Changes in components of the hydrological cycle in the Yellow River basin during the second half of the 20th century

The Yellow River basin of China, located in the semi-humid, semi-arid and and climatic zones, is now confronted with serious problems of water deficit. With regard to intensified human activities and climatic change, knowledge about changes in the regional hydrological cycle should be seen as a key requirement in searching for an adaptation strategy in water resource use. This paper attempts to detect trends associated with hydrological cycle components in the region. The hydrological cycle components are derived from monthly precipitation and runoff date, based on the schemes proposed herein. Two methods, including linear regression and Mann-Kendall, have been applied to the detection of trends in the hydrological cycle components. For the Lanzhou station, only surface runoff showed a decreasing trend. As for Huayuankou station, the results have shown that natural runoff, surface runoff and groundwater runoff all have significant decreasing trends, whereas the decreasing trend of the other components is not significant. Impacts of human activities, climatic change and annual runoff coefficient change on the hydrological cycle components are also discussed. The study suggests that increasing water resources development and utilization is the most important factor in causing the frequent drying-up in the main course of the Yellow River. Moreover, the similarities of the trends in precipitation and natural runoff suggest a linkage between climatic change and hydrological cycle change. Copyright (C) 2004 John Wiley Sons, Ltd.