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Venice has long suffered the effects of rising sea levels. The last two stormy seasons brought a series of events that peaked in the great flood of November 2019. Here, we analyze that November storm, showing (1) how different factors, by themselves unexceptional, gave rise to one of the worst floods in Venice's history, and (2) that the characteristics of this event made the storm difficult to forecast accurately. We stress the need to take into account probabilistic information available from ensemble forecasts, and discuss this within the framework of Venice's present situation. At the same time, using the 2019 Venice flooding as an example that may apply to many similar coastal locations elsewhere, we look at the future, pointing out that flooding problems can only worsen in a rapidly changing natural world.

A climatology of the wind waves in the Mediterranean Sea is presented. The climate patterns, their spatio-temporal variability and change are based on a 40-year (1980–2019) wave hindcast, obtained by combining the ERA5 reanalysis wind forcing with the state-of-the-art WAVEWATCH III spectral wave model and verified against satellite altimetry. Results are presented for the typical (50th percentile) and extreme (99th percentile) significant wave height and, for the first time at the regional Mediterranean Sea scale, for the typical and extreme expected maximum individual wave height of sea states. The climate variability of wind waves is evaluated at seasonal scale by proposing and adopting a definition of seasons for the Mediterranean Sea states that is based on the satellite altimetry wave observations of stormy (winter) and calm (summer) months. The results, initially presented for the four seasons and then for winter and summer only, show the regions of the basin where largest waves occur and those with the largest temporal variability. A possible relationship with the atmospheric parameter anomalies and with teleconnection patterns (through climate indices) that motivates such variability is investigated, with results suggesting that the Scandinavian index variability is the most correlated to the Mediterranean Sea wind-wave variability, especially for typical winter sea states. Finally, a trend analysis shows that the Mediterranean Sea typical and extreme significant and maximum individual wave heights are decreasing during summer and increasing during winter.

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