Temporal and spatial hydrological variations of the Yellow River in the past 60 years

Understanding water and sediment variations of the Yellow River is significant for future management of the river from perspectives of water resources utilization and ecology protection. The study characterized the temporal and spatial variations in its flow and sediment load based on the daily datasets of the past 60 years from all main-stem hydrological gauge stations, and proposed a new five-segment river reach division scheme instead of the traditional three- or four-segment division. Furthermore, we distinguished the key factors and their contributions that caused the flow and sediment variations, offering reference for the river management stra-tegies as per the local conditions. A significant decreasing trend in annual flow and sediment load was observed in the river basin, except for certain reaches in Segment 1 (upstream of Tangnaihai). The maximum flood-event duration decreased significantly in Segment 2 (from Tangnaihai to Shizuishan). The flood volume and sediment load during the maximum flood event also showed significant downward trend in Segments 2-5 (downstream of Tangnaihai). Operation of cascade reservoirs, especially in Segment 2, has smoothed the annual flow process in the upstream. Sediment trapping in the reservoirs had little effect on the change in sediment load, but reservoir regulation of flow greatly influenced siltation in the upstream river channel. Water abstraction has also played a significant role in flow variation. Consequently, the ratio of flood sediment load to annual sediment load decreased significantly in the upper reach, but increased significantly in the lower reach. Temporally, the recorded period was divided into three periods using change point detection: pre- 1987, 1987-1999, and post 1999. The ratio of flood volume to annual flow decreased significantly in the first two periods, and generally increased post 1999, with the impact of aforementioned anthropogenic activities.

Automated summary

Understanding the variations in water and sediment of the Yellow River is crucial for managing its water resources and protecting its ecology in the future. This study analyzed the temporal and spatial changes in flow and sediment load based on 60 years of data. It proposed a new division scheme for the river and identified the key factors contributing to the variations, providing insights for river management strategies. The study found significant decreasing trends in flow and sediment load, except for certain reaches. Reservoir operations and water abstraction were found to influence the variations, and there were changes in the ratio of flood volume to annual flow and flood sediment load to annual sediment load.