Geoscience Reference
In-Depth Information
Figure 23.8. Time series (1941-2008) of average normalized April-October rainfall
departure (
σ
) for twenty stations in theWest African Sudan-Sahelian zone (11
°
-18
°
N)
west of 10
°
E. (After Lele and Lamb,
2010
.)
from Lake Edward in Uganda indicated prolonged drought during the Little Ice Age
in central Africa, in contrast to wet conditions over Lake Naivasha in the Kenya Rift
Valley (Russell and Johnson,
2007
). Differential migration of the ITCZ and shifts in
the position of the ENSO system at this time could account for these differences. The
ultimate causes of the drought that became severe in the late 1960s were immediately
investigated (Dorize,
1974
; Roche et al.,
1975
; Dorize,
1976
;Pedelaborde,
1976
)and
are the subject of continuing study (Bell and Lamb,
2006
; Slingo et al.,
2008
; Tarhule
et al.,
2009
;Lele and Lamb,
2010
), including in the Horn of Africa (Segele et al.,
2009a
;Segeleetal.,
2009b
;Segeleetal.,
2009c
). An interesting attempt to place the
incidence of droughts within a time scale longer than a century was conducted by
Maley, whose pollen and limnological studies in Chad showed that high levels of Lake
Chad coincided with lowered temperatures in Europe at least for the past millennium
(Maley,
1973
;Maley,
1981
). Maley's concern with the possible influence of moist
tropical air on the late Pleistocene growth of ice caps in the Northern Hemisphere
(Maley,
1976
) may seem a far cry from present-day droughts, but two well-argued
reviews by Rognon (
1974
;
1976a
) of Saharan and global paleoclimates suggest that
the links may be there for the seeking.
One consequence of the Sahel drought was renewed interest in the nature and
causes of rainfall variability in both the Sahel-Sudan zone and the Horn of Africa.
Bell and Lamb (
2006
, p. 5343) described the severe Sahel-Sudan drought that began in
