Changes and implications of the relationship between rainfall, runoff and sediment load in the Wuding River basin on the Chinese Loess Plateau

The interactions between precipitation, runoff and sedimentation could reveal information about the processes of runoff and sediment production and the environmental evolution mechanisms of basins. Based on the hydrometeorological data collected over a long-term time series (1955-2012) which has been divided into five periods (P1 (1956-1969), P2 (1970-1979), P3 (1980-1989), P4 (1990-1999) and P5 (2000-2012)), changes and implications of the relationships between precipitation, runoff and sediment load (precipitation-runoff-sediment relationships) were studied in the Wuding River basin, China. Conclusions are as follows. (1) There is no obvious change occurs on the distribution of annual precipitation during 1955 to 2012. However, the annual runoff and sediment load are significantly decreased by 51.9% and 86.4%, respectively, from P1 to P5. (2) Under the same precipitation conditions, the runoff and sediment present overall decreasing trends. Decrease in the runoff was greater than that in the sediment load. The incoming sediment coefficient (ISC) reduced by 69.2%, indicating that the sediment transport ability per unit runoff was weakened. The significant reduction of ISC along with the decrease of the runoff amount caused the sediment brought into the Yellow River (STWY) decreased from P1 to P5. (3) Soil conservation measures played a critical role for the changes in precipitation-runoff-sediment relationships. Due to the rapid increases in the available storage of check dams in P2 and P5 and the areas of forest and grassland in P2, relationships among the precipitation, runoff and sediment has drastically changed. Decrease of the effects on sediment interception in check dams caused the sediment increased from P3 to P4. (4) Decreases of runoff and sediment load, and changes in their relationships would continue with the sustainable management of slopes and gullies. The potentially detrimental changes in the storage of check dams and those in runoff and sediment influenced by extreme weather conditions should be monitored and managed.