Climate Change and Groundwater: Looking to the Future (Part 2)

 Following on from the previous post discussing the distribution of groundwater resources across the African continent, specifically highlighting it as potential resource for climate change resilience, the potential limits and opportunities will now be analysed.

The primary issue is a geological and geographic constraint that not all of the groundwater is available for extraction or it is not feasible to extract in a practical manner (Calow et al, 2009). This is often due to shallow groundwater or very deep water table surface that requires large scale engineering power, as seen with the infrastructure across the Nubian aquifer system as the depth to the groundwater varies between 70-200m (Hamdan & Sawires, 2013). This is also shown in figure 2, particularly highlighting the large depth to groundwater in sub-saharan Africa and the shallow groundwater depth for large parts of central and southern Africa. If these geographical and geological issues can be overcome through innovative engineering and correct financing, the availability of the groundwater resource, particularly for sub-saharan Africa will likely have positive benefits, although this is dependent on correct management with knowledge of the groundwater systems that will differ within local regions. 

The best example of this is differences in groundwater recharge rates within the Nubian sandstone aquifer, as this is largely dependent on climate and geology. Basement outcrops in Egypt prevent even recharge across the aquifer leading to increased pressure on groundwater supplies in Egypt compared to Libya and Tunisia where the groundwater recharge is not impeded by geological features, therefore storage and groundwater levels are more stable (Mohamed at al, 2016). Understanding how precipitation and geology determines the rates of aquifer replenishment is crucial to provide adequate climate resilience and buffers for these communities during periods of local drought. The same aquifer system will experience local differences in recharge rates, with some areas highly dependent on sporadic and episodic precipitation and others reliant on groundwater being transported from other regions with relatively consistent precipitation patterns. These patterns are evident in Tanzania where episodic precipitation ensures sufficient groundwater recharge thereby ensuring water security for the local communities (Taylor et al, 2012). Due to the geological impediments in the Nubian aquifer, Ethiopia and Egypt are heavily reliant on sporadic downpours for groundwater replenishment whereas Libya and Tunisia can rely on the consistent rainfall in the Sudanese highlands to be transported into the aquifer (Cuthbert et al, 2019). The reliance on sporadic downpours for recharge is not likely to provide adequate resilience to long term climate change for water scarce regions, especially without sufficient aquifer management and international cooperation.

As mentioned, improper groundwater management is another obstacle to using groundwater as a resource for climate resilience to combat water scarcity. Improper management is caused by excessive exploitation, groundwater salinisation due to improper systems and groundwater pollution (Foster & Chilton, 2003). Whilst groundwater is an abundant resource, it is also extremely vulnerable to excessive extraction due to uneven and sporadic nature of recharge. The specific problem of excessive extraction can result in shortages during periods of high demand, however more extreme consequences such as saline intrusion in coastal areas are also possible. This is a reoccurring problem in the Nile Delta where saltwater intrusion into the sand and gravel aquifer is not prevented due to the lack of groundwater recharge, particularly during the summer months (Nofal et al, 2015). 

Figure 1: Diagram showing how saline intrusion occurs between there freshwater and saline interface. The 'h' and 'z' values reflect the relative heights that will change when the groundwater head is altered. The change in 'z' is given by the Gyhben Herzberg equation is highly non linear and can be found at this link.

Since saltwater intrusion is highly non-linear, small changes in groundwater head will result in roughly 40 times larger increases in saltwater intrusion, therefore effective management through accurate monitoring and prevention schemes is vital in order to prevent water scarcity and effectively use groundwater as a resource (Abd-Elaty, 2018). 

If the above variables and factors are well dealt with to prevent any negative consequences of groundwater exploitation, aquifers can provide a strong buffer to mitigate water scarcity in the region and effectively counter the hydrological problems associated with accelerated climate change.