VARIATION OF DROUGHT AND FLOOD OVER THE LAST MILLENNIUM IN POYANG LAKE BASIN BY R/S ANALYSIS
Wang Huai-qin · Changjiang liuyu ziyuan yu huanjing · 2015
Using the historical documents from 1160 to 1950,the characteristics of floods and droughts in the Poyang Lake basin are studied.Firstly,the flood and drought disasters were classified,according to the description of historical documents.Secondly,by using the method of wavelet analysis,the method of correlative dimension and the method of fractal dimension of time,the fractal dimension of flood and drought disaster of Poyang Lake were studied.Thirdly,Hurst index of decadal floods and droughts was calculated by using the R/S analysis method.Combined with the results of trend analysis and wavelet analysis,the flood and drought of Poyang Lake were predicted and verified by using the SPI index.The conclusions are as follows:1.the proxy data of the Poyang Lake basin inevitable has some missing data during the long period because of various reasons.In the social unrest periods,the data missing rate maybe even higher.It will have poor reliability for the analysis of the proxy data as a whole because of the missing data.So the proxy data would be smoothed to reduce the uncertainty.Literature proxy data on flood record rate have certain continuity between adjacent periods,analysis through the periodic variations of the smoothed data sequences,with better credibility,to analyze and estimate the change trend of the sequence of the stage,has certain scientific significance.2.From 1160 to 1940s,the intensity and frequency of flood and drought in the Poyang lake basin and sub-basin showed a trend of fluctuations and had an obvious characteristic of cyclic changes,3-6decades and passed 95%reliability analysis.3.The drought has the period of quasi-3-6decades,and the flood has the quasi-3-6decades also.4.The Hurst indexes of drought ranged from 0.7to 0.8,while the indexes of flood ranged from 0.8to 0.9.The flood and drought time series have the nearly linear fractal characteristics.5.According to the historical data,the frequency of flood and drought are predicted to show a rising trend.The predicted results are matched with the observation facts.It means the R/S analysis method can be used in the prediction of floods and droughts in the Poyang Lake Basin.