Groundwater; an untapped resource?

💧What is groundwater 



This video provides an introductory insight into the topic discussed in the blog. 

Michelle Williams the Dean of the faculty at the Harvard TH Chan School of Public health wrote an emotive piece for the Financial Times with the crisis narrative around climate change as one of the main themes to Africa’s food and water security article. One of the solutions she proposes which she believes has not been utilised effectively is groundwater.

"Expanding that (Amount of groundwater used) and investing in desalination plants could strengthen the region’s resilience against droughts and other climate shocks; most countries in Africa have enough groundwater to last decades, even if rainfalls diminish”.

Figure 1: Tweet from the BGS on groundwater


The tweet above evokes the same message as the article yet groundwater is being perceived as the solution to drought, however the complexities of groundwater means that whilst there are groundwater reserves in African countries I argue 50 years worth of water is a false statement as sole use of this resource can lead to the same consequences of the green revolution in Asia (John and Babu, 2021). Whilst 1% of the cultivated land in Africa is irrigated using groundwater with 80% being in North Africa, the extraction process of groundwater change the aquifer once overexploitation occurs and alters the water table (Siebert et al., 2010) .

Lets debunk that last statement by Michelle on most countries in Africa having enough groundwater to last decades.

1)      Different depth groundwater storages

No two groundwater aquifers are the same and here depth and geology play a key role in the accessibility of the resource. Differing geologies for example sedimentary basins which are commonly found in north Africa have the depth of 50m with weathered crystalline rock found in areas of equatorial Africa. These varying depths and differing geologies means the extraction process will look very different depending on the aquifer (Taylor et al., 2019). The amount of water also differs based on these factors as crystalline basement rock tend to contain the least amount of storage (Nanteza et al., 2016). A small storage of groundwater usually leads to small community handpumps for small scale irrigation plots or for domestic use but are unsuitable for large amounts of extraction. The infrastructure required for small volume aquifers are much smaller scale compared to large groundwater storages which are much deeper and usually much more difficult to access. This will require specialist drilling equipment which increases the cost of exploiting these resources (Alan et al., 2013).

2)      Recharge rates

Again no two groundwater aquifers have the exact same recharge rates. Previous studies highlight how many African countries with low recharge rates possess substantial groundwater storage whereas aquifers with low storage experience a high as well as regular recharge (Edmunds, 2012). This brings the question of sustainability into the matter. Is it sustainable to extract groundwater when it is known the groundwater resource took around 5000 years to recharge? The simple answer is no, this is not sustainable. However with issues of extended dry seasons due to climate change this may be an attractive solution for politicians in the short term.

Figure 2: Source (McDonald, 2021)


Figure 2 highlights the long term average of groundwater recharge. This particular study highlights the spatial differentiations of groundwater recharge in the African continent. From the graph it is evident that recharge is not detected in major sites in parts of north and south Africa (red dots). Semi-arid and arid regions have some source of groundwater recharge although this did not occur on an annual basis whilst in the sub-humid and humid regions recharge was occurring annually.

Whilst mapping is useful in visualising the recharge rates based on region, it requires on the ground data collection and with groundwater changing and being influenced by factors such as pollution, contamination, over-extraction, recharge data needs to be collected over a long period of time which can prove to be a challenge for funding extensive (Edmunds, 2012).

Returning back to the FT article yes, the statistics paint a simplistic picture; if there is an ample amount of groundwater aquifers in the African continent why is the resource not exploited? However, the statistics show one side of the story with an estimate of how much groundwater is in Africa, without highlighting the complexities of groundwater extraction, geology, depth, recharge and social factors to do with contamination, infrastructure which are playing a significant role in the management of this resource.

Solutions

One of the solutions to groundwater management is long term research into the groundwater aquifers. Analysing the changes in aquifers based on extraction and recharge can help make informed decisions on estimating how much extraction of the resource can be possible without undermining sustainability. Projects such as UPGro have been working on building the scientific knowledge of African groundwater storage and working with communities who will ultimately be using the resource. The aim was to recognise that different areas may have different uses and requirements for groundwater and being able to provide communities with different scenarios and options for future extraction allows them to make the decisions based on their current and future needs. The ultimate goal is to not have a repeat of the green revolution in Asia where groundwater was used in an unsustainable manner which lead to unhealthy aquifers and left the agricultural economy reliant on groundwater for irrigation.

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