In the upper reaches of the Lanzhou and Toudaoguai sections of the YRB, water resources are abundant; however, human activities have inevitably influenced the runoff. Large-scale human activities include hyper-irrigation and large hydroelectric projects. There are 24 reservoirs scattered throughout the YRB, with storage capacities exceeding 0.10 × 10⁹ m³. These reservoirs redistribute the seasonal and annual water discharges and sediment loads. Large hydroelectric projects (including reservoirs at Longyangxia, Liujiaxia, Qingtongxia, and Sanshenggong) are located in the upper reaches (Figure 1). The slope of the DMC in the Lanzhou section (Figure 10) decreases in 1993, indicating that the impact of human activities increased, reaching 74.87% (Table 5). This increase is mainly due to the Liujiaxia and Longyangxia reservoirs. The Liujiaxia and Longyangxia reservoirs were constructed above Lanzhou in 1968 and 1985, respectively. The Liujiaxia reservoir has a storage capacity of 5.7 km³ and a 147 m high dam wall. The Longyangxia reservoir (27.6 km³ storage capacity and a 178 m high dam wall) is a multi-year reservoir. The combined operation of these two reservoirs regulates the seasonal water discharge from the upper reaches to meet demands for agricultural irrigation; thus, these operations affect the middle and lower reaches (Chen 1997). Moreover, Figure 10 shows that the precipitation and runoff DMC in the Toudaoguai section is negatively correlated because runoff at Toudaoguai station is less than that at Lanzhou station. Human activities and underlying surface conditions directly reduce the runoff in this section. The hyper-irrigation area of the upper reaches of the YRB is approximately 1,230 km² according to statistical data from the Chinese Ministry of Water Resources. More than 94% of this area is located in the Toudaoguai section (Table 6). Hyper-irrigation directly reduces the regional water discharge due to water consumption by irrigation fields. The runoff decrease in the upper reaches has been affected by increasing water diversion from the main stream for irrigation and industrial utilization. Therefore, the impacts of human activities on runoff are most significant in the upper reaches. As a result, the runoff trends at three stations (Guide, Lanzhou, and Toudaoguai) in the upper reaches have declined. However, the annual precipitation trend at one station displayed a significant increase (Figure 4).