Groundwater: Potential as a water resource for irrigation

This blog post proposes groundwater as a solution to issues of water scarcity across Africa. Nevertheless, this post aims to explore the challenges that come with groundwater.

In previous blog posts, I have mentioned the Water Stress Index, which fails to take into account ground water (Damkjaer and Taylor, 2017.) Groundwater accounts for only 1% of irrigation levels in Africa however its potential has been recognised in Asia, where levels stand at 14% (Altchenko and Villholth, 2016.) Africa can benefit immensely from extracting groundwater, as 40% of sub-Saharan countries lie above rock aquifers - 0.66 million km³  (MacDonald et al,2012.) The map below highlights the variability of groundwater across Africa.

Groundwater is defined by the geology subsurface. In North Africa, aquifers are made up of sand and sandstone, which readily stores water.  Alternatively, areas consisting of crystalline rock do not store water well thus forming a weak aquifer. Groundwater has accumulated over millennia.

Benefits to Groundwater:

Groundwater extraction is particularly useful during periods of low rainfall and provide resilience to climate change (Giordono, 2005.)  Groundwater irrigation produce higher crop yields for small-scale farmers (Villholth, 2013.)  It is not dependant on seasonality and precipitation unlike rain-fed irrigation. Furthermore groundwater tends to be of higher quality.  This is due to the soil and rock providing protection for the water from contamination, unlike surface water which often require an additional cleansing process.

Groundwater projects target the poorest people relative to large-scale water management schemes. If managed sustainably,  it can provide the Sub-Saharan region with 1-2 million hectares of groundwater irrigated land, increasing the food production through a shift from smallholder subsistence farming to market-oriented farming methods. In Ghana, for example, groundwater has provided 20% higher levels of net revue per irrigated area relative to areas reliant on surface water (Dittoh et al, 2013.) A project in Zimbabwe saw an increase in income of 265% directly correlated to higher crop yields as a result of constant groundwater irrigation (Villholth, 2013.) 

Figure 1- Groundwater Storage
across Africa (MacDonald et al,2012.)

Therefore, there is no negating the significance of groundwater for agricultural use through irrigation,. Nonetheless, additional monitoring systems are necessary to efficiently and effectively extract groundwater in order to improve food security and expand groundwater-fed irrigation (Gaye
and Tindimugaya, 2019.)  The potential for groundwater is dependent on the uneven distribution of groundwater sources, see Figure 1 , depth of the water source, suitability of geology and cost of extraction mechanisms.  (Giordano, 2005.

Limitations to Groundwater:

The African continent has high levels of variability in groundwater. Whilst collectively it would seem that African has an abundance of groundwater available, the reality is that the majority of renewable groundwater supplies is located in four countries: Cameroon, The Democratic Republic of Congo, The Republic of Congo and Nigeria (Giordano, 2006.) 

Additionally, groundwater extraction can be expensive ranging from US$60 - US$360 for manual [hand] pumps or US$2,000 for motorised pumps (Villholth, 2013.) If motorised pumps require diesel to run which is more expensive and costly to the environment (Villholth and Altchenko, 2016.) Hard rock and deep aquifers, have higher levels of abstraction costs. Additional costs occur due to issues of land tenure, the wealthy can own land but those without own land are sometimes required to extract water. Nevertheless these costs occur at a fraction of other water resource schemes for example piped water. 

A final limitation to the sustainable use of groundwater is slow present day replenishment rates, as these cannot compare to those of the past. In order for the system to recharge long term management is necessary. 

Physical, socio-economic and political factors can impede the potential of groundwater within each national context. An inability to finance the necessary infrastructure lack of financing, especially across the Sub-Saharan African region, greatly limits the capacity of groundwater to aid irrigation and food production.

The Nubian Sandstone Aquifer System (NSAS):

The NSAS, shared by Chad, Egypt, Libya and Sudan, is the world's largest groundwater aquifer, covering two million square kilometres. Its vast freshwater reserves can meet growing water demands in each country. If not managed, however, the aquifer faces over-abstraction and eventual depletion as its water is ancient and non-renewable. To optimise the equitable use of the shared groundwater resource and its sustainability, the four countries have agreed on joint management of the Nubian aquifer (UN-Water, 2012.)

Overview for Next Week:

Ground water irrigation within Africa occurs most commonly through publicly funded projects (community management) or funded through the private sector. In the upcoming weeks, I will explore the possible extractions of groundwater, looking more closely at where the responsibility lies in the provision and distribution of water resources: is it the government, the community, the private sector or international funds?