Africa and the Limitations to Groundwater: Fool's Gold?

Groundwater has become quite the big player in agriculture over the last couple of decades, especially in the developing world. South Asia are huge fans, with ground water supplying over half of their irrigation projects, and China is no stranger to the rather shy resource, with it supplying 30% of irrigation in North China’s grain belts. Groundwater has lifted millions out of hunger and poverty, and driven food prices down into the ground. Undeniably, a “Green Revolution” has taken the world by storm – that is, everywhere except for Africa (Giordano 2006).

Irrigated Agriculture in China

At first glance this seems confusing; why is Africa, a continent with substantial groundwater resources and temperamental at best food security the only major region in the world within which food production per capita has actually fallen over the last 30 years? Surely, Africa, which sits on a veritable ocean of groundwater, should be leading the charge into mass agriculture and food security?

As usual, this is a complex scenario, and a complex set of constraints prevent groundwater from becoming the cure-all for African agriculture. These are explored thoroughly by Giordano (2006), and stretch from variability in distribution, the make-up of social landscapes and issues of cost and infrastructure.

One of the main reasons groundwater is difficult to harness in Africa is because of its distribution, which, in an absolutely stunning turn of events, is highly variable. In fact, distribution tends to be at the mercy of geology, and depends largely on the capacity of underlying rock to store and transfer the precious liquid. Giordano identifies four general hydrogeological zones in Sub-Saharan Africa, which, although very simplistic, paint a good picture of why groundwater is found in some places, and not in others. These jolly zones consist of;

1.     ---  Crystalline basement rock, which contains groundwater in its weathered mantle and fracture zones. This bad-boy makes up around 40% of Sub-Saharan Africa; however its use as a general water source is limited by its low transmissivity. It does however show potential for domestic use (which is minimal) and for livestock

2.    ---  Next up is consolidated sedimentary rock, making up 32% of Sub-Saharan Africa. This serves as a great store for groundwater, and takes the form mostly of highly porous limestones and sandstones and some less desirable mudstone areas which store little

3.    --- In the red corner we have unconsolidated sediments, making up 22%. These hold groundwater, often in river beds, however extraction is made difficult by fine and very fine sediments

4.    --- Last but not least Giordano identifies the volcanic rock geological zone, making up 6%. These cover a relatively small area, but can hold large amounts of groundwater in palesols and fractures.

 

A Fifth (but not relevant) Example of Bedrock

 

As you’d expect, these hydrogeological zones don’t make up anything like a neat patchwork. Rather, Africa, and Sub-Saharan Africa especially, are a complete mismatch of zones. Consequently, some areas are geared for groundwater, whilst others are left in the dry.

Climate also plays a large role in groundwater availability. Groundwater sources in arid areas are dependent on recharge to be sustainable and consistent, and this is becoming ever rarer. On the other hand, in humid regions, groundwater exists in abundance and is readily recharged. It seems like twisted irony that the areas with the highest mean rainfall also have the most groundwater, which is often rarely used. Much of Africa’s groundwater is also what’s known as “fossil water”, non-renewable sources from ages gone by. These are usually at significant depth and out of reach of the average Joe.

It is clear then that the physical affects of geology and climate massively effect groundwater availability. In overly simple (and very broad-brush) terms, there's either not enough there, you don't really need it or it IS there but you can't get at it because it's too hard to pump or you need a huge industrial drill (not readily available to the general public).

 

Estimated Depth to Groundwater from the British Geological Survey --- as you can see, areas with the most accessible groundwater also appear to be the areas that recieve the most rain from the ITCZ

Fear not, however, because social limitations also abound (Giordano 2006). In fact, it is the relationship between human and physical attributes in Sub-Saharan and much of Continental Africa that is one of the main barriers to agricultural use of groundwater. Arguably one of the most considerable, and touched upon earlier, is that the areas with the highest groundwater levels are also those that receive more than sufficient rainfall; this makes groundwater usage seem somewhat unnecessary. On top of this, Africa’s position as land-abundant and people sparse (when compared to much of the developing world), actively discourages groundwater irrigation; farms tend to be small in size due to insufficient labour, which makes rain-fed agriculture far more cost-effective than expensive irrigation schemes.

In fact, groundwater irrigation typically only occurs in areas undergoing agricultural intensification, prerequisites of which are population growth and market development; conditions unfortunately only seen in small pockets of Sub-Saharan and much of the rest of Africa.

Development costs of irrigation also tend to be far higher in Africa than in other parts of the world. Groundwater typically exists in fractures; these are vertical cracks in the bedrock which are often hard (and very expensive) to locate. This means boreholes are a risky business, and more often than not turn up empty handed. Yields, due to geology (such as low-transmissivity rocks and fine, congealed sediments), can also be disappointingly low, making it far more expensive to extract the same amount of water in Africa than in Asia or other regions. And, just as one (not quite) final slap in the face, the areas that ARE suitable for exploitation are often far from markets, meaning there is little economic drive to develop the resource. ON TOP of this, you have issues such as poor infrastructure, manufacturing capacity and a lack of capital availability.

AND just in case you thought there was even a scrap of hope, large-scale irrigation projects can also attract large amounts of animosity from local farmers, who may feel their land rights are being taken away. They are controversial indeed.

A Rainwater Harvesting Tank, Uganda

Although rather critical towards usage of groundwater, Giordano does put forward a convincing and thorough argument as to why Africa has had to forego the “Green Revolution”. It appears that groundwater, for many agricultural areas and practices, is simply unsuitable. It is a resource that requires large-scale manipulation but makes its home in a continent that thrives on small-scale and community-level agricultural projects. Although there are some small-holder farms that take advantage of the hidden resource, they are few and far between, with groundwater agriculture supporting only around 1% of the population.  Africa will require a real boost in intensification and trade opportunities before it has the resources, utility and motivation to harness groundwater on an industrial scale for agriculture. Until then, it is safe to assume that rain-fed agriculture will remain dominant across the continent.