The Opportunities and Challenges of Small-Scale Groundwater Irrigation

Today I came across a video on YouTube from the Water for Food Global Conference. A focus on small-holder farmers in Sub-Saharan Africa (SSA) was unsurprising given that, in countries like Malawi, over 90% of the national population are dependent on them for survival (Toenniessen et al. 2008). The consequences of failing to increase average agricultural yields for several decades, along with a dependence on substantial cereal imports to meet consumption (Ittersum et al. 2016), has left SSA vulnerable to the challenges of food insecurity; with projections of an increase in population by at least one billion by 2050, a solution is needed. Consequently, this post will explore the utility of developing small-holder groundwater irrigation (GWI) in SSA – have a look at my previous post where I introduced groundwater in Africa.

With less than 5% of the arable land in SSA irrigated, a shift from rain-fed farming to irrigated farming was advocated throughout the conference. Rain-fed farming results in harvests at the same time of year for most farmers who end up selling into flooded markets at low prices and, inevitably, the supply of food far exceeds demand meaning 45% of their produce is spoiled before it can be sold. Irrigated agriculture, on the other hand, enables year-round production of higher value crops and huge economic benefits due to the high prices farmers can sell at. In fact, Martin Fisher, a panellist at the conference, reports GWI produces a two-and-a-half-fold increase in yields which translates to a four-fold increase in income. This is especially important in the face of increasing climate variability which threatens consistent crop production and economic development.

The reasons for the increasing prevalence of small-holder GWI in SSA have already been elucidated. However, the recognition that large-scale schemes often fail to successfully target, and benefit, the poorest (Naugle and Sellen 2006), alongside the ‘individual modes of uptake and operation’ (Villholth 2013: 370) involved in small-holder GWI, has made it particularly attractive to farmers. 

Unfortunately, GWI isn’t without its risks and careful resource development must take place to avoid unsustainable use.

GWI and the Physical Landscape

Extensive GWI is strongly limited by its distribution (Figure 1). The underlying geology of different parts of Africa (Figure 2) also varies and this has a strong influence on groundwater storage and aquifer productivity, as outlined by MacDonald et al. (2009). Precambrian basement rocks offer little as a groundwater resource whereas consolidated sedimentary rocks are diverse, exhibiting considerable differences in permeability. Mudstone, for example, has a low permeability compared to limestone; nevertheless, an accurate assessment of underlying mudstone can still yield abundant levels of groundwater for irrigation (MacDonald et al. 2005). Largely found in eastern Africa, volcanic rocks offer huge GWI potential as they are distributed in drought vulnerable regions.

Figure 1. A map outlining the distribution in groundwater storage in Africa. (Source: BGS)

Figure 2. A map outlining the hydrogeological environments of Africa. (Source: MacDonald et al. 2009)

The sustainability of groundwater resources in areas where the geology is unfavourable is regulated by rainfall due to its control on aquifer recharge. Semi-arid areas like Tanzania receive vital recharge during extreme precipitation events, supporting the physical sustainability of GWI. However, these events are highly localised and infrequent in comparison to the recharge of the aquifers of the inner tropics. Here, despite being characterised by low-storage aquifers due to the mixture of consolidated and unconsolidated geology, monsoonal rainfall triggers regular replenishment (Taylor et al. 2012).

GWI and the Environment and Society

Further pressure is placed on GWI because of climate change. Having just spoke of the contribution of intense rainfall to the sustainability of GWI, it goes without saying that its concomitant floods pose a real challenge for shallow groundwater resources. Shallow groundwater in both rural and urban areas is at risk of contamination due to high population densities and poor sanitation. Furthermore, elevated water tables during the rainy season can wash pathogens into groundwater (Pritchard et al. 2008) and a failure to properly construct water supplies to circumvent polluted groundwater can severely diminish the applicability of GWI. The danger of polluted groundwater is also pervasive in arid and semi-arid areas where high levels of evapotranspiration enable salt leaching (Villholth 2013); countries where rainfall is unpredictable and groundwater resources are negligible face the biggest challenges e.g. Kenya and Tanzania.

Additional constraints of GWI correspond to economic obstructions whereby the poorest farmers either struggle to produce capital for the initial adoption of GWI techniques or cannot efficiently maintain equipment. Given that deeper groundwater offers a more dependable, safe and perennial supply of water, but prices for investing and maintaining these systems are higher, marginalised groups, like women, are unlikely to wholly benefit from GWI. Instead, this may serve to perpetuate social and economic inequalities across communities in SSA.

In concluding this post, I hope to have offered an insight into the importance of groundwater for small-holder farmers and the potential GWI holds for improving food production and, hopefully, security. It is clear that the challenges associated with GWI must be addressed to prevent the degradation of groundwater resources and this should be explored through efforts to improve the capacity for communities and institutions to manage groundwater resources. Understanding that GWI is supplementary to rainfall, and not completely independent, is also vital if we are to develop a means of improving food production across SSA.    

What are your thoughts? How significant do you think the limitations of GWI are?