Research on long-term streamflow variation characteristics in Poyang Lake watershed based on wavelet analysis

Based on the monthly runoff series (1955-2003) of the three gauging stations in Poyang Lake watershed, the wavelet transform method was adopted to analyze the temporal trend and periodic variation of the streamflows in the watershed. Result from Multi-Resolution Analysis (MRA) using the Db3 wavelet function indicates that the long-term trend of streamflow in the Poyang Lake watershed show ascends before 1998 while descends thereafter, and the descending rate is slower than that of rising rate. Causes for this mainly come from the long-term uptrend of precipitation and downtrend of actual evapotranspiration, and both trends turn over at 1998. Periodicity analysis from continuous wavelet transform (CWT) revealed that there exist 25-26 years´ first dominant periods and 8 years, 3-4 years´ sub-dominant periods at all three stations. According to the variation of periodicity, it can be anticipated that the Poyang Lake watershed will be in the relative arid climate in the next 10 years, and the higher frequency and severity of droughts will persist. The watershed will enter into a humid climate and high-flow period at about 2018.