Separating the effects of revegetation and sediment-trapping dams construction on runoff and its application to a semi-arid watershed of the Loess Plateau

Runoff decrease triggered or exacerbated by human activities over the past decades on the Loess Plateau has been drawing nationwide concerns; quantifying human-induced runoff-altering factors is of great significance for decision-making on maintaining regional water, ecological and economic security. Sediment-trapping dams (STDs) construction and revegetation are the two major soil-water conservation practices regarded to have caused runoff reduction, while their hydrologic effects on the basin scale have not been separated quantitatively. In this study, we chose the Huangfuchuan River Basin as a case study area, and proposed a physically-based attribution framework with the ability to account for the hydrologic effects of STDs, revegetation, and climate change simultaneously and attribute runoff decrease of the basin among these factors. The model-based attribution results revealed that STDs construction caused a 45% (48%) runoff reduction from 1976 to 1988 to 1989–2000 (2001–2014) and revegetation was responsible for a 30% runoff decrease from 1976 to 1988 to 2001–2014, while the daily simulation implied that the hydrologic effect of revegetation affected daily runoff magnitudes more consistently than that of STDs. Our study demonstrates that STDs construction was the prime contributor to runoff decrease in the case study area and suggests that STDs should be taken into account in similar studies on the Loess Plateau in the future.