Flash floods risk variation of steep drainage basins in Calabria (Italy) and the role of rainfall and anthropogenic modifications since 1800

Abstract

In the present work, for a study area located in the southernmost province of continental Italy, data concerning the historical series of floods which have occurred since XVII century have been collected. Damages caused by flood events were discussed together with rainfall regime and trend (for the period in which data are available) and with main modifications due to variations in population number. The aim was to assess if the frequency of damaging floods is changing and if there is a role of rainfall and/or of anthropic modifications of land use on these changes. 150 damaging floods were analysed; 4% of the total were floods which caused damages to people, and which mainly occurred in the past centuries. Notwithstanding, the trend of damaging floods is increasing due to the effects of floods observed in the last decades. At the same time, the rainfall trend is generally decreasing, as observed at regional scale, and not significant to justify the flood recurrence increase. The population trend is characterised by a huge increase observed in the last decades. On this basis, the progressive urban enlargement, realised careless of both drainage network characteristics and extreme floods, can be considered as the main source of increasing risks due to damaging floods.