Groundwater Resources in Africa

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This interview featuring Richard Taylor popped up on my twitter feed the other day, and of course I had to check it out. 


In the interview he mentions that he’s working “identifying a bias in the replenishment of groundwater in the tropics to heavy rainfalls. As global warming leads to fewer but heavier precipitation events… this discovery has profound implications for the use of groundwater as a sustainable adaptation strategy to climate change in low-income countries of the tropics.”


So what does he mean by that? Since I covered surface water patterns and trends of the continent in a previous post, it will believe it will beneficial to also examine the spatial patterns of groundwater storage and how it may potentially change under environmental change.



Groundwater Distribution in Africa

It is estimated that the average decadal recharge in the continent is 15,000 km3 (4900 - 45,000 km3), however the distribution of groundwater across the continent is highly uneven, as shown in Figure 1 (MacDonald et al. 2021). The location of aquifers and its water storage is dependent on many variables including precipitation (controlling recharge), geology (controlling infiltration and storage), topography (controlling discharge), and temperature (controlling evapotranspiration). In addition to that, there are other environmental controls and feedback from land cover type and human activity. 


There is a huge underground store beyond 50,000 mm in depth in arid Northern Africa, crossing over political boundaries of countries such as Algeria, Libya, Egypt and Sudan. This is due to the sedimentary sandstone in the area that creates a great condition for subsurface water storage despite having low levels of rainfall and recharge. On the other hand there is also a substantial aquifer underneath the tropical Democratic Republic of the Congo, where it gets high precipitation rates and high annual recharge but weathered crystalline-rock with lower capacity for storage (MacDonald et al. 2021). 


Figure 1. Estimated groundwater storage in Africa (Macdonald et al. 2012)


Environmental Change Effects

As mentioned in my previous post, as climate change continues, Africa will experience more variability including spatially and temporally changing precipitation patterns as well as its intensity. This will affect recharge processes across the continent and change the amount stored as well as where it is stored, the uncertainty making it more difficult to estimate the exact effects of climate change on groundwater.


Taylor et al. 2012 found that aquifer recharge is tightly linked to intense episodic precipitation, implying that groundwater recharge is more sensitive to the intensity of rainfall instead of the overall volume of rainfall. In addition, levels of aridity dictate the predominant recharge processes while local hydrogeology influences the type and sensitivity of precipitation-recharge relationships. Recharge in humid locations varies by as little by 5% over the wide range of values due to potentially saturation or runoff, on the other hand arid regions show roughly linear precipitation-recharge relationships, and these tend to rise as aridity increases, making groundwater recharge ‘flashier’ and more episodic (Cuthbert et al. 2019). 


Therefore, under the assumption that there will be more frequent and heavy rainfall events, there may be greater rates of groundwater recharge, especially in semi-arid areas which have higher precipitation-recharge relationships and are more sensitive to recharge (Carter and Parker, 2009).


Groundwater as a ‘Buffer’

There are some contrasting views in literature about the ability of groundwater resources to act as a ‘buffer’ and increase climate resilience, and whether it can sustainably fulfil demand. As seen above, groundwater resources are abundant particularly in areas that may be suffering water scarcity (Northern Africa). This provides a huge opportunity for infrastructure to be implemented to tap into that water resource. In fact, the majority of domestic water supply in sub-Saharan Africa comes from groundwater. 


There is a growing consensus amongst academics that groundwater reserves in sub-Saharan Africa are more resilient to climate change than surface water as it has a slower response to changing climate conditions. Unfortunately, available and accurate monitoring and data on groundwater recharge is sparse across the continent, making it difficult to create models and inform decision makers. 


There are also a large variety of factors that need to be considered before implementing plans on groundwater usage. This includes human activities such as deforestation, urbanisation, and unplanned irrigation, as all of these

processes can change the rate and location of recharge. In addition, Africa’s population is increasing rapidly, with projections stating that by 2050, the urban population will increase by four times and the rural population will increase by 45%. All of this will lead to a massive, concentrated increase in the demand for water (Carter and Parker, 2009). Without proper management, groundwater can easily be over-exploited as it can essentially be non-renewable, especially in arid and semi-arid areas where recharge is low. Another case that should be considered along coastal regions is the possibility of saltwater intrusion, potentially due to sea-level rise brought on by climate change, but also over-exploitation causing the water table to rise.


Like any resource, there is plenty to consider before implementing long-term, large-scale plans on how groundwater, a natural system, can be managed and exploited to support its communities in a sustainable manner.

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