Speakers
Description
Sofia Ortenzi1,2, Lucio Di Matteo2, Corrado Cencetti2, and Christian Massari1
1 Research Institute for Geo-Hydrological Protection, National Research Council of Italy
2 Department of Physics and Geology, University of Perugia, Perugia
Understanding the thresholds for surface runoff generation is a complex task with important implications for flood forecasting, flash flood guidance, and soil erosion assessment. While several studies have identified threshold behaviour at the plot or small catchment scale, extending these approaches to larger basins remains challenging mainly due to the limited availability of soil moisture observations and the difficulty in consistently identifying rainfall–runoff events. In this study, a transferable procedure for identifying runoff generation thresholds at the catchment scale, integrating satellite-derived soil moisture data, is developed. The method is applied to six Italian catchments using SMAP L4 soil moisture data to derive the Antecedent Soil Moisture Index (ASI). Results show that while rainfall alone is insufficient to define runoff thresholds, combining rainfall depth with antecedent soil moisture conditions (ASI+P) reveals a clear threshold behaviour characterized by a nonlinear “hockey-stick” relationship, highlighting the key role of pre-event wetness conditions in controlling runoff generation. The proposed framework provides a consistent approach to analyse runoff generation processes at the basin scale and demonstrates the potential of satellite soil moisture data for improving flash flood guidance. Some questions remain open regarding the generality of the proposed empirical approach. In particular, it is still unclear which physical factors exert the strongest control on threshold behaviour and how these thresholds vary under different meteo-climatic conditions. Addressing these questions requires extending the analysis across a wider range of environmental settings. Future research will therefore focus on investigating runoff generation processes across European catchments to improve the understanding of the key controls governing runoff thresholds.