Italy's CNR to use Venice as case study for Med flooding

Starting from 2019 flooding

17 May, 16:45

    NAPLES - Italy's National Research Center (CNR) will use Venice as a paradigm for Mediterranean coastal flooding, starting from extreme flooding in November 2019.

    The research will be conducted in collaboration with the University of Salerno and the University of Zagreb and will be financed through contributions from the Interreg Italia-Croatia STREAM and AdriaClim projects.

    The intensity of the November 12, 2019 flooding that hit Venice and the coasts of the Northern Adriatic is due to the overlapping of different phenomena (tides, storms, an anomalous level of the Adriatic Sea, and the rapid passing of a cyclone) that, together, made for what was only a few centimeters under the worst flooding in the history of Venice, locally called Acqua Granda.

    This unexpected, exceptional combination of factors highlighted the need to look more closely at the factors determining coastal flooding.

    The study, published in Scientific Reports, notes that the flooding was not due only to strong storms but also other processes that act on different temporal (from a few hours to several years) and spatial levels (from a few to thousands of kilometers) and can happen at the same time.

    Due to the increase of the average sea level, the tide and meteorological components carry out over the long term an ever more dominant role in determining recurrent flooding, even when not exceptional, said Christian Ferrarin from the CNR-ISMAR institute of marine sciences.

    The analysis of the historical series of sea levels also highlighted a tendency for an increase in intensity and frequency of the flooding of the past few decades. This evolution seems mainly due to long processes at the temporal level, the combination of which determines the precursor of the flooding in Venice.

    Venice is particularly appropriate for the study, Ferrarin added, given that since 1872 the sea level has been monitored and the city is frequently exposed to flooding, the frequency of which has increased over time. The city also has a system to protect against flooding that began functioning in October 2020 (MoSE) and is a case study of international relevance since it is a UNESCO protected site.

    Statistical analysis showed a significant anti-correlation between the tide caused by gravitational attraction that celestial bodies exert on the mass of water (astronomical tide) and the component due to storms, which cannot be explained by processes that occur in the coastal area.

    The most extreme events, Ferrarin said, tend to occur in conditions of medium to low tide rather than high tide. In fact, during the most extreme sea storms of 1966, 1979 and 2018, the peak of the storm happened at low tide, limiting the flooding in Venice. This issue must be looked at more closely in the future since understanding it is essential for the study of coastal flooding, also considering climate change, in which several processes could have a different evolution.

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