More than 50 years changes character and trend of the runoff in the source region of the Yellow River

The long-term changes character and trend of water cycle factors in the source region of the Yellow River (SRYR) is analyzed, basing on more than 50 years of the observed hydrological and meteorological data before 2009, by using climate diagnostics. The results show that the change trend of the annual precipitation in SRYR is not obvious. The most abundant annual runoff happens in 1980´s, annual runoff in 1960´s and annual runoff in 1970´s are followed. Since the year 1990, the total annual runoff volume of SRYR has been significantly reduced, few normal years of the annual runoff volume have appeared, but dry years are more and there are dramatic changes between the wet year and the dry year. The change trend of the time series of the nonuniformity coefficient of the annual runoff distribution in a year is downward, also the change trend of the time series of the runoff volume from July to October accounting for the annual total runoff volume is downward, but those decreasing trends are not significant.