Occurrence of flash floods in the karst environment of Apulia (Southern Italy)

Floods in karst environment are among the most frequent and damaging geological hazards, due to hydraulic and hydrogeological peculiarities of the karst terrains. Since absence of water at the surface is one of the main features characterizing karst, the occurrence of floods in consequence of prolonged rainfall, or of concentrated and intense rainstorms, may often result in severe damage to human activities and infrastructures, threatening lives as well. Apulia, the south-eastern sector of Italy, almost entirely consisting of soluble rocks intensely affected by karst processes, is not an exception at this regard. Flash floods have repeatedly characterized the history of many Apulian towns, and the number of events, with consequences on the society, has increased in the last decades, due to expansion of the urbanized and industrial areas. This was often carried out without considering the peculiarity of karst, and the possibility of occurrence of flash floods. Therefore, the effects have often been devastating, in terms of both casualties and economic losses. Through description of a series of events, that have hit different sectors of the region, this article presents a documented chronology of the events occurred in Apulia, in the attempt to contribute to build a deeper knowledge about the areas inundated by floods, their triggering conditions, and the relationships with human activities. The Apulian sectors that will be dealt with are: the Gargano Promontory, where, at the beginning of September 2014, severe rainstorms caused many types of geohazards, including floods, and claimed some casualties; the town of Bisceglie, north of Bari, where the system of temporary water courses (locally named lame) work as the main water flow way during floods; the sector comprising Putignano and CastellanaGrotte, in the Low Murge, where an high number of swallow holes had been closed in recent decades; the coastal area downhill from Ostuni, where several tourist resorts are located; the town of Ginosa, where two different flood events in 2013 sadly resulted in 4 victims; and the Salento peninsula, where many urban centers are interested by floods and inundations, even in consequence of not significant rainfall events. In addition, to analyse the pluviometric events causing the floods, the role of the geological and morphological features in karst will be examined, also as regards the transport of solid materials by the flowing water, that may significantly contribute to the registered damage.