Hydrosedimentary dynamics and sediment source activation during a prolonged extreme rainfall event in a Mediterranean catchment

This study analyses the response of a Mediterranean agroforestry catchment to Storm Juliette, an episode of prolonged rainfall (208 mm in 5 days). Hydrological monitoring combined with sediment fingerprinting using colour tracers and a Bayesian mixing model was applied to assess sediment dynamics. The results show a peak discharge of 2.4 m 3 ·s -1 and a sediment yield of 3.9 t·km -2 , markedly higher than the 2012–2018 average (0.8 m 3 ·s -1 ; 0.7 t·km -2 ). Channel banks and cropland were identified as the main sediment sources during the event, in line with long-term observations suggesting a dominant role of the most functionally connected catchment compartments. Although this less frequent, high-magnitude event markedly increased the effective catchment area and overall sediment mobilisation, sediment contributions remained strongly conditioned by the spatial organisation of buffers, barriers and source areas within the catchment. The analysis of such infrequent events provides critical insight for improving soil and water management strategies in highly anthropized Mediterranean catchments under increasing climate variability.