Ensemble approach for projections of return periods of extreme water levels in Estonian waters

Spatial variability in the trends in extreme storm surges and weekly-scale high water levels in the eastern Baltic Sea

“…A certain discrepancy between modelled and observed storm surges has been found in the western Baltic Sea (Meier et al, 2004). As the modelled statistics of extremes has very good match with similar statistics of measured water level data for most of the Estonian coast, a possible reason for this mismatch may be the ignoring of wave-induced set-up in the RCO model (Eelsalu et al, 2014).…”

“…These data sets have been extensively described and analysed from various viewpoints, e.g., the overall course and periodic components of the water level (Raudsepp et al, 1999), projections of extreme water levels and their return periods (Suursaar and Sooäär, 2007), the feasibility of ensemble approach for projections of water level extremes (Eelsalu et al, 2014) or the separation of the total water level into short-term and weekly-scale components . The gauge at Tallinn Harbour seems to most adequately represent the offshore water level (Eelsalu et al, 2014) and the data from this site is chosen to illustrate our approach.…”

“…The existing network of tidal gauges is not perfect even in the most densely covered areas such as the North Sea (Arns et al, 2015) or the Baltic Sea (Hünicke et al, 2015). Moreover, the records of some gauges may contain extensive distortions (e.g., by local wave set-up, Eelsalu et al, 2014) and do not always provide an adequate quantification of the spatial extent of single surges (Brakenridge et al, 2013). For this reason we largely rely on numerically simulated water levels.…”

Separation of the Baltic Sea water level into daily and multi-weekly components

“…Generally the model represents well both the time series and statistics of water levels but shows a certain mismatch for storm surges in the western Baltic Sea (Meier et al, 2004). A possible reason for the mismatches may be the ignoring of wave-induced set-up (Eelsalu et al, 2014).…”

“…A specific problem in the analysis and forecast of water levels in the eastern Baltic Sea is the frequent presence of outliers in water level records, which may substantially modify the projections of future extreme water levels and associated return periods (Suursaar and Sooäär, 2007;Eelsalu et al, 2014). The proposed separation sheds some light on this problem by showing from where the outliers stem.…”