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Flood and Drought Variability in China's Yangtze Delta
Zhang, Q., Chen, J. and Becker, S. 2007. Flood/drought change of last millennium in the Yangtze Delta and its possible connections with Tibetan climatic changes. Global and Planetary Change 57: 213-221.

What was done
Flood and drought histories of the past thousand years in China's Yangtze Delta were developed, according to the authors, "from local chronicles, old and very comprehensive encyclopaedia, historic agricultural registers, and official weather reports." Thereafter, "continuous wavelet transform was applied to detect the periodicity and variability of the flood/drought series" -- which they describe as "a powerful way to characterize the frequency, the intensity, the time position, and the duration of variations in a climate data series" -- and, finally, the results of the entire set of operations were compared with two one-thousand-year temperature histories of the Tibetan Plateau -- northeastern Tibet and southern Tibet.

What was learned
Zhang et al. report that "colder mean temperature in the Tibetan Plateau usually resulted in higher probability of flood events in the Yangtze Delta region," and they say that "during AD 1400-1700 [the coldest portion of their record, corresponding to much of the Little Ice Age], the proxy indicators showing the annual temperature experienced larger variability (larger standard deviation), and this time interval exactly [our italics] corresponds to the time when the higher and significant wavelet variance occurred." In contrast, they report that "during AD 1000-1400 [the warmest portion of their record, corresponding to much of the Medieval Warm Period], relatively stable changes of climatic changes reconstructed from proxy indicators in Tibet correspond to lower wavelet variance of flood/drought series in the Yangtze Delta region."

What it means
Contrary to climate-alarmist contentions that warmer temperatures lead to more frequent and intense floods and droughts, this evidence from China suggests just the opposite. In addition, the proxy temperature records employed by Zhang et al. indicate that the warmest 50-year periods of the past millennium occurred during the Medieval Warm Period and not during the 20th century in both temperature histories, which is also just the opposite of what climate alarmists typically contend for most of the world.

Reviewed 30 April 2008