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Drought in Equatorial East Africa
Russell, J.M. and Johnson, T.C.  2005.  A high-resolution geochemical record from Lake Edward, Uganda Congo and the timing and causes of tropical African drought during the late Holocene.  Quaternary Science Reviews 24: 1375-1389.

What was done
Located on the border between Uganda and the Democratic Republic of the Congo, Lake Edward (0N, 30E) is the smallest of the great rift lakes of East Africa.  In the present study, the authors analyzed piston cores that were retrieved from the lake to derive a detailed precipitation record for this region over the past 5400 years.

What was learned
From the start of the record until about 1800 cal year BP, a long-term trend toward progressively more arid conditions was noted in the lake proxy record.  Thereafter, there followed what the authors term a "slight trend" toward wetter conditions to the present.  Superimposed on these long-term trends were evidences of major droughts of "at least century-scale duration," centered in the lacustrine records at about 850, 1500, 2000 and 4100 cal year BP.  In addition, multi-taper method spectral analysis revealed significant recurring drought periodicities of 725, 125, 72, 33, 29, 26, 19 and 16 years.  As for the possible causes of this variability, the authors say they are "poorly understood," but they postulate they are somehow linked to coupled ocean-atmosphere dynamics within the tropical monsoons.

What it means
The results of this study reveal that the past several hundred years have seen generally wetter climates in equatorial east Africa, free from the century-long droughts that plagued the region during much of the late Holocene.  Consequently, and in light of the region's historic drought periodicities, it would not be unusual for another century-long drought to grip the region sometime in the not-too-distant future; and when it does, you can bet the world's climate alarmists will be quick to claim CO2 is the culprit responsible for it.  But if we have little to no understanding of what caused such droughts in the past, it would be irresponsible to blame CO2 - or any other such factor - for the next big one that might occur.

Reviewed 9 November 2005