Improving the understanding of rainfall-runoff processes: Temporal dynamic of event runoff response in Loess Plateau, China.

Enhancing the understanding of the rainfall-runoff temporal dynamics in semi-arid and semi-humid regions is crucial for flood disaster mitigation. Loess Plateau is a unique environment within semi-arid and semi-humid regions, characterized by its deep loess soil, prevalent short-duration intense rainfall, and changes in underlying surface conditions. In this research, 25 catchments from the Loess Plateau were chosen to examine the temporal variations in event runoff responses across different time scales. The study analyzed event rainfall characteristics, catchment wetness conditions, and runoff responses to identify the factors influencing event-to-event variability, seasonal patterns, and long-term shifts in runoff behavior. The results show that the event runoff response exhibits distinct patterns across different ecological regions of Loess Plateau. In the Loess Hilly and Gully region, the event runoff response is primarily influenced by rainfall intensity characteristics and occurs due to infiltration excess. In the River Valley Plain and Earth-rocky Mountainous regions characterized by a humid climate, event runoff response is influenced by pre-event soil moisture and shows a strong correlation with rainfall volume. In the Loess Hilly and Gully region, catchments experience a noticeable transition between saturated and unsaturated states over long-term changes, driven by the combined impacts of land use and climate changes. The study provides insights into the mechanisms behind runoff generation at the catchment scale and offers valuable information for flood forecasting in semi-arid and semi-humid regions.