What Good is Groundwater?

In an earlier post, I mentioned that the water crisis in Africa is complex and somewhat misunderstood. A common misconception is that there are insufficient water resources on the African continent to sustain its vast population. In fact, maps published in a paper by MacDonald et al. (2012) suggest the opposite. Their research reveals that groundwater reserves across Africa are more than 100 times the annual renewable freshwater resources. The extensive aquifer systems beneath the continent hold approximately 0.66 million km3 of freshwater. Looking back to my post on the current drought in South Africa, I explained how the Western Cape is suffering from the worst drought in over a century due to the El Nino. MacDonald et al (2012) say that South Africa has more freshwater in groundwater stores than approximately two-thirds of other African countries. There is no doubt that the extraction of this groundwater has the potential to overcome the water crisis. 

Figure 1: Groundwater storage across Africa (MacDonald et al., 2012)

At present, 80% of the food grown in Africa relies on surface waters, and less than 5% of global freshwater withdrawals go to Africa for agricultural purposes. Water withdrawals in Africa are focussed in Northern Africa and some around the coast of East Africa and Madagascar. Most of West and Central Africa relies on surface and rainwater.  It is the dependence upon rain fed agriculture in Sub-Saharan Africa that leaves many regions vulnerable to drought. As groundwater is protected from evapotranspiration, it is superior to surface water in hot climates such as in Africa. As well as its resistance to evapotranspiration, groundwater would be a better solution to the African water crisis than surface water as it is also less susceptible to contamination, overcoming the sanitation issues associated with drinking water in Africa. Surface waters such as streams are at high risk of contamination from human and bird waste, transport fume, and agricultural runoff such as pesticides. Being in the subsurface, water held in aquifers is largely protected from such contamination. What’s more, groundwater undergoes filtration as it travels through rocks.

However, it is never just that simple. For starters, there are issues over who should have access to the groundwater. An estimated 80 aquifers across the Africa fall into the boundaries of more than one country. If one country were to begin pumping heavily from an aquifer system that is shared with others, this could lead to even more political unrest than what currently exists. Furthermore, there is the issue of whether or not the groundwater can be accessed. A paper by Giordano (2006) outlines the distinct geological zones across SSA. Approximately 40% of the region is Crystalline Basement Rock, which has low transmissivity and so it a poor supply source of groundwater. Hence, groundwater is not a solution to drought and resultant food supply issues in all regions.

To summarise, groundwater has the potential to overcome the challenge of drought across Africa, and the associated food crisis. In the areas where extraction is possible, the freshwater in aquifers could be used to increase the percentage of land under irrigation across the continent, and increase both water and food security during times of drought. So as not to deplete the resource, aquifer pumping should only be done when the use of surface water is not viable- over-abstraction can also lead to land subsidence and saline intrusion (Ogunba, 2012). This solution would require agreements amongst stakeholders i.e. agreements between the countries whose boundaries lie above the aquifers.