Abstract: Analyzing the changes and synchronicity in the flood elements of a Loess Plateau watershed is essential for a scientific understanding of the hydrological effects of ecological management in this region, and it is of great significance for improving the level of flood control and disaster reduction. This paper identifies and examines the annual maximum flood events, characteristic elements, and non-consistency characteristics in a river basin based on the hydrograph recession algorithm, through a case study of the Kuye River, a tributary of the Yellow River. We evaluate the changes in intensity of different flood characteristic elements using the constructed range of variability approach for flood characteristic index, and explore synchronization characteristics between these elements using the gray relational degree method. The results show that the flood characteristics take a significant decreasing trend with two-stage variations, and that human activities－such as water and soil conservation measures, land retirement for afforestation and grassland rehabilitation, and coal mining－have synergistically changed the intensity and characteristics of flood events in the basin to a moderate degree. A high degree has remained of the change in the synchronicity of flood peaks, flood volume, and flood frequency; the change rate has grown since 1999. Thus, great attention should be paid to the risk of medium and small floods.

Key words: flood elements, evolution, synchronicity, hydrograph recession algorithm, range of variability approach