The exceptional October 2024 flooding in Valencia (Spain): meteorological drivers of an extreme precipitation event

The late-October 2024 flooding in Valencia (eastern Spain) was triggered by an exceptional extreme precipitation event (EPE) associated with a quasi-stationary cut-off low over the western Mediterranean. In this study, we assess the meteorological exceptionality of the October 2024 event by combining a basin-scale, percentile-based catalogue of rainfall extremes with a multi-level diagnosis of thermodynamic and dynamical atmospheric drivers.

Extreme precipitation is analysed using the dense SAIH rain-gauge network covering the Júcar River Basin at hourly and 5-minute temporal resolution for the period 1990–2024. Hourly p99 precipitation thresholds are computed for each station using an autumn (September–November) rolling-hour climatology. Local exceedances above p99 are aggregated into a basin-wide “overall magnitude” index (M), which integrates intensity and spatial footprint. EPEs are identified as continuous periods with M > 0 and ranked according to duration, peak intensities at 1-, 3-, 6-, 12- and 24-hour accumulation periods, cumulative local magnitude, mean excess above threshold, and the number of affected stations. The October 2024 event is contextualised against (i) the seven most extreme autumn EPEs (>p99) over the last three decades and (ii) a broader set of extreme but non-record events (p90–p99).

To link hydrometeorological extremeness with atmospheric drivers, we analyse the 1–96 h period preceding peak precipitation using 3-hourly CERRA reanalysis fields from 1000 to 100 hPa. Diagnostics include integrated water vapour (IWV), vertical humidity and water vapour profiles over peak-impact areas, absolute vorticity, and wind shear across multiple pressure-layer pairs.

Results show that the October 2024 event ranks as the most extreme autumn EPE in the record, with an unprecedented cumulative local magnitude of 4392 mm, nearly twice that of the second-ranked event (2275 mm in October 2000). The event is characterised by exceptionally high IWV values (~40 mm) over the affected region and a rapid IWV increase of approximately 0.4 mm h⁻¹ (around 25 mm in less than 72 h) prior to peak intensity. In addition, very strong vertical wind shear exceeding 25 m s⁻¹ between the surface and 400 hPa favoured sustained convective organisation and quasi-stationarity. Together, these results point to a compound thermodynamic–dynamic anomaly rather than a purely moisture- or dynamics-driven extreme. The proposed framework provides a physically consistent, basin-relevant benchmark for diagnosing exceptional Mediterranean flood-producing precipitation events using high-resolution observations and reanalysis-based process indicators.