Flood susceptibility and sediment transport analysis of Stromboli island after the 3 July 2019 paroxysmal explosion

On 3 July 2019, Stromboli volcanic island experienced a paroxysmal explosion that triggered wildfires on vegetated areas in the south, southwestern, and eastern part of the island. This study analyzes the runoff and the transport of sediment originating from rainfall, to verify whether the vegetation loss due to wildfire changed the hydrogeological structure of the affected area and the flooding hazard. A preliminary hydrological study was conducted to analyze the superficial runoff due to rainfall. According to local planning, the hydrogeological study and flood risk assessment were carried out for the return periods corresponding to 50, 100, and 300 years. The flooding levels were calculated using the hydrodynamic module of the IBER software. The IBER sediment transport module was applied in a non-stationary regime for erosion and sedimentation analysis. The results showed that the fire caused an increase of the water discharge rates between 0.06 and 0.16 m2/s, for the 50 year return period, in the Ginostra inhabited area. The great differences of the flood levels between pre- and post-eruptive scenarios, for the highest return periods, were recognized. The analysis of sediment transport showed that rains could exert an erosion and re-sedimentation effect that would transport from 0.1 m to more than 1 m of re-mobilized material in the Ginostra area, which could cause inconvenience in the inhabited area of the island.