Analysis of the Periodicity of Annual Extreme Runoff at Datong Station, Yangtze River, China

The periodicities of the annual maximum and minimum runoff time series at Datong hydrological station in the Yangtze River（P. R. China）were analyzed, according to the data from 1950 to 1995. The runoff of Datong hydrological station can be used to estimate the water discharges into the sea from the Yangtze River in a certain degree as there is no branch inflow from Datong station to the Yangtze Estuary. Two independent techniques were used in the analysis of time series: the conventional periodogram and the maximum entropy spectral analysis. The results reveal that the periods obtained in the time series at Datong station are related to the rainfall characteristics of the Yangtze River to a great extent. The long periods that are more than 10 years may be related to some climatic factors which are influenced by the solar activities. The short periods that are less than 10 years may be related to some factors which are affected by oceanic tides or human activities. The obtained periods not only reflect the periodicity characteristics of the water discharges into the sea from the Yangtze River, but also provide scientific evidence for the study of evolution of Datong reach of the Yangtze River.