Impact of ENSO Events on Flood/Drough Disasters ofUpper Yangtze River during 1470—2003
ZHANG Qiang~1, JIANG Tong~1, WU Yi-jin~2(1. Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing Jiangsu 210008, China;2. Institute of Historical Geography, Wuhan University, Wuhan Hubei 430072, China)
Climatic indicators based on proxy historical flood/drought index series (1470-2003) in the Yangtze River and ENSO (El Nio/Southern Oscillation) index series (1868_2003) are statistically analyzed to detect a long-term variability of the floods/droughts and ENSO events and to identify the tele-connections between ENSO and flood/drought series in the upper reaches of the Yangtze River. The results show that the main flood variation cycle is longer than that of ENSO events. The former shows the periods of 16.69, 5.09 a and 10.47 a (over confidence level of 99%), while the latter shows the periods of 5 a, ～10～12 a and ～10 a. Cross-spectral analysis results indicate the ENSO change and flood/drought variation are significantly correlated at ～5-year period and ～10～12 years period. Therefore, based on the correlation analysis, spectral analysis and cross-spectral analysis, it can be concluded that the response of the floods/droughts along the middle Yangtze River to the effects of ENSO events is not only immediately occurred (about 3 a), but also can be somewhat long-lived (about 5 a or 10～12 a). The results also explicate that the shorter the interval of ENSO event, the sooner the following flood/drought respond and vice versa. Flood could delay if the survival of ENSO event is longer. Eastern Asian summer and winter monsoons are influenced by ENSO through the strength of the subtropical high in the western Pacific region, which can possibly serve as the physical mechanism of the phenomenon mentioned above.