Geoscience Reference
In-Depth Information
19.2
Climate, Climate Risks, and Climate Change
in sub-Saharan Africa
Climate in Africa is infl uenced by large-scale (synoptic) and small-scale (meso-scale)
systems. The main synoptic systems are (i) inter-tropical convergence zones (ITCZ),
(ii) extra tropical weather systems (sub-tropical high pressure systems), (iii) squall
lines, (iv) Easterly/Westerly wave perturbations, (v) jet stream, and (vi) tropical
cyclones. Other large-scale systems are monsoonal fl ows, teleconnections (global
scale climate anomalies associated with sea surface temperatures), Quasi Biennial
Oscillation (QBO), and El Niño/La Niña Southern Oscillation (ENSO). These clas-
sical climate patterns are further modifi ed in some areas by meso-scale features
such as mountains and large lakes which create small-scale circulation patterns that
interact with large-scale fl ow. These factors result in different climatic zones in
Africa, some of which are more disaster-prone than others.
East Africa in particular is under the infl uence of the El Niño Southern Oscillation
(ENSO). Warming and cooling of the central and eastern equatorial Pacifi c Ocean
region (El Niño and La Niña events) are associated with changes in atmospheric
pressure known as the Southern Oscillation (SO) and infl uence the atmosphere and
neighboring oceans in various ways. Since the SO is closely linked to El Niño epi-
sodes, they are collectively referred to as the ENSO. The ENSO event recurs every
2-7 years and usually lasts 6-12 months, although it sometimes can persist up to 24
months. For some locations on the globe, there is ample lead time once an El Niño
or La Niña has begun to take effective action to prepare for it (Glantz 2000 ).
El Niño and La Niña events correlate strongly with seasonal rainfall anomalies
in the East Africa region. In general, rainfall occurs during the onset of the warm/
cold ENSO events (Indeje et al. 2000 ). Severe droughts and fl oods, such as the
1997/98 El Niño-related fl oods followed by the 1998/2000 El Niño-related droughts,
provide a good illustration of the disasters associated with the ENSO events in SSA
(Glantz et al. 1997 ). Some of the consequences of droughts, and institutional
responses to droughts, are further described in Chap. 11 .
As described in Chap. 2 , the occurrence of climate extremes is likely to increase
in the future. This is especially true in the Greater Horn of Africa. Although the
impacts of climate change are not precisely foreseeable, especially at the local level
(UNECA 2011 ), studies have indicated that the following could occur in SSA this
century: increased hydrological stresses (expected by 2020); increased and increas-
ingly rising temperatures; extreme events (storms, dry spells, etc.); gradual changes
in precipitation, with increased rainfall variability; and a worsening of coastal ero-
sion associated with sea level rise (Stern 2006 ; IPCC 2007 ; UNECA 2011 ).
Some of these impacts may even be already felt and have been experienced in
the past. Researchers have pointed out possible links between climate change and
hazards in East Africa ranging from wetter conditions (McSweeney and Jones
2012 ; Vecchi and Soden 2007 ) to drying movements (Funk and Verdin 2009 ).
A recent study showed that anthropogenic climate change played a role in climate
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