Analysis on the fluctuation of inundated area of flood disaster at multi-time scales based on empirical mode decomposition method—A case study from Hunan Province

Empirical mode decomposition (EMD)method was used to study the fluctuation of inundated area of flood disaster from 1949 to 2002 in Hunan Province.The results show that the inundated areas fluctuate with 3 time scales,quasi-3-year,quasi-8-year and quasi-22-year.The analysis on the contribution ratio of fluctuations at different time scales indicates that the contribution ratio of quasi-3-year cycle is the highest meaning that quasi-3-year oscillation is the most prominent.The oscillations at different time-scales show that the amplitude of the fluctuation of inundated area has increased in recent years,and the great flood disaster maybe come forth in some years.The trends of oscillation at different time-scales suggest that the inundated area of flood disaster in Hunan Province be still in the period of increasing.The cause of the increase of frequency and intensity of flood disaster is further analyzed and some countermeasures are advanced to some extent.