Groundwater is a relatively abundant resource across
sub-Saharan Africa that is seldom used for irrigation, comprising of roughly 5% of
all withdrawals compared to 37% in Asia who recently experienced a ‘groundwater revolution’ (Siebert et al. 2010; Villholth 2013). Many
academics believe the substantial natural freshwater storage provides a viable
and reliable method of both meeting increased freshwater demand and partly
offsetting the ephemeral nature of surface water in rainfall-dependent areas (Adelana
and MacDonald 2008). With over 80% of domestic water usage in rural
sub-Saharan Africa derived from groundwater and the introduction of more
cost-effective pump and drilling solutions, it is considered by many as a
logical extension to the modus operandi of agriculture (Calow et al. 2010; Villholth 2013)
The potential of groundwater:
Villhoth and Altchenko (2016)
have determined that in recharge conditions of 70%, it could be expected that
the land area under irrigation could increase from 2 million to 40 million
hectares, a factorial increase of 20. Figure 1 shows a groundwater irrigation
potential map based upon: water availability, distance to surface water, distance
to market; soil suitability for agriculture; drilling and pumping cost: depth
of groundwater and access to electricity. It is clear the potential for
groundwater irrigation is substantial, most notably across the coast of western
Africa and central Africa. The uneven distribution of groundwater potential has
previously been highlighted by academics such as Giordano (2006) who explains
that countries such as Malawi and Ghana disproportionately utilise more groundwater
for irrigation than other countries in sub-Saharan region.
Rural small-hold farmers are the biggest area of growth for groundwater irrigation in rural areas, with small-scale groundwater irrigation estimated to cover 10 times as much land as publicly funded groundwater irrigation systems in some sub-Saharan countries (Villholth 2013). Villholth (2013) predicts this growth in small-scale groundwater irrigation will increase, especially in less arid nations such as Rwanda and Uganda. These small-scale schemes are shown to be more economically viable and provide higher rates of return than the notorious large-scale public schemes that often fail to target those most in need (Abric et al. 2011).
The dryland zones of sub-Saharan Africa cover approximately 40% of the regions land, 70% of cropland and 50% of the region’s population (Xie et al. 2018). Suffering with some of the most severe under-nutrition and increasing levels of food insecurity the area has been increasingly studied as a particular focus for groundwater irrigation development (Cervigni &Morris, 2016). Xie (et al. 2018) found that between 5-12 million hectares of the region could host sustainable and profitable small-scale irrigation (depending on capital cost). Their study predicts that small-scale irrigation would have the most significant impact in regard to food import dependency, predicting a decrease in net cereal imports of up to 90m tons and net vegetable imports of up to 40m tons. They also predicted that the population at risk of hunger could be reduced by up to 15 million people (Xie et al. 2018).
The constraints to a 'groundwater revolution':
It is also crucial to consider the renewability of groundwater resources to ensure their development is beneficial and sustainable in the long-term (Villhoth and Altchenko 2016). Estimations of extraction limits for the resource are important to enable sustainable agriculture, if the resource is over-exploited then catastrophe can strike. When reading a fellow students blog (Water and Food in Africa) I was intrigued by the concept of saline intrusion and how it can have serious long-term effects on agriculture. Saline intrusion is the contamination of freshwater aquifer with saltwater due to pressure differentials in the aquifer as a result of overuse and severely threatens the productivity of soil in coastal regions (Alfarrah and Walraevens 2018).
Final thoughts:
Whilst the potential for small-scale groundwater irrigation is high, the reality on the ground is extremely complex. With capital as one of the largest barriers to small-scale irrigation, micro-finance schemes and improved market access could help overcome financial constraints (WFN). While models such as that in Xie’s (et al. 2018) study and Figure 1 are useful, it is important to recognise that climate change will affect surface and groundwater resources available for farming. Thus groundwater irrigation potentials will change in accordance with resource availability and demand so continual monitoring of groundwater and crop yields is vital (Villhoth and Altchenko 2016). Before expanding groundwater irrigation, it is important that environmental flows are secured, and the use of groundwater is regulated in order to avoid overuse. With parts of sub-Saharan Africa already suffering from blue water scarcity it is important to plan expansion carefully taking into account future climate scenarios and socio-economic factors (WFN).
 |
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Figure 1. Maps
showing groundwater irrigation potential. Left: groundwater availability and
Right: area that could be irrigated (Villhoth
and Altchenko 2016).
|
Rural small-hold farmers are the biggest area of growth for groundwater irrigation in rural areas, with small-scale groundwater irrigation estimated to cover 10 times as much land as publicly funded groundwater irrigation systems in some sub-Saharan countries (Villholth 2013). Villholth (2013) predicts this growth in small-scale groundwater irrigation will increase, especially in less arid nations such as Rwanda and Uganda. These small-scale schemes are shown to be more economically viable and provide higher rates of return than the notorious large-scale public schemes that often fail to target those most in need (Abric et al. 2011).
The dryland zones of sub-Saharan Africa cover approximately 40% of the regions land, 70% of cropland and 50% of the region’s population (Xie et al. 2018). Suffering with some of the most severe under-nutrition and increasing levels of food insecurity the area has been increasingly studied as a particular focus for groundwater irrigation development (Cervigni &Morris, 2016). Xie (et al. 2018) found that between 5-12 million hectares of the region could host sustainable and profitable small-scale irrigation (depending on capital cost). Their study predicts that small-scale irrigation would have the most significant impact in regard to food import dependency, predicting a decrease in net cereal imports of up to 90m tons and net vegetable imports of up to 40m tons. They also predicted that the population at risk of hunger could be reduced by up to 15 million people (Xie et al. 2018).
The constraints to a 'groundwater revolution':
Small-scale irrigation is growing in an unplanned and
unregulated manner and faces several challenges (Giordano et al. 2012). Firstly,
when reviewing Figure 1 it is clear groundwater irrigation is not a region-wide
solution to irrigation demand and food insecurity. The heterogeneity of sub-Saharan Africa’s geological
and hydrological conditions influences the availability of groundwater and thus
ease of extraction, while demand is also geographically variable (Adelana
and MacDonald 2008; Villhoth and Altchenko 2016). The
hydrogeology and depth of groundwater are both factors that determine
suitability for irrigation, with hard rock types and deeper aquifers requiring
higher abstraction costs and specialist consultancy and a lacking water table
such as in Kenya meaning limited water resources are available for extraction.
Despite reduced costs, capital constraints are suggested to be the largest
barrier to groundwater irrigation for smallholders (see Figure 2) (Villholth 2013). Groundwater
irrigation’s potential as a method of poverty reduction has come into question
as often it is only the wealthiest smallholders that can afford the price of tools for drilling boreholes, pumping
water and the price to run and maintain pumps, potentially increasing
inequality between small hold farmers in sub-Saharan Africa. Some studies have
also suggested that in order to compensate for the expensive infrastructural
investment, smallholders will make the switch to high-value export crops as
opposed to staple crops potentially making its effect negligible in terms of
improving food security and self-sufficiency (Wiggins 2019).
 |
| Figure 2. A smallholder using a solar-powered irrigation system. Whilst promoted as more green alternatives and off-grid options, the systems still require significant capital investment in photovoltaic cells and pipework (Aid Forum 2018). |
It is also crucial to consider the renewability of groundwater resources to ensure their development is beneficial and sustainable in the long-term (Villhoth and Altchenko 2016). Estimations of extraction limits for the resource are important to enable sustainable agriculture, if the resource is over-exploited then catastrophe can strike. When reading a fellow students blog (Water and Food in Africa) I was intrigued by the concept of saline intrusion and how it can have serious long-term effects on agriculture. Saline intrusion is the contamination of freshwater aquifer with saltwater due to pressure differentials in the aquifer as a result of overuse and severely threatens the productivity of soil in coastal regions (Alfarrah and Walraevens 2018).
Final thoughts:
Whilst the potential for small-scale groundwater irrigation is high, the reality on the ground is extremely complex. With capital as one of the largest barriers to small-scale irrigation, micro-finance schemes and improved market access could help overcome financial constraints (WFN). While models such as that in Xie’s (et al. 2018) study and Figure 1 are useful, it is important to recognise that climate change will affect surface and groundwater resources available for farming. Thus groundwater irrigation potentials will change in accordance with resource availability and demand so continual monitoring of groundwater and crop yields is vital (Villhoth and Altchenko 2016). Before expanding groundwater irrigation, it is important that environmental flows are secured, and the use of groundwater is regulated in order to avoid overuse. With parts of sub-Saharan Africa already suffering from blue water scarcity it is important to plan expansion carefully taking into account future climate scenarios and socio-economic factors (WFN).
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