Programme OS1f Africa
Ecosystem services and the variability of Lake Chad during a drought
Author(s): Jacques Lemoalle(1), Jean-Claude Bader(1), Marc Leblanc(2)
(1).- IRD-MSE, BP 64501, 34394 Montpellier cedex 5, France
tel 33 (0)4
6714 9027 ; fax 33(0)4 6714 9071 ; email@example.com
(2).- James Cook Univ., Australia
Keyword(s): Lake Chad, Africa, model,
Session: OS1f Africa
As in most of
West and Central Africa, the rainfall regime over the Lake Chad basin has changed around 1970 from a humid to a
dry period. Lake Chad being a closed lake, its surface area has changed according to the lower water inputs from
the watershed. The lake, which covered about 22000 km2 in the 1960s, is now divided into different individual
seasonal or perennial lake basins.
In the northern basin of the lake, the seasonally inundated area has varied
from zero in dry years (as in 1985, 1987, 1988) to 6000 km2 (1979, 1989, 2000 and 2001). In the southern basin
of the lake, the between year variability has markedly decreased.
The changes in lake area and in the links
between the lake basins have been modelled as a function of the river inputs. Satellite estimates of water area in the
northern basin and gauge levels in the southern basin have been used as calibration data. The water volumes
incorporated in and lost by the sediments during the annual wet and dry cycle have been taken into account in the
The hydrologic changes are the driving forces for the natural resources associated with the lake i.e.
fisheries, recession cultivation on the lake floor and green vegetation for livestock. Whereas the yearly cycle of the
natural resources has become fairly predictable in the southern basin, vulnerability has much increased in the northern
Field observations and the model are used to discuss the benefits and drawbacks of the present
situation compared with the wet period before 1970, and in the hypothesis of climate change. The possible impact of
the planned inter-basin transfers from the Congo-Zaire basin is also analyzed.