Characterizing the Seasonal Changing Patterns of Hydrological Variables in the East River, Southern China

Trends and variability of hydrological variables can reflect the redistribution of seasonal patterns that can be caused by both climatic and anthropic factors. In this paper, China’s East River, the most regulated tributary in the Pearl River Delta (PRD), is selected to be a typical study case. Annual and seasonal-scale analyses of the river regime are performed, in conjunction with a correlation analysis between runoff and suspended sediment concentration (SSC). Noteworthy results include the strong increasing trends in dry season (October–March) runoff, as well as a significant decreasing trend in annual and wet season (April–September) SSC. Moreover, the continuous wavelet transform, runoff, and SSC display a degenerative annual fluctuation signal gain and a nearly total signal loss after 1990, respectively. All these results can be ascribed to an intra-annual redistribution of hydrological series, which bridges the gap between the wet and dry season and leads to a weakened seasonal difference. Furthermore, a changing correlation is detected with sediment rating curve at the seasonal scale. Finally, the river regime index (RRI) is calculated to quantify the impacts of river regulation. The results indicate that the East River is becoming a more uniform regulated river. Precipitation series, the most representative hydrological signal of climate factors, show no obvious temporal variations at the annual or seasonal scale over the whole study period. Therefore, the seasonal pattern alteration can be mainly attributed to human activities, in particular the construction of reservoirs in the East River.