Reconstruction of the October 2024 catastrophic flooding in the southern Valencia Metropolitan Area, Spain

On 29 October 2024, an exceptional hydro-meteorological event impacted eastern Spain, producing extreme rainfall accumulations and widespread flash flooding, with the most severe consequences recorded in the Valencian Community. The event resulted in 238 fatalities nationwide, of which 230 occurred in the province of Valencia, and caused economic losses estimated at approximately €17 billion. More than 80% of the fatalities were concentrated in the southern Valencian Metropolitan Area, highlighting its extreme vulnerability to compound rainfall-runoff processes. This area is a highly urbanized Mediterranean lowland located south of the city of Valencia (Spain), draining an area of approximately 530 km² through a dense network of ephemeral streams. These catchments are characterized by short response times, steep upstream slopes, permeable lithologies, and limited natural floodplain storage. Downstream of natural flood-lamination areas such as the Pla de Quart, river channels intersect densely populated municipalities, where urban expansion has progressively encroached upon flood-prone areas, substantially increasing exposure and, consequently, flood risk.

This contribution presents a detailed reconstruction of this catastrophic flooding, integrating meteorological analysis, distributed hydrological modelling, and high-resolution hydraulic simulations. Rainfall reconstruction was performed using an extensive rain-gauge network across the Valencian Community, capturing the strong spatial variability and temporal clustering of the event. The storm evolved through two clearly differentiated phases: an initial morning rainfall episode that led to widespread soil saturation across the catchments, followed by an afternoon-evening phase characterized by extraordinary rainfall intensities and persistence.

Hydrological and sediment transport simulations were conducted to represent both the generation and propagation of runoff and solid load throughout the catchment, using the fully distributed eco-hydrological model TETIS. The modelling framework combined long-term daily simulations to establish realistic antecedent conditions with event-scale subdaily simulations at 10-minute resolution. This approach enabled the reconstruction of hydrographs and sediment fluxes for the main tributaries upstream of flood-lamination zones, prior to the occurrence of major overbank flooding. It also allowed the estimation of peak discharges that largely exceeded the instrumental record, highlighting the significant contribution of solid load to the total flood volume.

The resulting hydrographs (with a combined peak of 7,500 m³/s) were used as boundary conditions for two-dimensional hydraulic modelling, allowing the reproduction of flood propagation and inundation patterns in highly urbanized areas of southern Valencian Metropolitan Area. Results show that flood depths and impacts were strongly amplified by floodplain anthropization associated with urban expansion, leading to water levels substantially higher than those expected under more natural conditions.

This integrated reconstruction improves the understanding of the coupled meteorological and hydrological processes that controlled the October 2024 flood and provides a physically consistent basis for assessing flood hazards in highly urbanized Mediterranean catchments.