Identifying Contributions of Climate Change and Human Activity to Changes in Runoff Using Epoch Detection and Hydrologic Simulation

Runoff in major rivers in China has been decreasing in recent decades. The attribution of hydrologic variability to human activity or climate change is a challenging problem and an active research area. In this study, a sequential cluster analysis method was used to detect undisturbed parts of the record for the Kuyehe River catchment in China. The variable infiltration capacity (VIC) land-surface model was calibrated and verified using observed hydrometeorological data from a period with relatively little human-induced disturbance. The calibrated VIC model was then used to simulate natural runoff during the human-regulated period. Results indicate that the recorded runoff at Wenjiachuan station had significant decline trend of −1.34 mm/year. Time series of runoff was detected and divided into three epochs at two critical years of 1980 and 1998. The VIC model performed well in simulating monthly discharges in the catchment, both Nash and Sutcliffe efficiency (NSE) critera in calibration (1955 to 1969) and verification (1970 to 1979) were above 70% while relative errors (REs) were less than 5%. Human activity was the main driver behind 68% of the runoff reduction that occurred for the period of 1980 to 2008.