Changes of dominant periods of flood disaster in China during 1644-2004

Based on the data of the number of flood hazard counties during 1644-1839 and 1840-1949 and the area of flooded cropland during 1950-2004,the periodic features of flood disaster over China since 1644 are analyzed in this paper.A uniform flood disaster series is established by the rermving trend from the on ginal data and standardizing the data then in each interval in order to make the data from different sources comparable and remove the effect of human factors.The methods of the classical spectrum analysis and Butteiworth filter are used to analyze the standard series.It is found that(1) changes of flood disaster over China during 1644-2004 is an integration of the different time-scale periodic oscillations dominated by the scales of 80 year,50-year,30-year and 20-year,and (2) the dominant periods are different in different times,which are the centennial scale oscillation during 1644-1833,and the 20-year scale periodic oscillation is sensitive in addition to the centennial scale oscillation during 1833-1920,while the interdecadal periodic oscillation is dominant after 1921 within which a change from 20-year to 30-year scale occurred in 1947.