Runoff characteristic in flood and dry seasons based on wavelet analysis in the source regions of Yangtze and Yellow River

By decomposing and reconstructing the runoff information from 1965 to 2007 of the hydrologic stations of Tuotuo River, Zhimenda in the source region of Yangtze and Jimai, Tangnaihai in the source region of Yellow River with db3 wavelet, runoff of different hydrologic stations shows to be declining in the seasons of spring flood, summer flood and dry ones except for those in Tuotuo River. The declining flood/dry seasons series was summer >; spring >; dry; while runoff of Tuotuo River was always increasing in different stages from 1965 to 2007 with higher increase rate in summer flood seasons than that in spring one. Complex Morlet wavelet was selected to detect runoff periodicity of the four hydrologic stations mentioned above. Totally the periodicity was 11-12 years in the source region of Yellow River, while 4-6 years in spring flood seasons and 13-14 years in summer flood seasons in the source region of Yangtze River. The major periodicity in spring, summer and dry seasons was distinctive greatly in different basins.