Effects of climate change and human activities on runoff in the Nenjiang River Basin, Northeast China

Abstract. The Nenjiang River Basin (NRB) is an important grain-production region with abundant wetlands in Northeast China. Climate change and anthropogenic activities have dramatically altered the spatial and temporal distribution of regional stream discharge and water resources, which poses a serious threat to wetland ecosystems and sustainable agriculture. In this study, we analyzed 55-yr (1956–2010) rainfall and runoff patterns in the river basin to quantitatively evaluate the impact of human activities on regional hydrology. The long-term hydrologic series were divided into two periods: period I (1956–1974), during which minimum land use change occurred, and period II (1975–2010), during which land use change intensified. Kendall's rank correlation test, non-parametric Pettitt test and precipitation-runoff double cumulative curve (DCC) methods were utilized to identify the trends and thresholds of the annual runoff in the upstream, midstream, and downstream basin areas. Our results showed that the runoff in the NRB has continuously declined in the past 55 yr, and that the effects of climate change and human activities on the runoff reduction varied in the upstream, midstream and downstream area over different time scales. For the entire study period, climate change has been the dominant factor, accounting for 69.6–80.3% of the reduction in the total basin runoff. However, the impact of human activities has been increasing from 19.7% during the 1950s–1970s to 30.4% in the present time. Spatially, the runoff reduction became higher from the upstream to the downstream areas, revealing an increasing threat of water availability to the large wetland ecosystem in the lower river basin. Furthermore, the sustainable development of irrigated agriculture in the NRB will be a threat to the survival of the wetlands.