Search

The northern and the eastern coast of the Adriatic Sea are occasionally affected by extreme sea-levels known to cause substantial material damage. These extremes appear due to the superposition of several ocean processes that occur at different periods, have different spatial extents, and are caused by distinct forcing mechanisms.To better understand the extremes, hourly sea-level time series from six tide-gauge stations located along the northern and the eastern Adriatic coast (Venice, Trieste, Rovinj, Bakar, Split, Dubrovnik) were collected for the period of 1956 to 2015 (1984 to 2015 for Venice) and analysed. The time series have been checked for spurious data, and then decomposed using tidal analysis and filtering procedures. The following time series were thus obtained for each station: (1) trend; (2) seasonal signal; (3) tides; (4-7) sea-level oscillations at periods: (4) longer than 100 days, (5) from 10 to 100 days, (6) from 6 hours to 10 days, and (7) shorter than 6 hours. These bands correspond, respectively, to sea-level fluctuations dominantly forced by (but not restricted to): (1) climate change and land uplift and sinking; (2) seasonal changes; (3) tidal forcing; (4); quasi-stationary atmospheric and ocean circulation and climate variability patterns; (5) planetary atmospheric waves; (6) synoptic atmospheric processes; and (7) mesoscale atmospheric processes.Positive sea-level extremes surpassing 99.95 and 99.99 percentile values, and negative sea-level extremes lower than 0.05 and 0.01 percentile values were extracted from the original time series for each station. It was shown that positive (negative) extremes are up to 50-100% higher (lower) in the northern than in the south-eastern Adriatic. Then, station-based distributions, return periods, seasonal distributions, event durations, and trends were estimated and assessed. It was shown that the northern Adriatic positive sea-level extremes are dominantly caused by synoptic atmospheric processes superimposed to positive tide (contributing jointly to ~70% of total extreme height), whereas more to the south-east, positive extremes are caused by planetary atmospheric waves, synoptic atmospheric processes, and tides (each contributing with an average of ~25%). As for the negative sea-level extremes, these are due to a combination of planetary atmospheric waves and tides: in the northern Adriatic tide provides the largest contribution (~60%) while in the south-eastern Adriatic the two processes are of similar impact (each contributing with an average of ~30%). The simultaneity of the events along the entire northern and eastern Adriatic coast was studied as well, revealing that positive extremes are strongly regional dependant, i.e. that they usually appear simultaneously only along one part of the coast, whereas negative extremes are more likely to appear along the entire coast at the same time.Finally, it is suggested that the distribution of sea-level extremes along the south-eastern Adriatic coast can be explained as a superposition of tidal forcing and prevailing atmospheric processes, whereas for the northern Adriatic, strong topographic enhancement of sea-level extremes is also important.

The dependence between extreme storm surges and wind waves is assessed statistically along the global coasts using the outputs of two numerical models consistently forced with the same atmospheric fields. We show that 55% of the world coastlines face compound storm surge wave extremes. Hence, for a given level of probability, neglecting these dependencies leads to underestimating extreme coastal water levels. Dependencies are dominant in midlatitudes and are likely underestimated in the tropics due to limited representation of tropical cyclones. Furthermore, we show that in half of the areas with dependence, the estimated probability of occurrence of coastal extreme water levels increases significantly when it is accounted for. Translated in terms of return periods, this means that along 30% of global coastlines, extreme water levels expected at most once in a century without considering dependence between storm surges and waves become a 1 in 50-year event., This study was supported by the ERA4CS INSeaPTION project (grants 690462 and PCIN‐2017‐038).

© 2014. American Geophysical Union. All Rights Reserved. Storm surges are responsible for great damage to coastal property and loss of life every year. Coastal management and adaptation practices are essential to reduce such damage. Numerical models provide a useful tool for informing these practices as they simulate sea level with high spatial resolution. Here we investigate the ability of a barotropic version of the HAMSOM model to simulate sea level extremes of meteorological origin in the Mediterranean Sea, including those caused by explosive cyclones. For this purpose, the output of the model is compared to hourly sea level observations from six tide gauge records (Valencia, Barcelona, Marseille, Civitavecchia, Trieste, and Antalya). It is found that the model underestimates the positive extremes significantly at all stations, in some cases by up to 65%. At Trieste, the model can also sometimes overestimate the extremes significantly. The differences between the model and the residuals are not constant for extremes of a given height, which limits the applicability of the numerical model for storm surge forecasting because calibration is difficult. The 50 and 10 year return levels are reasonably well captured by the model at all stations except Barcelona and Marseille, where they are underestimated by over 30%. The number of exceedances of the 99.9th and 99.95% percentiles over a period of 25 years is severely underestimated by the model at all stations. The skill of the model for predicting the timing and value of the storm surges seems to be higher for the events associated with explosive cyclones at all stations., F.M. Calafat was supported under a Marie Curie International Outgoing Fellowship (IOF) within the 7th European Community Framework Programme (grant agreement PIOFGA-2010–275851). G. Jorda acknowledges a postdoctoral grant from the Conselleria d’Educació, Cultura i Universitats del Govern de les Illes Balears, and the European Science Foundation

Bruno, M.F., Molfetta, M.G., Petrillo, A.F., 2014. The influence of interannual variability of mean sea level in the Adriatic Sea on extreme values. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13 th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 241-246, ISSN 0749-0208. The analysis of sea level data, in the low and middle Adriatic (south of Italy),collected by 6 stations belonging to the National Tide Gauge Network and to Apulia Region Meteomarine Network, shows a generalized increase in the mean sea level from 2008. The change between 2007 and 2009 is in the order of about 10 cm. A GPD distribution has been fitted to extreme series (5 extremes per year from 1999 to 2012) of sea level observed values, observed levels corrected with current annual mean sea level and tidal residuals. The analysis shows a significant increase in extremes of sea level values, while the extremes of corrected observed values and tidal residuals are quite similar respect to those found using observed data updated to 2006. Due to the sea level increase, the extremes, in observed sea level, rise drastically when updating time series to 2012, but, removing the effect of Mean Sea Level (MSL), these differences significantly decrease in the return levels.