Reconstruction of the October 2024 flood in l’Horta Sud (Valencia, Spain)

Study region l'Horta Sud (Valencian Community), eastern Spain, the area most severely affected by the 29 October 2024 flash-flood event. Study focus An exceptional hydro-meteorological event produced extreme rainfall and widespread flash flooding across eastern Spain, with more than 80% of the 239 fatalities occurring in l′Horta Sud. This study presents an integrated reconstruction of the event by combining high-resolution precipitation analysis, distributed hydrological and sediment transport modelling, and two-dimensional hydraulic simulations. Rainfall fields were reconstructed from a dense rain-gauge network at daily and 10-minute resolutions to characterize the spatial and temporal evolution of the storm. Simulated hydrographs were subsequently used as boundary conditions for hydraulic modelling to reconstruct flood propagation and inundation patterns. New hydrological insights for the region Hydrological simulations reveal a highly synchronized basin response, with the combined tributary contributions corresponding to an equivalent upstream inflow on the order of 7,000 m³ /s prior to significant floodplain storage, illustrating the exceptional magnitude of the event and exceeding peak discharges documented in Spanish instrumental records. Sediment transport represented approximately 7% of the total flood volume. The agreement between simulated discharges, sediment dynamics, and observed inundation extents supports the physical consistency of the reconstruction. The results demonstrate the value of integrated, event-based analyses for improving the understanding and assessment of extreme Mediterranean flash floods.