Linking rainfall spatial organization and distributed travel times to critical flood-contributing areas in a mountainous urban catchment

Abstract. Extreme rainfall events can produce different flood responses depending on how rainfall is organized across a catchment and how this organization interacts with the drainage system. This study examines the spatial and temporal characteristics of four high-magnitude rainfall events and their associated flood responses in the Medellín River–Aula Ambiental catchment in the Valle de Aburrá, Colombia. The analysis combines weather radar observations, measurements from a dense network of rain gauges, and high-frequency river level and discharge records. The events were characterized according to rainfall magnitude, spatial distribution, temporal evolution, displacement, and location within the catchment. These characteristics were then examined in relation to rainfall distribution across areas with contrasting degrees of urbanization and to the timing of rainfall relative to the observed river response.

The results indicate that the spatial organization and movement of rainfall can play an important role in shaping the magnitude and timing of the hydrological response. Events with rainfall concentrated along the drainage network or over highly urbanized areas produced a more spatially synchronized contribution to the river response, whereas rainfall occurring in less urbanized or less hydraulically connected parts of the catchment contributed differently to the observed response. The analysis also shows that the area contributing to the flood peak can vary substantially among events, highlighting the dynamic nature of rainfall–catchment interactions.

The findings suggest that rainfall accumulation alone may not fully describe the potential hydrological response of a high-magnitude event. The location, movement, and spatial organization of rainfall provide additional information for interpreting flood response in urbanizing catchments. Future research could investigate these relationships using larger event samples and synthetic rainfall generation, while incorporating distributed travel times and a wider range of rainfall spatial configurations to further examine their implications for flood response.