GEO-6 Regional Assessment for Africa


Water level (m)


mainly used for hydropower such as Kariba, where the water level dropped by 11.6 metres between 1981 and 1992 due to a series of droughts (SARDC and HBS 2010), resulting in reduced capacity to generate electricity (SARDC et al. 2012). Kling et al. (2014) reported that, based on modelling of the hydrological impact of water resource development and climate change scenarios on discharge conditions in the Zambezi basin, there is a decline in water levels in the major dams (Kariba and Cahora Bossa), which could affect water availability for irrigation and hydropower. Lake Victoria’s water levels (Figure 2.3.3) have also been observed to be sensitive to climatic factors, with a declining trend recorded between 2003 and 2007 (Awange et al. 2008).


Over-abstraction to meet the needs of a growing population is blamed for the drying up of Lake Haromaya in Ethiopia at the end of 2005 (Figure 2.3.4), the main cause being rising demand for irrigation.


Figure 2.3.3: Annual water-level variations in Lake Victoria 2.0


1.5 1.0


0.5 0.0 -0.5 -1.0


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1.5 1.0


0.5 0.0 -0.5 -1.0


TOPEX/Poseidon historical archive


Figure 2.3.4: Declining water levels in Lake Haromaya, Ethiopia, 1975–2005


10


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Year Source: Alemayehu et al. 2007


2.3.3 Availability and distribution The main source of water for surface and groundwater storage is rainfall. Rainfall amounts are highly variable across Africa, from negligible over arid parts of the continent to very high in tropical countries. As a consequence, Africa’s hydrology shows great variability in evaporation and stream discharge. The long dry season of more than five months over much of Africa increases reliance on groundwater storage (MacDonald et al. 2009).


More than 1 270 dams have been built on African rivers to store and supply water for hydropower and irrigation (UNEP 2008). Most of the supply dams are in North, West and Southern African countries (Figure 2.3.5), and are for the purpose of domestic water supply for large settlements, agriculture and hydropower generation (More...15).


Source: USDA 2015 62


Ahmed et al. (2014) revealed that large sections of Africa are undergoing significant variations in the total amount of water stored on land after precipitation has fallen as rain or accumulated as snow, filtered into the ground, or evaporated or departed from a basin as stream flow, with quantities ranging from more than 44 millimetres per year to less than 15 millimetres per year due to both natural and anthropogenic causes (Figures 2.3.6 and 2.3.7). Specific causes and variations include:


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2001 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016


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