The flood frequency analysis of the catastrophic flash flood event of October 2024 in southern Valencia

Flood frequency estimates derived exclusively from local discharge records are strongly influenced by limited sample sizes and by the extrapolation of the upper tail, which can result in unrealistically discharge quantiles. The framework of the design storm paradigm is too simplistic compared with the actual spatio-temporal variability of precipitation and hydrological processes. The catastrophic October 2024 flood in southern Valencia Metropolitan Area (Spain) offers a unique opportunity to revisit flood frequency analysis under such conditions.

To address these issues, the present study integrates regional precipitation analysis, stochastic weather generation, and distributed hydrological modelling. , the proposed approach better constrains the range and frequency of rainfall-runoff conditions capable of producing extreme flows.

As a consequence, discharge magnitudes previously associated with very long return periods are shown to occur more frequently, implying lower discharge values for a given return period and a higher effective frequency of potentially damaging flows. At the same time, we found a significant difference between the return period of the precipitation of the 2024 event (above a 2,000 years), the flows generated in some tributaries (below 500 years) and that of the main inundation (around 1,000 years).