Spatiotemporal Variations in Annual Sediment Yield from the Middle Yellow River, China, 1950–2010

The Yellow River is an important source of sediment flux to oceans in the world, and approximately 90% of the sediment originates from the middle Yellow River, an area with known high rates of soil erosion and sediment delivery. Trends and interannual variations in sediment discharge have considerable implications for reservoir operation and river management of the lower Yellow River. The annual sediment discharge of four main stream stations and ten tributary stations was used to show the spatiotemporal variation in sediment yield and to quantify the relative contribution of precipitation change and human activities, especially the influence of vegetation restoration with implementation of the Grain for Green Project (GGP) in 1999. The Mann-Kendall and Pettitt tests were used to detect the abrupt change in sediment discharge since the 1950s. The annual sediment yield of the middle Yellow River has shown a significant downward trend, decreasing by an order of magnitude in the last decade (2000–2010) compared with the 1950s. Annual sediment yield was reduced by 95.5% from $\mathrm{3,887.0}\mathrm{t}·{\mathrm{km}}^{-2}·{\mathrm{year}}^{-1}$ in the 1950s to $174.7\mathrm{t}·{\mathrm{km}}^{-2}·{\mathrm{year}}^{-1}$ in the 2000s. The eastern part of the middle Yellow River basin showed the most significant decrease, with sediment yield decreasing up to 90% in the 2000s compared with the 1950s. Annual precipitation decreased by 7.3% in the periods 1980–2010 and 1959–1979. Human activities and precipitation explain 83.6 and 16.4% of the total reduction in sediment yield, respectively, using the double mass curve method. Annual sediment discharge decreased by $597\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$—from $660\times {10}^6$ in 1980–1999 to $63\times {10}^6$ in 2000–2010. Sediment deposition along the Longmen-Huayuankou section amounted to $120\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$ during 1980–1999 and $229\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$ during 2000–2010 based on mass balance. The additional $109\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$ of sediment was trapped following completion of the Xiaolangdi Reservoir in the Longmen-Huayuankou section. This explains 18.3% of the sediment reduction in the 2000s. Soil conservation practices have further reduced sediment discharge by $253\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$, which explains about 42.4% of the decrease ($597\times {10}^6$) during 2000–2010. A reduction of approximately $235\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$ occurred because of vegetation restoration driven by the Grain for Green Project, which accounted for 39.4% of the total reduction ($597\times {10}^6\mathrm{t}·{\mathrm{year}}^{-1}$) in the last decade compared to 1980–1999.