Characteristics of Runoff Variation of Poyang Lake Watershed in the Past 50 Years

Based on the monthly runoff series(1955-2003) of the three hydrological gauging stations,Waizhou,Lijiadu and Meigang within Poyang Lake watershed,statistical and wavelet methods are adopted to analyze the intra-annual,annual and periodic variation characteristics of the streamflows in the watershed for the last 50 years.The results show that:(1) the intra-annual stream flow presents a single-peak pattern with a peak value occurring in June,with the runoff in spring being larger than that in summer and autumn,and smallest,in winter.(2) In terms of the annual variation,stream flow increases towards 1998 and decreased thereafter,with the descending rate being smaller than the rising rate.(3) Variation of runoff exhibits a 25-year first dominant cycle and a 8-year or 3-4-year sub-dominant cycles at all three stations.The factors influencing the trend of stream flow are also investigated.Results indicate that the change of stream flow in Poyang Lake watershed is resulted from a combination of factors including climate(rainfall and evaporation),land cover and the construction of hydraulic engineering schemes,among which rainfall and evaporation are the dominant factors.The outcomes of this study are of primary importance for reasonable water resources management for Poyang Lake watershed.