Yangtze floods and droughts (China) and teleconnections with ENSO activities (1470-2003)

Climatic indicators based on proxy historical flood/drought index series (1470-2003) in the Yangtze river (China) and ENSO (El Ni (n) over tildeo/La Ni (n) over tildea) index series (1868-2003) are statistically analyzed to detect a long-term variability of the floods/droughts and ENSO events and to identify the teleconnections between ENSO and flood/drought series in the upper, middle and lower Yangtze River valley. In the lower and middle Yangtze catchments, El Ni (n) over tildeo shows a close relation with flood events and La Ni (n) over tildea correlates with drought events. However, the relationships are reversed for the upper Yangtze catchment. These relations are significant at > 90% confidence level based on chi(2) test. Spectral analysis shows that main flood/drought variation cycle is longer than that of ENSO events. The latter shows periods of 3-4 year, 5.67 years, similar to 10-12 years while the flood/drought cycle has periods of 16.69, 5.09 and 10.47 years (confidence level of 99%). Cross-spectral analysis results indicate the ENSO changes and flood/drought variation are significantly correlated at 5.04 year and similar to 10-12 years periods. Therefore, from the viewpoint of periodicity, ENSO episodes (El Ni (n) over tildeo and La Ni (n) over tildea) are in good teleconnection with floods/droughts in the Yangtze catchment. 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. The results tentatively suggest that the Chinese climatic index based on documentary records can be helpful for investigating the reconstruction of long-term ENSO activities. (c) 2005 Elsevier Ltd and INQUA. All rights reserved.