Methods
Introduction of the study area
The Yellow River is the second largest river in China
which originates from the Tibetan Plateau, flows eastwards
through the Loess Plateau and the North China
Plain, inrushes into the Bohai Sea at Kenli County,
Shandong Province, with the mainstream length of 5464
km and basin area of 752 000 km2. The river is divided
into the upper, middle and lower reaches based on its
geomorphology and climatic conditions. According to
the Yellow River Water Resources Bulletin of 2008, the
upper reaches are the section from the river source to
Toudaoguai, where the climate is arid with an annual
average precipitation of 396 mm. The middle reaches
stretch from Toudaoguai to Huayuankou; this section is
mainly located in the Loess Plateau with lots of tributaries.
The climate is semiarid and arid with an annual
average precipitation of 516 mm. The lower reaches
stream down from Huayuankou; the climate is humid
with an annual average precipitation of 648 mm.