Having provided some background on existing sensitivities/ vulnerabilities generated by a range of factors, including climate stress, some of the impacts and vulnerabilities that may arise under a changing climate in Africa, using the various scenarios and model projections as guides, are presented for various sectors. Note that several authors (e.g., Agoumi, 2003; Legesse et al., 2003; Conway, 2005, Thornton et al., 2006) warn against the over-interpretation of results, owing to the limitations of some of the projections and models used. For other assessments see also Biggs et al. (2004), Muriuki et al. (2005) and Nkomo et al. (2006).
Climate change and variability have the potential to impose additional pressures on water availability, water accessibility and water demand in Africa. Even in the absence of climate change (see Section 9.2.2), present population trends and patterns of water use indicate that more African countries will exceed the limits of their "economically usable, land-based water resources before 2025" (Ashton, 2002, p. 236). In some assessments, the population at risk of increased water stress in Africa, for the full range of SRES scenarios, is projected to be 75-250 million and 350-600 million people by the 2020s and 2050s, respectively (Arnell, 2004). However, the impact of climate change on water resources across the continent is not uniform. An analysis of six climate models (HadCM3, ECHAM4-OPYC, CSIRO-Mk2, CGCM2, GFDL_r30 and CCSR/NIES2) and the SRES scenarios (Arnell, 2004) shows a likely increase in the number of people who could experience water stress by 2055 in northern and southern Africa (Figure 9.3). In contrast, more people in eastern and western Africa will be likely to experience a reduction rather than an increase in water stress (Arnell, 2006a).
Clearly these estimations are at macro-scales and may mask a range of complex hydrological interactions and local-scale differences (for other assessments on southern Africa, where some of these interacting scalar issues have been addressed, see Schulze et al., 2001). Detailed assessments in northern Africa based on temperature increases of 1-4°C and reductions in precipitation of between 0 and 10% show that the Ouergha watershed in Morocco is likely to undergo changes for the period 2000-2020. A 1°C increase in temperature could change runoff by of the order of 10%, assuming that the precipitation levels remain constant. If such an annual decrease in runoff were to occur in other watersheds, the impacts in such areas could be equivalent to the loss of one large dam per year (Agoumi, 2003). Further interactions between climate and other factors influencing water resources have also been well highlighted for Egypt (Box 9.2).
Northern Africa: 2055
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