The Emilia-Romagna early-warning system (ER-EWS) is a state-of-the-art coastal forecasting system that comprises a series of numerical models (COSMO, ROMS, SWAN and XBeach) to obtain a daily 3-day forecast of coastal storm hazard at eight key sites along the Emilia-Romagna coastline (northern Italy). On the night of 31 October 2012, a major storm event occurred that resulted in elevated water levels (equivalent to a 1-in-20- to 1-in-50-year event) and widespread erosion and flooding. Since this storm happened just 1 month prior to the roll-out of the ER-EWS, the forecast performance related to this event is unknown. The aim of this study was to therefore reanalyse the ER-EWS as if it had been operating a day before the event and determine to what extent the forecasts may have helped reduce storm impacts. Three different reanalysis modes were undertaken: (1) a default forecast (DF) mode based on 3-day wave and water-level forecasts and default XBeach parameters; (2) a measured offshore (MO) forecast mode using wave and water-level measurements and default XBeach parameters; and (3) a calibrated XBeach (CX) mode using measured boundary conditions and an optimized parameter set obtained through an extensive calibration process. The results indicate that, while a "code-red" alert would have been issued for the DF mode, an underprediction of the extreme water levels of this event limited high-hazard forecasts to only two of the eight ER-EWS sites. Forecasts based on measured offshore conditions (the MO mode) more-accurately indicate high-hazard conditions for all eight sites. Further considerable improvements are observed using an optimized XBeach parameter set (the CX mode) compared to default parameters. A series of what-if scenarios at one of the sites show that artificial dunes, which are a common management strategy along this coastline, could have hypothetically been constructed as an emergency procedure to potentially reduce storm impacts.

This paper reviews the state of the art in storm surge forecasting and its particular application in the northern Adriatic Sea. The city of Venice already depends on operational storm surge forecasting systems to warn the population and economy of imminent flood threats, as well as help to protect the extensive cultural heritage. This will be more important in the future, with the new mobile barriers called MOSE (MOdulo Sperimentale Elettromeccanico, Experimental Electromechanical Module) that will be completed by 2021. The barriers will depend on accurate storm surge forecasting to control their operation. In this paper, the physics behind the flooding of Venice is discussed, and the state of the art of storm surge forecasting in Europe is reviewed. The challenges for the surge forecasting systems are analyzed, especially in view of uncertainty. This includes consideration of selected historic extreme events that were particularly difficult to forecast. Four potential improvements are identified: (1) improve meteorological forecasts, (2) develop ensemble forecasting, (3) assimilation of water level measurements and (4) develop a multimodel approach.

Addressing coastal risks related to sea storms requires an integrative approach which combines monitoring stations, forecasting models, early warning systems, and coastal management and planning. Such great effort is sometimes possible only through transnational cooperation, which becomes thus vital to face, effectively and promptly, the marine events which are responsible for damage impacting the environment and citizens' life. Here we present a shared and interoperable system to allow a better exchange of and elaboration on information related to sea storms among countries. The proposed integrated web system (IWS) is a combination of a common data system for sharing ocean observations and forecasts, a multi-model ensemble system, a geoportal, and interactive geo-visualisation tools to make results available to the general public. The multi-model ensemble mean and spread for sea level height and wave characteristics are used to describe three different sea condition scenarios. The IWS is designed to provide sea state information required for issuing coastal risk alerts over the analysed region as well as for being easily integrated into existing local early warning systems. This study describes the application of the developed system to the exceptional storm event of 29 October 2018 that caused severe flooding and damage to coastal infrastructure in the Adriatic Sea. The forecasted ensemble products were successfully compared with in situ observations. The hazards estimated by integrating IWS results in existing early warning systems were confirmed by documented storm impacts along the coast of Slovenia, Emilia-Romagna and the city of Venice. For the investigated event, the most severe simulated scenario results provide a realistic and conservative estimation of the peak storm conditions to be used in coastal risk management.

A hierarchy of medium (2 km) and high (0.5 km) resolution operational models cast in the Adriatic sea (NE Mediterranean Sea), relying on an updated core w.r.t. previously existing one, characterized by having a wide variety of applications ranging from civil protection to scientific ones, is presented and described. The computing core of the system sits at Hydro-Meteo-Clima Service (SIMC, Bologna), and the scientific supervision is provided by DISVA Polytechnic University of Marche and CNR-ISMAR Venice. The core of the operational system is based on the Regional Ocean Modeling System, version 3.4. The hydrodynamic variables (e.g. sea surface elevation, currents, temperature, salinity, storm surge height), and wave parameters are predicted every day for the next 72 hours. The surface forcing for the hydrodynamic (AdriaROMS 4.0) and wave (SWAN) operational models is derived from the predicted results of the operational meteorological model COSMO-I7 (7 km resolution) which forecasts atmospheric fields over the whole Italian seas. Hydrodynamic results are verified against oceanographic and wave buoys, tide gauges, bottom mounted acoustic current meter profilers, available in the coastal waters of the Adriatic Sea and oceanographic surveys. More specifically, CNR-ISMAR in the northern Adriatic Sea manages a meteo-oceanographic buoy network and the fixed ocean observatory tower “Acqua Alta”, SIMC manages a wave buoy. Aiming to obtain forecast improvements in coastal areas of northern Adriatic Sea, a newly implemented, more resolved (0.5 km) ROMS version two-way coupled with SWAN is nested in the operational AdriaROMS 4.0 covering the Adriatic Sea at 2 km horizontal resolution. Outputs of operational models drive dedicated submodels for oil-spill transport and dispersion, coastal morphodymanic, sediment transport, saline wedge, water quality.