Storm surge modelling in Venice: two years of operational results

Abstract

Sea-level forecasting in Venice is a fundamental task for safeguarding the ancient city, its cultural heritage and natural environment. In the last 10 years the finite-element numerical Shallow Water Hydrodynamic Model (SHYFEM), developed at the Institute of Marine Sciences (ISMAR) of the National Research Council (CNR) of Venice, has been operationally implemented at the Istituzione Centro Previsioni e Segnalazioni Maree (ICPSM) forecast centre of the Venice Municipality. The model calculates sea level and currents in the whole Mediterranean Sea and the Venice Lagoon under the action of atmospheric forcing fields (pressure and winds) operationally supplied by the European Centre for Medium-Range Weather Forecasts (ECMWF). A neural-network module was implemented to correct model results with observed sea-level data in the Adriatic Sea. Every 6 h, the operational model produces a sea-level forecast for the next six days in the Northern Adriatic Sea in the Venice Lagoon. A statistical analysis was performed on the operational results for 2008-2009, to investigate the model goodness-of-fit and its reliability in the operational context. The main statistical quantities (mean error Ē, standard deviation σ, maximum overestimation E max and maximum underestimation E min) were computed. The model predicts the sea level both in Venice and in the open sea with good accuracy, with Ē and σ of the order of 1 cm and 5 cm, respectively, in the first 24 h of anticipation during normal weather conditions. Model errors increase when only considering periods of storm surge events.

Developing a framework for the assessment of current and future flood risk in Venice, Italy

“…Results on the effect of the MOSE barrier on the water level inside the lagoon align with previous studies, suggesting that a partial closure will still cause flooding of the old-town of Venice (Umgiesser et al, 2021). The study adds to the existing knowledge as it considers the second most extreme flood event experienced, while previous studies have mainly investigated more frequent, less extreme flood events (Zampato et al, 2016;Vergano and Nunes, 2007). The present study adds new insights suggesting that the damping effect of a partially closed MOSE barrier on the flood wave will reduce as sea level rises and may consequently amplify flood risk in future.…”

“…It is assumed that the barrier crest height increases at constant speed from the bottom of the respective inlet up to a height of 3.00 m ZMPS and closes within 30 minutes (Umgiesser et al, 2021). For the considered meteorological storm conditions, the MOSE barrier starts closing when the tidal gauge station of Punta della Salute reaches a water level of 0.65 m ZMPS (Zampato et al, 2016). This threshold is assumed to be constant for all analysed scenarios.…”

The prediction of floods in Venice: methods, models and uncertainty (review article)

“…The 12 November 2019 exceptional event was due to the combined effect of many meteorological forcings: the unusual high level of the Mediterranean Sea in November, reflecting an anomalous general atmospheric depression over the basin; a deep low-pressure system over the central-southern Tyrrhenian Sea that generated strong sirocco (southeasterly) winds along the main axis of the Adriatic Sea; a small-scale atmospheric pressure minimum developed over the northern Adriatic and moved rapidly northward along the Italian coast; and very strong winds over the Lagoon of Venice, which led to a rise in water levels and damage to the historic city (Cavaleri et al, 2020;Ferrarin et al, 2021). The peak of the meteorological contribution (100 cm) happened during the maximum of the astronomical tide with the disastrous effects of a total sea level of 189 cm.…”

“…Such underestimation was mostly due to the uncertainties related to the reproduction of the intensity and path of the small-scale cyclone traveling in the northern Adriatic Sea generating the meteotsunami along the coast and local setup within the lagoon. Ferrarin et al (2021) demonstrated that a relatively small error in the meteorological forecast (cyclone trajectory misplaced of about 10-20 km) may produce a relevant error in the sea level prediction in Venice which relies on accurate small-scale meteorological forcing.…”

“…Due to its low elevation with respect to mean sea level, for centuries the city was subject to occasional floods due to storm surge events, called Acqua alta. During the last century the frequency of flooding has steadily increased (Ferla et al, 2007;Lionello et al, 2021a) due to local land subsidence and relative sea level rise driven mainly by climate change (Carbognin et al, 2004;Zanchettin et al, 2021).…”