An updated "climatology" of tornadoes and waterspouts in Italy

Ten years of tornadoes (TR) and waterspouts (WS) in Italy are analysed in terms of geographical, seasonal, monthly, diurnal, and rating distribution. Starting from the European severe weather database, a comprehensive data set is developed for the period 2007–2016, which includes 707 WS and 371 TR. The category of WS includes many weak events but also some intense vortices, able to produce significant damages as they make landfall. WS develop mainly near the Italian coasts exposed to westerly flows (Tyrrhenian and Apulia region Ionian coast); 25% of them makes landfall and becomes TR. The majority of WS develops in autumn (43%), followed by summer (33%). The average density is 0.9 events per 100 km of coastline per year, although there is a strong subregional variation, with peaks of around 5 in some spots along the Tyrrhenian coast. TR originate from WS in about half of cases; the average density of TR is 1.23 events per 104 km2 per year, which is comparable with other Mediterranean regions. The occurrence of TR is more frequent in summer, followed by autumn; however, limiting the analysis to TR originated inland, the number of events is maximum in summer and late spring. The latter result suggests a distinction of “continental” cases, mainly affecting northern Italy in late spring and summer, and “maritime” cases, which affect mainly the peninsular regions in late summer and autumn. The highest density of TR was reported along the coasts of Lazio and Tuscany, in the Venetian plain, in the southern part of Apulia: in these regions, the density of events is comparable with that of the U.S. states with the highest TR rates. In contrast, the probability of significant TR in any Italian region is much smaller than that of the U.S. states with the highest risk.