The extreme sea level event in Venice, known as Acqua Alta, is a physical phenomenon involving several compounding processes (i.e. high tides, storm surges, seiches).
Two CMCC ocean forecasting systems have been used in real time to monitor and forecast an extreme Acqua Alta event occurring in Venice on 22 November 2022.
The first system, the Copernicus Marine Service (cmems.marine.eu) Med-MFC Analysis and Forecast Physical system (MedFS), is a coupled hydrodynamic-wave modelling system implemented at around 4 km horizontal spatial resolution, which assimilates satellite also satellite and in situ observations and produces 10-days of forecasts.
The second system, the Adriatic coastal Forecasting System (AdriFS), is a higher resolution coastal ocean forecasting system, based on unstructured-grid ocean and wave modes, with spatial resolution ranging from 2km in open sea to 300m overall the coastline of the entire Adriatic Sea, including the Venice lagoon an its connections with the open sea. The operational chain is based on a downscaling approach from MedFS and produces 3-days of forecasts.
Both systems include the explicit representation of tides and are forced by the high-resolution ECMWF-IFS (European Centre for Medium-Range Weather Forecasts – Integrated Forecasting System) atmospheric fields at around 10 km resolution (with 1 hour temporal frequency for the first 3 days of forecast).
The CMCC ocean forecasting systems already demonstrated their predictive capacity in the past, providing crucial information to alert for intense storm events, such as the Venice Acqua Alta on 12 November 2019 and the surge induced by Ianos Medicane.
For the forecast of the severe event of 22 November 2022, both MedFS and AdriFS were able to predict the extreme peak of sea level three/four days in advance. In particular, the highest sea level for the MedFs and AdriFs systems is predicted to be 161 cm and 155cm (Figure 1), respectively, on 22nd of November around 8:30 UTC (9:30 local time). MedFS model analyses are also compared with the ISPRA Tide Gauge sea level measurements in the days before the event (Figure 1 left panel) showing good accuracy of the model.
The forecasting products delivered on the day before the event (21st November) shows for both systems the highest sea level of 162 cm (Figure 2, top panels) around 8:30 UTC, also in close agreement with the forecast delivered the Comune di Venezia Centro Previsione Segnalazione Maree of 160 cm (Figure 2, bottom panel).
This forecasting study underlines the capacity of predicting the extreme event several days in advance, which is recognized to be an important support for decision makers to manage storm surge induced risks.
