Can an early-warning system help minimize the impacts of coastal storms? A case study of the 2012 Halloween storm, northern Italy

摘要

The Emilia-Romagnaearly-warning system (ER-EWS) is a state-of-the-art coastal forecastingsystem that comprises a series of numerical models (COSMO, ROMS, SWAN andXBeach) to obtain a daily 3-day forecast of coastal storm hazard at eightkey sites along the Emilia-Romagna coastline (northern Italy). On the nightof 31 October 2012, a major storm event occurred that resulted inelevated water levels (equivalent to a 1-in-20- to 1-in-50-year event) andwidespread erosion and flooding. Since this storm happened just 1 monthprior to the roll-out of the ER-EWS, the forecast performance related to thisevent is unknown. The aim of this study was to therefore reanalyse the ER-EWSas if it had been operating a day before the event and determine to whatextent the forecasts may have helped reduce storm impacts. Three differentreanalysis modes were undertaken: (1) a default forecast (DF) mode based on3-day wave and water-level forecasts and default XBeach parameters; (2) ameasured offshore (MO) forecast mode using wave and water-level measurementsand default XBeach parameters; and (3) a calibrated XBeach (CX) mode usingmeasured boundary conditions and an optimized parameter set obtained throughan extensive calibration process. The results indicate that, while a "code-red"alert would have been issued for the DF mode, an underprediction of theextreme water levels of this event limited high-hazard forecasts to only twoof the eight ER-EWS sites. Forecasts based on measured offshore conditions(the MO mode) more-accurately indicate high-hazard conditions for all eightsites. Further considerable improvements are observed using an optimizedXBeach parameter set (the CX mode) compared to default parameters. A seriesof what-if scenarios at one of the sites show that artificial dunes, whichare a common management strategy along this coastline, could havehypothetically been constructed as an emergency procedure to potentiallyreduce storm impacts.