The October 2024 Extreme Precipitation Event over Valencia: Storyline Attribution of the Synoptic-Scale Thermodynamic Drivers

Abstract. In late October 2024, the western Mediterranean (WMed) region experienced an extreme precipitation event (EPE) centred over Valencia, southeastern Spain, associated with a quasi-stationary cut-off low (COL), producing record rainfall, flash floods, and severe societal impacts. The COL generated an atmospheric-river-like moisture plume from northwestern Africa, while additional moisture originated from the warm Mediterranean Sea. Interaction with regional orography created a highly unstable environment, favouring deep convection and intense local rainfall. To assess the influence of anthropogenic climate change, we analyse high-resolution (∼9 km) storyline simulations from the European Union’s Destination Earth initiative, using the coupled IFS-FESOM model spectrally nudged with ERA5. Two climate scenarios are compared: Factual (present-day) and Counterfactual (~1950), isolating thermodynamic responses while keeping large-scale circulation fixed. Long-term IFS-FESOM and ERA5 datasets provide a climatological reference for event extremeness. Results show that the synoptic configuration alone was sufficient to produce extreme rainfall, but human-induced warming substantially enhanced its magnitude. Moisture content and transport increased by 18–24 %, convective instability (CAPE) by ~25 %, and precipitation over Valencia increased by ~20 % in the Factual scenario. Sea surface temperatures in the Western Mediterranean were ~2 °C warmer, amplifying evaporation. Peak precipitation rates exhibited nonlinear amplification, on 29 October were about 36 % higher in the Factual scenario, exceeding the Clausius–Clapeyron (CC) scaling expected from the mean warming between scenarios. These findings indicate that anthropogenic warming can intensify EPEs in the WMed even when synoptic drivers alone would generate extreme rainfall, highlighting thermodynamic amplification as a key mechanism in Mediterranean flood events. High-resolution, physically consistent storyline simulations offer a robust framework for event-based attribution and improve understanding of future climate risks in vulnerable coastal regions.