Changes and controls of runoff generation in a watershed with substantial environmental change in China’s Loess Plateau

Abstract

Exploring the changes and controls of runoff generation holds critical importance for enhancing comprehension of hydrological processes in regions with significant environmental changes. Taking the Yan River watershed in the Loess Plateau of China as the study region, we recognized rainfall-runoff events and calculated three indices (event runoff coefficient ERC, event timescale Ts, and normalized event peak discharge Np) to characterize the runoff generation for 1961–2019. In particular, three parameters of SCS-CN model (initial abstraction Ia, potential maximum retention S, and curve number CN) were dervied to interpret the potential mechanism in runoff generation. Streamflow, surface runoff, and baseflow decreased significantly at rates of 0.33, 0.22, and 0.11 mm/a, respectively. Compared to the pre-change period (1961–1999), ERC and Np decreased by 51% and 6%, while Ts increased by 14% in the post-change period (2000–2019), indicating that the surface runoff hydrograph became flatter. S increased by 513% and CN decreased by 37%. Vegetation and population contributed to 38% and 35% of S change, 38% and 39% of CN change, respectively. The biological measures (vegetation restoration) play dominant role in accelerating water infiltration while the engineering measures (dams and terraces) enlarge water storage, which may largely interpret the changes in runoff generation. The methods and results are helpful for understanding hydrological processes and managing water resources in regions with substantial environmental change.