Changing trends and regime shift of streamflow in the Yellow River basin

Water shortages have become one of the most severe problems in semi-arid regions throughout the world. Although semi-arid regions have always been dry, human activities and climate change are acerbating the problem. In Chinese Yellow River basin, the river is the major source of freshwater for those living there, and they have long suffered from serious water shortages. However, increasing population and decreasing streamflow are making these shortages more acute. This study seeks to quantify changes in available water in the Yellow River basin over the last 100 years and attempts to determine causes for these changes. To do this, the study evaluated changing trends and regime shifts of streamflow using long term historical records at different hydrological stations in the Yellow River basin over the past century. The results show that annual streamflow has a significant decreasing trends (P < 0.01) in the mid-lower reaches of the basin. Streamflow decomposition by the breaks for additive seasonal and trend approach suggest that this trend can be decomposed into four distinct annual stages (1919–1933, 1934–1969, 1970–1986 and 1987–2011), while the seasonal component demonstrated an evident regime shift in 1986. This regime shift is mainly related to the construction of large reservoirs in the basin. The flow duration curves illustrate a decrease in the magnitude of streamflow over the last century with a relatively uniform flow regime at all stations. The reconstructed streamflow at Toudaoguai station suggests that agricultural irrigation is predominantly responsible for streamflow reductions between Lanzhou and Toudaoguai stations with approximately 9.1 km3/a of water extracted between 1997 and 2006. Meanwhile, a decrease of incoming water from upper reaches and soil and water conservation measures were responsible for the significant decline in annual streamflow at mid-lower reaches station. The result of this paper should be of use for water resources planning, watershed management and climate adaptation as they demonstrate how natural and anthropogenic drivers influence water availability in semi-arid regions.