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

Abstract

Abstract. 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 three-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 one 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 three-day wave and water-level forecasts and default XBeach parameters, (2) a "perfect" offshore (PO) forecast mode using measured offshore values and default XBeach parameters; and (3) a calibrated XBeach (CX) mode using measured offshore values 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 PO 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.

Coastal aquifer response to extreme storm events in Emilia‐Romagna, Italy

“…The previous maximum value recorded by this station was 1.16 m on October 31, 2012, during another storm event (Harley et al . , ).…”

“…, ; Harley et al . , ). In this context, the objective of this study is to investigate the shallow coastal aquifer response to exceptional storm events that brought to unexperienced flooding conditions.…”

Evaluation of coastal vulnerability to flooding: comparison of two different methodologies adopted by the Emilia-Romagna region (Italy)

“…The hazard maps were qualitatively validated through the comparison with floods and damages measured after the 31 October-1 November 2012 storm (Harley et al, 2015), which was characterised by very high surge levels (1.15 m a.m.s.l., measured at Porto Corsini tide gauge, Ravenna, Fig. 1), between a 1-in-20-and a 1-in-50-year return period event and a significant wave height of 2.41 m (measured at the Cesenatico buoy, Fig.…”

“…In the Results section of the current paper, the comparison with a recent storm (10 March 2010) is presented as a validation exercise. A second validation was carried out after a strong event occurred during the night of 31 October-1 November 2012, locally known as the "Halloween storm" (Harley et al, 2015).…”

Role of Beach Morphology in Wave Overtopping Hazard Assessment

“…Studies have shown XBeach to effectively hindcast storm impact, overwash and breaching on sandy beaches [30,31]. It has also been used in the operation of coastal impact forecasting systems to forecast when storm impact hazard thresholds are exceeded by hydrodynamic and wave conditions [44,45]. As the beach at Rhyl is composed of sand and a fixed sea wall, XBeach is a suitable model to use for this study as it can represent the variable and fixed evolution of the beach and sea wall, respectively.…”