Effects of climate change and human activities on runoff in the Beichuan River Basin in the northeastern Tibetan Plateau, China

Climate change and human activities are considered to be the main drivers of runoff changes. Assessing their contributions is important for maintaining the integrity of the water cycle process and promoting the healthy management of water resources. But the contributions of these two factors in the Beichuan River Basin remain unclear. In this study, hydrological and meteorological data from six sub-basins (Niuchang, Xiamen, Heilin, Qiaotou, Dongxia, and Chaoyang) during 1961-2013 were studied to elucidate upon the effects of these processes. Mann-Kendall tests showed that runoff in the Beichuan River Basin showed a downward trend over the study period and revealed that abrupt changes occurred in 1972 and 1989. Therefore, the study period was divided into two periods: a base period and a change period (periods I and II). A climate elasticity model and hydrological sensitivity analysis were used to estimate the contributions of climate change and human activities. We found that the dominant factors in changing runoff were human activities. Due with the conversion of cropland to forest and grassland and increases of construction land, during the change period water supply increases evidently. Among the basin regions, the Chaoyang sub-basin showed the greatest runoff decline and an abrupt change in 1989, and human activities had the greatest contribution to runoff change in this sub-basin. In addition, the conversion of cropland to forest and grassland was most evident in the Chaoyang and Qiaotou subbasins, and the area of construction land in these two regions increased greatly during the change period.