Extreme waves analysis based on atmospheric patterns classification: an application along the Italian coast

The identification of homogeneous populations of data prior to perform Extreme Value Analysis (EVA) is advisable in all fields of sciences. When performing EVA on sea storms, it is also recommended to have an insight on the atmospheric processes behind the occurrence of the extremes, as this might facilitate the interpretation and ultimately use of the results. In this work, a bottom-up approach for the identification and classification of the atmospheric processes producing extreme wave conditions is revisited, and applied to several locations among the Italian buoy network. A methodology is given for classifying samples of significant wave height peaks in homogeneous subsets, and for the computation of the overall extreme values distribution starting from the distributions fitted to each single subset. From the obtained results, it is concluded that the proposed methodology is capable of identifying clearly differentiated subsets driven by homogeneous atmospheric processes, and it allows to estimate high return-period quantiles consistent with those resulting from the usual EVA. Two well-known cyclonic systems are identified as most likely responsible of the extreme conditions detected in the investigated locations. These systems are analysed in the context of the Mediterranean sea atmospheric climatology, and compared with those figured out by previous researches developed in similar frameworks.

Analysing 21st century meteorological and hydrological drought events in Slovakia

Several quite severe droughts occurred in Europe in the 21st century; three of them (2003, 2012 and 2015) hit also Slovakia. The Standardized Precipitation Index (SPI) and Standardized Precipitation and Evapotranspiration Index (SPEI) were used for assessment of meteorological drought occurrence. The research was established on discharge time series representing twelve river basins in Slovakia within the period 1981–2015. Sequent Peak Algorithm method based on fixed threshold, three parametric Weibull and generalized extreme values distribution GEV, factor and multiple regression analyses were employed to evaluate occurrence and parameters of hydrological drought in 2003, 2011–2012 and 2015, and the relationship among the water balance components. Results showed that drought parameters in evaluated river basins of Slovakia differed in respective years, most of the basins suffered more by 2003 and 2012 drought than by the 2015 one. Water balance components analysis for the entire period 1931–2016 showed that because of continuously increasing air temperature and balance evapotranspiration there is a decrease of runoff in the Slovak territory.

False-Alarm Probabilities in Period Searches: Can Extreme-Value Distributions be of Use?

Results of simulating false-alarm probabilities in irregularly sampled time series are presented. Relations to well-known expressions and earlier-used criteria are shown and tested for applicability. The use of an extreme-values distribution in this context is investigated.