm-surge activity was dominant while the other components reinforced the maximum. In the 2012 episode, storm surge was intensive at most stations, but relative timing of all the components was more complex. Results also revealed one common feature that was crucial for both floods being stronger along the eastern Adriatic coast. Specifically, presence of Sirocco-wind shear induced higher-than-usual water level rise along the eastern coast while transverse component of wind had a relatively small effect. This means that, at least in these two extreme episodes, transverse sea-level slope in the Adriatic was more sensitive to shear of longitudinal component of wind than to wind’s direction.