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

Abstract

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 strategies 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.