Evaluating the contributions of climate change and human activities to runoff in typical semi-arid area, China

Climate change and human activities have been widely recognized as two major factors that deeply influenced hydrological processes. It has great importance to evaluate and identify the contributions among distinct driving factors, which could help carry out better regional water resources management regulation. In this study, we used the Variable Infiltration Capacity (VIC) model to quantify the contributions for different climatic variables and human activities to runoff in the Luanhe River basin (LRB) with semi-arid climate, northern China. Our intention is to detect the multiple impacts of climate change (CC), such as precipitation change (PC) and temperature rising (TR), and human activities (HA), including land use/cover change (LUCC) and direct human activities (i.e., water withdrawal and inter-basin water diversion, DHA), on runoff variance. The natural period (1961-1979), weak impact period (1980-1997) and strong impact period (1998-2016) were divided based on the double-mass curves and Mann-Kendall's test of observed runoff data from 1961 to 2016. The results indicated that, 1) compared with climate change, human activities were the major factors decreasing the runoff, which contributed more than 60% to the runoff reduction in two impact periods; 2) the runoff variation affected by climate was ruled by the precipitation change positively and strongly, and the impacts of precipitation and temperature strengthened with time. 3) During the strong impact period, the direct human activities have presented the most contribution on runoff reduction, which may result from the water diversion and water withdrawal. The influence of LUCC on runoff was mainly due to the conversion between grassland and cropland. These results would be helpful for policymakers and researchers to better understand the responses of runoff to this changing environment conditions and provide implications for future water resources planning and management at the basin scale.