Background The northern slope of Qilian Mountains is the source of many rivers in Hexi Corridor, as an important ecological security barrier in western inland area of China, which undertakes the diverse ecological functions such as water conservation, biodiversity protection. In recent 20 years, Qilian Mountain experienced a conversion from disordered exploitation of natural resources to the gradual restoration of ecological system. Our study was conducted to provide a technical basis to scientifically evaluating the effects of ecological restoration and effectively controlling the soil and water erosion in Qilian Mountain National Park.

Methods In this study, five representative basins were selected, to investigate the spatial and temporal variations of runoff, sediment and intensity of soil erosion using the methods of anomaly analysis and variance analysis, based on the runoff, sediment and precipitation data measured at five hydrological stations including Zamusi, Jiutiaoling, Yingluoxia, Changmabao and Dangchengwan in 2002—2021.

Results Compared to 2002—2011, the runoff in 2012—2021 observed from Zamusi station and Jiutiaoling station in Shiyang River Basin decreased respectively by 9.82% and 2.24%, while the runoff from Yingluoxia station in the Heihe River Basin increased by 11.88%, and the runoff from Changmabao station and Dangchengwan station in the Shule River Basin increased by 7.45% and 11.47%, respectively. Overall, the variations of runoff on the northern slope of Qilian Mountains showed the decreasing trend in the eastern yet the increasing trends in the middle and western, which were mainly caused by the regional climate change. Moreover, the sediment amounts at Zamusi, Changmabao, Dangchengwan station, decreased by 38.81%, 14.45%, and 40.16% respectively, yet at Jiutiaoling and Yingluoxia station increased by 79.35% and 63.96%, respectively. The intense rainfall may be the major driving force for the increasing sediment. Further, the average hydraulic erosion modulus for all the stations were less than 500 t/(km²·a) in the last 20 years, and its intensities were within the allowable erosion amount, but the intensity of soil erosion at Changmabao station had the great risk to exceed the allowable limit.

Conclusions The problems of ecological environment on the northern slope of Qilian Mountains has been initially settled, and the ecological environment has been improved. However, the Changma River basin is prone to the excessive soil and water loss and its effective control should be paid the great attention in future.