Impacts of climate change and human activities on hydrological components in Luanhe River basin, China

Climate change and human activities have been widely accepted as two main factors that deeply influenced hydrological processes, but quantifying impacts on river runoff and hydrological components have not been fully revealed. Investigating the relationships between these components and the impact factors have great importance for future watershed management. Using the variable infiltration capacity (VIC) model, this study quantified the impacts of climate change and human activities on hydrological components in Luanhe River basin, North China. Human activities were separated into land cover change and other impact factors, such as irrigation and inter-basin water transfer project. We first analyzed the trend and break points of annual runoff using the Mann-Kendall's test and double-mass curves, and divided the time series into one "natural period" (1960-1979) and two "impact periods" (1980-1997, 1998-2016). The parameters of VIC model calibrated by "natural streamflow" from 1960 to 1979 represented the natural watershed characteristics without the influence of human activities. Results indicate that: 1) other impact factors (the Luanhe-Tianjin Water Diversion Project) had become the main cause of river runoff reduction over climate change and land cover change in the second impact period (1998-2016). 2) The runoff change affected by climate change was dominated by the variation of rainfall. Temperature rising also influenced the basin runoff in a certain way. 3) Climate change showed more extented spatial impacts on the four hydrological components, i.e. evapotranspiration, surface runoff, baseflow, and soil water content, than land cover change. Otherwise, the impacts of land cover change on evapotranspiration were stronger than climate change. These results are helpful to find out the hydrological components responses to changing environment, and provide implications for future water resources planning and management, especially at watershed level.