Climatic and anthropogenic impacts on runoff changes in the Songhua River basin over the last 56 years (1955–2010), Northeastern China

Runoff of some rivers in the world has decreased significantly due to climate change and enhanced human activities, resulting in severe eco-environmental problems. As a large Asian river with a channel length of 2309 km and a basin area of 5.568 x 10(5) km(2), the Songhua River basin is an important bread basket in China. Although its runoff has experienced dramatic changes over the last decades, the relative importance of climate and human activity on the runoff changes has not been assessed heretofore. The purpose of this study is to decouple the relative impacts of precipitation, evapotranspiration (ET), and human activity on the runoff changes in the river basin using a SCRCQ method. Based on annual runoff dataset at 3 gauging stations on the main stem channel during the period 1955-2010, three turning years of runoff changes were detected that divided the entire time period into four parts for the above Dalai (1963, 1982, and 1998) and Haerbin-Jiamusi (1966, 1980, and 1998) sub-basins. While for the Dalai-Haerbin sub-basin, only one turning year of 1988 was detected. The first period was taken as the reference baseline period while the others regarded as measure periods. Based on mean annual precipitation and mean annual reference crop ET observed at 62 meteorological stations during the period 1955-2010, the relative impacts of precipitation, evapotranspiration and human activities on runoff changes were assessed. For the runoff changes in the above Dalai and Haerbin-Jiamusi sub-basins, the results show that the precipitation impact ranged from 3.3% to 24.7% and from 15.4% to 33.9%, respectively, and the impact of ET ranged from 0.6% to 10.8% and from -7.3% to 9.8%, respectively. In comparison, the anthropogenic impact ranged from 64.8% to 96.1% and from 56.3% to 91.9%, respectively. For the Dalai-Haerbin sub-basin, the impacts of precipitation, evapotranspiration and human activities on the runoff changes were 29.7%, -15.6% and 85.8%, respectively. Human activities have become the most important factor in controlling runoff changes in the river basin. The magnitude of human impact reached its maximum in the 1990s, and then decreased remarkably as a result of the implementation of some new measures, such as water-saving irrigation, wetland conservation and restoration, and reforestation, in agriculture production and environment protection. Given the severe water stress, anthropogenic impact on runoff changes in the Songhua River basin must be given more attention in the future. (C) 2015 Elsevier B.V. All rights reserved.