Yangtze 1/f discharge variability and the interacting river–lake system

SummaryThe intra-annual variability of the daily Yangtze discharge is analysed at the stations Cuntan and Yichang located in the upper reaches, and at Datong in the lower reach. The intra-annual power spectra at Cuntan and Yichang follow S(f) ∼ 1/f within time scales from one week to one year. Since precipitation in this region follows a white spectrum (S = const), the origin of 1/f-noise is possibly related to a broad distribution of time scales in the subsurface flow. The non-stationarity related to the 1/f-spectra complicates the application of statistical forecast methods. The spectrum at Datong is considerably steeper, f−3.5 up to two months. This variability is explained by storage and delayed release in the extended lake system connected to the Yangtze. A simple low pass filter suggests that the flow at this station responds to the input in Yichang with a time scale of eight days.