Determining relative contributions of climate change and multiple human activities to runoff and sediment reduction in the eastern Loess Plateau, China

Abstract

Fen River, as the second largest tributary of the Yellow River, is an important water source, and is of great significance for rational distribution of water and land resources in midstream and downstream of the Yellow River Basin. Under the combined influence of global warming and long-term human activities, runoff and sediment discharges in the Fen River Basin have decreased dramatically and the ecological environment deteriorated gradually. This study quantitatively evaluated the relative contribution of climate change, land use and other human activities (check dams, water consumption) on runoff and sediment variation in upstream, midstream and downstream using the double cumulative curve method, SWAT model and statistical analysis methods (multiple linear regression models). The results showed that annual precipitation presented an obvious decreasing trend, with a rate of 0.76 mm/a during 1960–2019. Runoff and sediment discharges in Jingle, Yitang and Hejin hydrological stations showed gradually downward trend from upstream to downstream, in which sediment reduced more significantly compared with runoff. Other human activities were the leading factors for runoff (sediment) reduction in P1 (1980–1999) and P2 (2000–2017), with the increasing relative contribution from 88.380% (94.248%) in P1 to 89.246% (95.897%) in P2, followed by climate change (especially precipitation), which were only 12.937% (5.938%) and 13.844% (3.582%), then land use change. The impact of climate change on runoff in upstream, midstream and downstream were 2.857%, 8.811% and 0.507% during P1-P2, while the relative contribution of other human activities increased to 65.714%, 79.903% and 91.635%. Sediment changes was also closely related to other human activities (99.190%, 100.846% and 101.884%), while the climate effect were −9.062%, −0.401% and −5.009%. In various other human activities, check dams and water consumption played significant important role on reducing runoff and sediment in recent decades.