Background The rapid variation of runoff and sediment in the Yellow River have caused a major impact on the decision-making and practice of the Yellow River management, which have become a focus in the field of water science and environmental science. Due to the variations of runoff and sediment changes with time, state and process, the research of the evolution characteristics of the relationship between runoff and sediment transport is of great significance for revealing the mechanism of water and sediment variation.

Methods Combined with field investigation, the rainfall, runoff and sediment location observation data of the Yellow River in the past 100 years were statistically analyzed. The variation trend degrees of runoff and sediment were calculated based on long sequence and each period, and the diversity indicators were obtained as well. Furthermore, the erosion momenta of rainfalls in the typical tributary fields were calculated, and reduction benefits of water and soil conservation measures were computed by means of soil and water conservation analysis and evaluation.

Results 1) The change of the runoff and sediment in the Yellow River experienced a process from gradual to sharp change. Before the mid-1980s, the trend degree of runoff and sediment was close to zero. The trend degree of runoff and sediment turned into -0.281 1 and -0.297 0 during the period of 1987—1999, and changed to -0.384 5 and -0.790 1 since 2000. 2) By the great reduction of the runoff and sediment, the relationships between rainfall and natural runoff in the most tributaries have changed, while those between measured runoff and sediment have not been noticeably changed. Thus, the quantitative reduction of the runoff and sediment was uncoordinated with the qualitative change of correlativity between runoff and sediment transport. 3) The variations of runoff and sediment did not have complete synchronization on the time scale. The decrease in sediment transport was greater than the decrease in runoff by nearly 38% in Tongguan hydrological station, and changes in water and sediment did not alter the uncoordinated feature of the relationship between water. 4) It can be seen that under the strong interference of human activities, lots of triggered problems should be further explored in depth, such as prediction theory and method of runoff and sediment situation in complex basin system, response mechanism of water and sediment changes to conservation of soil and water, the threshold while the reduction of the sediment transport, and the changes of runoff generation mechanism in the Loess Plateau.

Conclusions This research systematically reveals the variation characteristics of the relationship between the runoff and sediment in the Yellow River, and the scientific issues are proposed, which can help to deepen the knowledge of the mechanism of the change of the water and sediment in the Yellow River.