Quantifying the contribution of climate- and human-induced runoff decrease in the Luanhe river basin, China

Climate variability and human activities are two main factors influencing hydrological processes. For more reasonable water management, understanding and quantifying the contributions of the two factors to runoff change is a prerequisite. In this paper, the Budyko decomposition hypothesis and the geometric approach were employed to quantify climate change and human activities on mean annual runoff (MAR) in six sub-basins of Luanhe river basin. We split a long-term period (1956–2011) into two sub-periods (pre-change and post-change periods) to quantify the change over time. Observations show that annual runoff has had a decreasing trend during the past 56 years in the Luanhe river basin. Based on a geometric approach, the climate impacts in these six sub-basins were 7–49%, and the contributions of human activities were 51–93%, approximately. According to the Budyko decomposition method, impacts of climate variation accounted for 15–40% of the runoff decrease, and the contribution of human activities was 60–85%. Both methods were simple to understand, and it is feasible to separate the climatic- and human-induced impacts on MAR. This study could provide significant information for water resources managers.