Changes in Surface Water

Source

Based on previous blog posts, it should now be clear that the planet is warming and this is having a significant effect on precipitation and evapotranspiration rates. Although warming in the near future is guaranteed (see Fifth Assessment Reportof the Intergovernmental Panel on Climate Change), there is uncertainty in how warming an changes in precipitation will affect freshwater availability (Taylor et al 2009).

Africa’s rainfall variability is very, with 95% of Africa’s annual rainfall deviating by 20-40% from the mean (Carter and Parker 2009). This precipitation variation is high both seasonally and interannually, which has a considerable effect on river discharge (Mahé 2009). McMahon et al (2007) found that southern Africa has the greatest median coefficient of variation at 82% out of anywhere in the world, with the global median coefficient of variation paling in comparison at 31%. High rainfall and discharge variability will potentially have devastating implications for Africa’s 1.2 billion people, where lots of the populations water supply is reliant on local streams.

De Wit and Stankiewicz (2006) wrote an article that discussed how changes in surface water supply would occur as a result of climate change. They identified three climate regions in Africa: the dry regime receiving less than 400mm year ^-1 of precipitation; the intermediate regime receiving over 400mm year ^-1 of precipitation and the upper regime receiving over 1000mm year ^-1 of precipitation. It was found that areas in the dry regime had no perennial drainage, in the intermediate regime drainage then increased with increasing precipitation and then decreased once precipitation exceeded the threshold of 1000mm per year. This nonlinear response of drainage to rainfall had the most significant effect on the intermediate regime, where a 10% decrease in precipitation would reduce drainage by 50%. Considering that 75% of African countries fall into the unstable, intermediate regime, it can be said that a reduction in precipitation would significant reduce surface water supply for much of Africa.

One of the regions expected to be most severely threatened is southern Africa. Most of southern Africa lies in the unstable regime, with some areas falling in the dry, arid regime. Southern Africa is expected to experience considerable reductions in its already limited drainage, posing huge problems for the region in terms of drought relief. The densely populated areas around Cape Town are likely to be hit hard, with estimations of a loss of more than half of their perennial supply. This poses a huge threat to poverty eradication in southern Africa as humans are dependent on rivers for food, water and their livelihoods, with water often directly linked to economic development (Postel and Mastel 2005). 

This paper serves as a useful foundation in which African governments can begin to manage surface water resources in response to the threats from climate change. Perhaps the categorisation of Africa into only three regimes is an oversimplification of the issue, but this still provides the opportunity for academics and/or water management agencies to conduct more localised studies on areas of interests to further expand upon the results in this paper.