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).
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| 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.
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| 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).
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| 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.
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| 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.
