On the Use of the Distributed Hydrological Model QT-DREAM to Reproduce the Frequency Distribution of Observed Flood Peaks in Puglia and Basilicata (Southern Italy)

The design of flood hydrographs for specific return periods is crucial in hydrological studies, especially in poorly-gauged watersheds. Exploiting the background of the distributed grid-based hydrological model DREAM, to estimate flood hydrographs for assigned return periods we propose the Q_T-DREAM, which incorporates high-resolution geomorphological data to reduce structural uncertainty compared to traditional empirical models. By combining Hortonian and Dunnian infiltration models, Q_T-DREAM allows a spatially-distributed assessment of runoff generation based on local climatic and geomorphological characteristics. Q_T-DREAM was applied on twenty gauged catchments located in Puglia and Basilicata regions (Southern Italy), characterized by climates ranging from semi-arid Mediterranean to humid continental. Flood hydrographs were generated by the model for nested sub-basins for return periods of 30, 200, and 500 years and compared with those calculated using runoff maps of the entire basin. Results demonstrate that the Q_T-DREAM model successfully reproduces the frequency distribution of observed peak floods, ensuring consistency between peak discharges estimated at sub-basin and entire basin scales. This study provides a significant contribution to the development of indirect methodologies for flood estimation in poorly-gauged watersheds, with potential implications for hydraulic risk assessment and flood mitigation planning. In particular, model outputs can be integrated with two-dimensional hydrodynamic models to provide detailed flood hazard mapping, enhancing its applicability for basin-scale flood risk assessment and mitigation.