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A Two-Century History of Rainfall in Zimbabwe
Therrell, M.D., Stahle, D.W., Ries, L.P. and Shugart, H.H. 2006. Tree-ring reconstructed rainfall variability in Zimbabwe. Climate Dynamics 26: 677-685.

Climate alarmists typically claim that periods of extreme dryness and wetness (droughts and floods) become more frequent and/or severe with global warming. But is this true?

What was done
In a study that allows us to test this claim for a part of southern Africa, the authors developed "the first tree-ring reconstruction of rainfall in tropical Africa using a 200-year regional chronology based on samples of Pterocarpus angolensis [a deciduous tropical hardwood known locally as Mukwa] from Zimbabwe."

What was learned
Therrell et al. report that "a decadal-scale drought reconstructed from 1882 to 1896 matches the most severe sustained drought during the instrumental period (1989-1995)," and that "an even more severe drought is indicated from 1859 to 1868 in both the tree-ring and documentary data." They say, for example, that "the year 1860, which is the lowest reconstructed value during this period was described in a contemporary account from Botswana [where part of their tree-ring chronology originated] as "a season of 'severe and universal drought' with 'food of every description' being 'exceedingly scarce' and the losses of cattle being 'very severe' (Nash and Endfield, 2002)." At the other end of the moisture spectrum, they report that "a 6-year wet period at the turn of the nineteenth century (1897-1902) exceeds any wet episode during the instrumental era."

What it means
For a large part of central southern Africa, it is clear that the supposedly unprecedented global warming of the 20th century has not resulted in an intensification of extreme dry and wet periods. If anything, just the opposite appears to have occurred.

Nash, D.J. and Endfield, G.H. 2002. A 19th-century climate chronology for the Kalahari region of central southern Africa derived from missionary correspondence. International Journal of Climatology 22: 821-841.

Reviewed 20 September 2006