10.2. Key Regional Concerns
10.2.1. Water Resources
10.2.1.1 Overview of Regional Water Resources
Water resources are inextricably linked with climate, so the prospect of global
climate change has serious implications for water resources and regional development
(Riebsame et al., 1995). Efforts to provide adequate water resources for
Africa will confront several challenges, including population pressure; problems
associated with land use, such as erosion/siltation; and possible ecological consequences
of land-use change on the hydrological cycle. Climate changeespecially changes
in climate variability through droughts and floodingwill make addressing
these problems more complex. The greatest impact will continue to be felt by the
poor, who have the most limited access to water resources.
Figure 10-4 shows that the hydrological performance of
Africa results in much less runoff yield than in other regions. Apart from the
Zambezi/Congo Rivers, the major African rivers (Nile, Niger, Senegal, Senqu/Orange,
Rufiji) traverse semi-arid to arid lands on their way to the coast. Of the world's
major rivers, the Nile has the lowest specific discharge (i.e., flow per unit
catchment area), even if only the part of the catchment that receives precipitation
is considered (Reibsame et al., 1995). Furthermore, because these major
rivers originate within the tropics, where temperatures are high, evaporative
losses also are high in comparison to rivers in temperate regions. Elevated
temperatures will enhance evaporative losses; unless they are compensated by
increased precipitation, runoff is likely to be further reduced.
In Morocco, the northward displacement of the Azores high-pressure cell is
a subject of study because of its asscociation with a drought cycle that is
related to the dipole between the positioning of the Azores high-pressure cell
and the Iceland low-pressure cell. These severe droughts seem to manifest themselves
in Morocco in periodicities varying between 2 and 13 years (Stockton and Allali,
The Magreb region is characterized by erratic and variable rainfall, with a
high rate of evapotranspiration (almost 80%). In addition, the Magreb region
will have water scarcity by 2025, especially in Tunisia and Libya.
Associated with the poor hydrological performance of African river basins is
the fact that most of the lakes in Africa have a delicate balance between precipitation
and runoff; all of the large lakes show less than 10% runoff-to-precipitation
ratio (Talling and Lemoalle, 1998), and important water basins like Lake Chad
and the Okavango Delta have no outflow because evaporation and permiation balance
runoff (see Figure 10-5).
In the savanna regions, the incidence of seasonal flow cessation may be on
the increase, as shown by some streams in Zimbabwe (Magadza, 2000). Drought
periods now translate into critical water shortages for industrial and urban
domestic supplies (Magadza, 1996).
Figure 10-3: Observed annual rainfall anomalies for three African
regions, 1900-1998, and model-simulated anomalies for 2000-2099.
Model anomalies are for 10 model simulations derived from seven DDC GCM
experiments; the four HadCM2 simulations are the dashed curves. All anomalies
are expressed with respect to observed or model-simulated 1961-1990
average rainfall. Model curves are extracted directly from GCM experiments,
and results are not scaled to SRES scenarios used in Chapter
3. Smooth curves result from applying a 20-year Gaussian filter (Hulme
et al., 2001).
Figure 10-4: Comparative hydrology in world regionstotal
runoff as percentage of precipitation (GEMS, 1995).
Figure 10-5: Evaporative losses as percentage of total hydrological
income in selected African lakes (constructed from Talling and Lemoalle,