An elasticity approach to quantify the effects of climate variability and ecological restoration on sediment discharge change in the Loess Plateau, China

Suspended sediment yields (SSY) respond strongly to ecological restoration (ER) efforts, and significant improvements in SSY control have been achieved in the Loess Plateau of China. However, it remains challenging to quantify the net impacts of ER on SSY. Here, we study the elasticity of sediment discharge, by associating SSY change to climate variability and ER over the period 1950s to 2014. All ten of the sub-catchments studied experienced significant decreases in annual SSY, streamflow and suspended sediment concentration. Our results strongly support the hypothesis that changes to both streamflow volumes and to the suspended sediment concentration versus water discharge (C-Q) relationships result in reduced SSY, so that streamflow is reduced but runs clearer. We find that two of the ER strategies resulted in weaker relative impacts of climate variability, largely by reducing streamflow (by 55% to 75%). Meanwhile, ER predominantly decreased SSY (by 63% to 81%). Regarding ER practices, (i) the predominant measure acting to reduce SSY changed, over time, from engineering to reforestation; (ii) check-dams preferentially act to regulate the C-Q relationships whereas reforestation preferentially acts to moderate streamflow. Overall, our results suggest that a combination of engineering and vegetation measures is critical to achieving high-efficiency ER. While change to the ER strategy increased the efficiency of streamflow for SSY control, water discharge costs increased from 5.2 to 6.4 m³/t, owing to the continuous decreases in SSY. Conflicting demands for water necessitate that further ER should target precision management by revegetation of targeted areas in the Loess Plateau.