ENSO事件对长江上游1470—2003年旱涝灾害影响分析

Impact of ENSO Events on Flood/Drough Disasters ofUpper Yangtze River during 1470—2003

对长江上游旱涝灾害时间序列(1470—2003年)及SST指数序列(1868—2003年)作统计相关与谱分析,探讨了长江上游旱涝灾害与ENSO事件的遥相关关系.结果表明:长江上游旱涝灾害主周期要大于ENSO事件的主周期,前者主周期主要为16.69a,5.09a以及10.47a,而后者主周期主要为5a,～10～12年以及～10a.交叉谱分析结果表明,长江上游旱涝灾害与SST在约5a以及约10～12a周期上呈现出显著的相关性.可以认为ENSO事件发生周期与生存周期的长短直接影响着长江上游旱涝灾害发生的周期与频率,并在5a以及10～12a的周期上表现出高的统计相关性.SST指数与长江上游旱涝灾害相关分析表明,ElNi no事件的发生使长江上游发生旱灾机率增大,而LaNi na事件的发生则使长江上游发生涝灾的机率增大.

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.