Abstract: In this paper, the change and periodicity of average annual runoff volume and its main affecting factors along the Ningxia-Inner Mongolia section of the Yellow River were lucubrated based on 46-year (from 1961 to 2006) average annual runoff volume data measured at Qingtongxia and Toudaoguai hydrological stations, and the multi-temporal scales were analyzed. The results show that the change of average annual runoff volume at these two stations at different temporal scales was synchronicities. After analyzing the wavelet variance plots, it was found that there were 18-year and 31-year periodic fluctuations of annual runoff volume. The results were tested and verified with the process line of the real part of wavelet to obtain the change trend of annual runoff volume at these two stations, and it was predicted that a low flow will continue along the Ningxia-Inner Mongolia river section in next few years. Reduction of annual runoff volume of the river section was mainly caused by the decrease of precipitation, increase of water consumption and operation of reservoirs. The study results can provide the references for conserving water resources, controlling sediment and predicting annual runoff volume along the Ningxia-Inner Mongolia section of the Yellow River.

Key words: change of runoff volume, wavelet analysis, periodicity, Ningxia-Inner Mongolia section, Yellow River