Using hydrologic simulation to identify contributions of climate change and human activity to runoff changes in the Kuye river basin, China

Under the background of global climate change and local anthropogenic stresses, runoff has been in decline in most river basins in China over the past decades. Assessing the relative effect of climate change and human activities is essential not only for understanding the mechanism of hydrological response in the catchment, but also for local water resources management. The Kuye river, the first-order tributary of the middle Yellow river, has experienced significant runoff declines. In this study, the characteristics of hydro-climatic changes of the Kuye river catchment were analyzed based on the observed data for the period 1955-2010. Using the monthly climatic and hydrological data, the Yellow river water balance model (YRWBM) is calibrated and verified to a baseline period from 1955 to 1978. Subsequently, natural runoff for human-induced period (1979-1998) and strongly human-induced period (1999-2010) is reconstructed using the YRWBM model without considering local human impacts. Results indicate that the time series of runoff was divided into three periods at two critical years of 1979 and 1998. The YRWBM model performed well in simulating monthly discharges in the catchment, both NSES in calibration and verification were above 70 %, while RES in both periods were at less than 5 %. The absolute runoff reductions induced by climate change and human activities both have been growing. The percentage of runoff reduction attributed to climate variations from 60.56 % in human-induced periods to 43.50 % in strongly human-induced periods. At the same time the percentage of runoff reduction from human activities is from 39.44 % in human-induced periods to 56.50 % in strongly human-induced periods. Thus human activities demonstrated a dominant influence upon runoff decline gradually.