Emerging changes in sub-daily precipitation extremes in Catalonia (1996-2025)

Sub-daily precipitation plays a key role in Mediterranean hydrometeorological hazards, where short-lived, high-intensity events are the main drivers of flash flooding. This study analyses observed changes in hourly precipitation patterns across the Internal Basins of Catalonia (NE Iberian Peninsula) over the period 1996–2025, using a dense network of automatic rain gauges from the Meteorological Service of Catalonia. Data quality was ensured through a combination of operational quality control and advanced automated procedures developed within the INTENSE project, allowing for a robust characterization of extreme events.

The results reveal a consistent intensification of short-duration precipitation extremes. Significant positive trends are detected in maximum precipitation over 1-hour and multi-hour aggregations (3h, 6h), as well as in the frequency of high-intensity episodes exceeding fixed thresholds (e.g. 30 mm in 1 hour). In parallel, a tendency toward shorter event durations is observed, indicating a shift toward more temporally concentrated rainfall. These changes are particularly pronounced in coastal and southern sectors, suggesting an increasing dominance of convective processes.

Despite the strengthening of sub-daily extremes, no clear corresponding increase is found in longer-duration accumulations (24h), pointing to a redistribution of rainfall toward more intermittent and intense bursts. Complementary daily-scale analysis (1950–2024) indicates a general decline in total precipitation and in the frequency of rainy days, reinforcing the interpretation of a more irregular precipitation regime.

Overall, the results highlight a marked transition toward fewer but more intense and short-lived precipitation events. This evolution has significant implications for flood risk, urban drainage performance, and water management in Mediterranean catchments under ongoing climate change.