How Frequent Is an Extraordinary Episode of Precipitation? Spatially-Integrated Frequency in the Júcar-Turia System (Spain)

Extreme precipitation poses a major natural hazard in the western Mediterranean, particularly along the Valencia coast, where torrential events recur with significant societal impacts. This study evaluates the feasibility and added value of an explicitly spatial approach for estimating return periods of extreme precipitation in the Júcar and Turia basins, moving beyond traditional point-based or micro-catchment analyses. Our methodology consists of progressive spatial aggregation of time series within a basin to better estimate return periods of exceeding specific catastrophic rainfall thresholds. This technique allows us to compare 10-min rainfall data of a reference station (e.g. Turis, València, 29 October 2024 catastrophe) with long-term annual maxima from 98 stations. Temporal structure is characterized using the fractal--intermittency \( n \)-index, while tail behavior is modeled using several extreme-value distributions (Gumbel, GEV, Weibull, Gamma, and Pareto) and guided by empirical errors. Results show that return periods systematically decrease and stabilize as stations are added, forming a plateau with about 15-20 stations, once the relevant spatial heterogeneity is sampled. The analysis of the precipitation in the 2024 catastrophe highlights the role of time concentration of large amounts over short effective durations. Overall, the results demonstrate that spatially-integrated return-period estimation is operational, physically consistent, and better suited for basin-scale risk assessment than purely point-based approaches.