The 2017 Flash Flood of Livorno (Italy): Lessons Learnt from an Exceptional Hydrologic Event

Between 9th and 10th September 2017 a catastrophic, very intense rainfall event struck the city of Livorno in the Tyrrenian coast of central Italy causing eight fatalities. The event was characterized by very high rainfall intensity (>100 mm h(-1)) that persisted on a small portion of territory causing huge rainfall accumulations (>260 mm). The aim of the work is to reconstruct the flash flood to understand how much the event was exceptional under the hydrologic and impact aspects. The rainfall event and the inundation have been reconstructed by analyzing the rain gauge data of the regional hydrologic service. The discharges have been simulated using MOBIDIC, a continuous distributed hydrologic model already operational in the region for hydrologic predictions. The exposure and damages to buildings have been analyzed and compared with the official claims. The results show that the flash flood was exceptional since most of the river reaches in the area have overcome of about 50% the 200 years return period discharge, used to design the flood defenses according to the national regulations.