Quantifying contributions of climate change and local human activities to runoff decline in the upper reaches of the Luanhe River basin

Climate change and local human activities are regarded as the two main factors influencing runoff. Using observed runoff, there is a statistically significant decreasing trend for annual and monthly runoff detected by the Mann-Kendall’s test, in the upper reaches of Luanhe River basin (URLRB), 1954–2000. With the break point analysis, the whole time series are divided into two sub periods: “natural period (1954–1970) and “impact period” (1971–2000). “Natural runoff” from 1954 to 2000, is reconstructed by the variable infiltration capacity (VIC) model, in which the model parameters are calibrated in “natural period” representing the natural watershed characteristics without the impact of local human activities. By comparing the difference between observed runoff and “natural runoff” in “impact period”, the contributions of climate change and local human activities are quantitatively separated. The results indicate that climate change and local human activities account for 49% and 51%, respectively, on the annual runoff decrease in the URLRB. That means the effects of climate change on runoff are roughly the same as the effects of local human activities. Climate change results in decrease in monthly runoff; and local human activities mainly affect flood season runoff. The results could be a reference for water resources projection and management in the URLRB and other catchments in northern China.