HYDROLOGICAL DROUGHT-TO-FLOOD TRANSITIONS ACROSS BRAZILIAN CATCHMENTS

Código

V-END_II-EBHE0049

Autores

Abderraman Róger Amorim Brandão, Paulo Tarso Sanches de Oliveira

Tema

08 - Desastres compostos: sinergia entre diferentes tipos de risco

Resumo

Droughts and floods are often treated as separate hydrological extremes, although their temporal sequencing can create additional risks when catchments shift from water scarcity to excess. This study investigates hydrological drought-to-flood transitions across Brazilian catchments and evaluates how their frequency and timing vary among hydrological behavior groups. We used daily streamflow records from 476 catchments from CAMELS-BR, covering 1981?2024 and restricted to basins with low flow regulation. Streamflow droughts were identified from the 30-day moving average of daily discharge using a variable daily threshold based on the 20th percentile and a minimum duration of 30 days. Flood events were defined using the 50th percentile of annual maximum streamflow, considering independent events separated by at least 10 days. Transitions were classified as rapid when flood onset occurred within 14 days after drought termination, and seasonal when the interval ranged from 15 to 90 days. Transition times varied widely, from 6 to 1781 days, with a median of 121 days and a mean of 207 days. Within the 90-day window, seasonal transitions were approximately 25 times more frequent than rapid transitions, representing 96.1% of events. Rapid transitions were more frequent in Transitional Dry Catchments, whereas seasonal transitions peaked in Transitional Wet Catchments. These results indicate that drought-to-flood transitions in Brazil are predominantly subseasonal and are shaped not only by climate variability, but also by catchment storage, connectivity, and runoff-generation processes. The findings support integrated assessments of compound hydrological extremes and provide a basis for improving drought and flood risk management in Brazil.