The variability and uncertainty of Africa’s water supplies.

Africa’s water supplies are amongst the most varied globally. Current estimates suggest the water availability exceeds Europe but the challenges of distribution and variability make it more complicated than one may first think.

The distribution of water is strongly controlled by tectonics. Rifting, for example the formation of the East African Rift System (EARS), influences drainage (Beadle: 1974) and thus affects the hydroclimatiology in the area. As a result, river flow is altered which has an effect on the surface water available.

Precipitation variations is another cause of water variability. Across Africa the Inter- Tropical Convergence Zone (ITCZ) determines the seasonality in precipitation.  Precipitation corresponds with the position of the ITCZ. As can be seen below, the ITCZ moves. Countries that lie between the two red lines get rainfall throughout the year, but those that lie on the periphery such as the Sahara desert, receive very little rainfall. West Africa and Tropical extremes experience unimodal precipitation whilst Tropical east Africa experiences a bimodal pattern. Aside from the annual shifts, climate change also causes variations in precipitation. It is expected to cause less frequent but more extreme rainfall events and sometimes rains do not come when expected. This emphasises not only the spatial variability but the temporal uncertainty too. Studies carried out by Conway et al (2009) show there are no consistent rainfall and river flow patterns across the region. The rainfall largely controls river flow and thus surface water availability.

            Figure 1: The movement of the ITCZ across Africa (Ziegler et al (2013))                                                                                     

This has profound impacts for water availability and use. As small as a 10% reduction in precipitation can cause up to a 50% reduction in river discharge (de Wit andStankiewicz: 2006). Since climate change is increasingly unreliable, we have to develop other sources which are less temperamental.

As can be seen, the climate and tectonics of Africa mean the water availability comes with extreme uncertainty and variability. The next post will consider how groundwater can be used as a solution to these issues. Africa is unique in that it has a sparse distribution of small hold farmers. Could groundwater be agriculture’s answer to providing water across Africa to all these farmers?

References

Beadle, L.C., 1974. The inland waters of tropical Africa. Longman, USA: Prentice Hall Press.

Conway, D. et al., (2009), “Rainfall and water resources variability in sub- Saharan Africa during the 20^th Century.”, Journal of Hydrometeorology, 10, 41-59.

deWit, M. and Stankiewicz, J., (2006), “Change in surface water supply across Africa with predicted Climate Change.”, Science, 311, 1917- 1921.

Figure reference

Ziegler, M. et al., (2013), “Development of Middle Stone Age innovation linked to Rapid Climate Change.”, Nature Communication, 4: 1905, 1-9.