Reconstruction of the September 2024 extreme flood on the Lamone River in Northern Italy

Over the last twenty years, floods have represented the most predominant natural disasters occurred worldwide. Just in 2024, more than 15 European countries from Italy to Poland and from Spain to the Czech Republic experienced severe floods leading to catastrophic impacts. Between September 17 and 20, the Lamone River basin in the Emilia-Romagna Region in Northern Italy was hit by extreme precipitations and a levee-breach-induced inundation caused the flooding of urban settlements and crops near the Traversara village, an area already affected by huge floods no later than May 2023.

In the present work, the hydrological model Rhyme (River HYdrological ModEl) and the hydrodynamic model PARFLOOD are adopted to reconstruct the hydrological processes that occurred over the watershed and the dynamic of the flooding event. The spatially explicit Rhyme model enabled the description of the rainfall-runoff processes at the catchment scale by using as meteorological forcing hourly rainfall, daily cumulative potential evapotranspiration, and daily average temperatures. Due to the availability of a 16 year-series of water levels recorded at a gauging station located at the basin outlet and stage-discharge relationships, the model was calibrated from 2008 until 2024 using a Markov Chain Monte Carlo algorithm.

The flow hydrographs estimated by the hydrological model for the September 2024 event were then provided as inflow conditions to the hydrodynamic model PARFLOOD, which is a 2D parallel finite volume scheme. The breach opening on the left levee of the Lamone River was modelled by adopting a geometric approach and information about the breach characteristics (e.g. opening time and length) was provided through direct observations. The resulting flooding maps showed that after a few hours of overflowing, the levee-breach-induced flood affected the village of Traversara, urban settlements, crops, and vineyards in less than 10 hours. Moreover, the numerical results highlighted how minor channel embankments spread in the domain confined the flood propagation to the west, thus avoiding the flooding of a highly densely populated area.

Over the last two years, the Lamone River basin was affected by extreme precipitations that in many gauge stations exceeded the 500-year return period and broke historical records. Focusing on the September 2024 event, the close match between the resulting flooded areas and the observed ones, and the fair agreement between the water levels recorded at three gauge stations along the river and the resulting ones, highlighted the capability of the numerical models here adopted to support the assessment of extreme events and increase the preparedness for at-risk populations.