Concluding thoughts and looking to the future

Groundwater holds potential for supplying Africa’s agricultural water needs. It is more climate resilient than surface waters – this should not be underestimated – and is more plentiful (estimated at more than 100 times that of annual renewable freshwater resources) (MacDonald et al. 2012). However, it has a number of drawbacks, namely its uneven distribution, the uncertainty of its quality and difficulty to manage. It will not be suitable, based on current understanding and technology, to look to it as a widespread supply of water for the majority of Africa’s agricultural demands. However, where it can be used appropriately, it should be. I hope that the future may start to deal with the drawbacks I have mentioned, such as innovations in cheaper and more efficient transportation of water, and so I am not writing off groundwater just yet.

Over-abstraction

Despite there being large amounts of groundwater (approximately 0.66 million km³ across Africa (MacDonald et al. 2012)), we still need to be cautious about how much we can abstract sustainably, because over-abstraction of groundwater supplies can have detrimental social, economic and environmental impacts (Pavelic et al. 2013). Not only can over abstraction lead to depletion of groundwater reserves, it can also have other consequences such as land subsidence, saline intrusion and increasing costs of pumping, to name a few (Ogunba 2012, European Environment Agency 2016). Consequently, management is very important.

Agricultural irrigation is a major cause of groundwater over-abstraction (European Environment Agency 2016) and managing this is very difficult with the current trends in African farming leaning towards small-holder farming. Due to increasing access to low cost pumps and climatic variability, “groundwater irrigation for small holder farmers in SSA is growing in extent and importance” (Villholth 2013: 369). A higher number of individual users makes it more difficult to impose and enforce groundwater restrictions and/or monitoring to ensure sustainable abstraction (Knuppe 2011). Small-scale, rural farmers are also more likely to have conflict with management regulation than larger irrigation companies and projects, often holding traditional attitudes and expertise (Knuppe 2011). Couple this with a rather patchy and inadequate understanding of aquifer levels and behaviour, and it makes for rather difficult management.

Groundwater for Poverty

"Eighty-five percent of Africa’s poor live in rural areas and mostly depend on agriculture for their livelihoods" (You et al. 2010: v). 

With such a high proportion of Africa's population depending upon agriculture for their income, it seems sensible that they should be provided with the opportunity to exploit and excel in this market. With rain-fed agriculture and irrigation proving climate-dependent (see previous blog post: 'Groundwater's climate resilience'), Groundwater holds the potential to not only increase the amount of land under irrigation, but to provide a more steady and stable income for Africa's poor. 

Currently, only 6% of cultivated land in Africa is irrigated, meaning the majority depend on rain-fed agriculture (PAVE Irrigation Systems 2015). Groundwater could potentially increase the total land under irrigation in Africa by 120 times, improving livelihoods for approximately 40% of the continent's rural population (Windham-Wright 2015). And with groundwater supplies proving more stable than precipitation, farmers will find themselves less susceptible to the climatic fluctuations that plague Africa. 

A Sub-Saharan African resident keeping the rewards of a groundwater-fed irrigation system 
Source: PAVE Irrigation Systems 2015

In a region so tortured by poverty, providing a steady income for many is an opportunity not to be missed. Groundwater holds the ability to do this by providing a stable and widely available resource for agricultural production. 

As stressed earlier in this blog, effective monitoring and regulation must be implemented in order to ensure supplies are not over abstracted. 

Groundwater quality

Much of the literature on groundwater in Africa is focused on quantity rather than quality. However, we must remember that sufficient water quality is needed for it to be used effectively in agricultural irrigation, and therefore it is a worthy topic to be discussed. There is limited research on this subject, so much of the impacts of climate change on groundwater quality remain uncertain and should therefore be treated cautiously. It is not the intention of this blog post to provide a comprehensive audit of the effects of climate change on groundwater quality, merely to highlight that it is something that must be considered when assessing groundwater’s potential by discussing some of its impacts.

Water quality, affected by the chemical, physical and biological changes of water, is value specific, in that its value relates to the specific activity it is needed for (Green et al. 2011, FAO 2016). For example, for agricultural irrigation, the FAO outlines a number of issues regarding water quality that can result in decreased yields or lack of effectiveness (see my summary in Table 2).

Table 2: Water quality issues, information summarised from FAO (2016)

Issue	Anticipated Result
Salinity	If salts are present in soil or water, this can reduce the water availability to the crop, potentially affecting yields.
Water Infiltration Rate	High sodium or low calcium levels in soil or water can reduce rate of entry of irrigation water. This can result in insufficient water quantities being infiltrated to supply crops between irrigations.
Specific Ion Toxicity	Ions (such as sodium, chloride or boron) can damage crops and reduce yields if they appear in sufficient concentrations.
Miscellaneous	Too high levels of nutrients can decrease yields and/or quality. Unattractive deposits on crops can reduce market potential. “Excessive corrosion of equipment increases maintenance and repairs.”

So we can see that changes in the make-up and quality of groundwater could lead it to be unsuitable for irrigation. So how is it thought that climate change will affect it? Green at al. (2011) provide a fairly comprehensive list of the possible impacts, as summarized below:

1.     Recharge during prolonged dry and wet periods may have greater and lower concentrations of salts and total dissolved solids respectively.

2.     High intensity precipitation events may cause high levels of infiltration, potentially resulting in the mobilization of “large pore-water chloride and nitrate reservoirs” in the unsaturated zone of aquifers in semi-arid/arid regions. If these reach the water table, groundwater quality may decline (544).

3.     Sea level rise, spatial and temporal variability in precipitation and evapotranspiration and increased abstraction of groundwater may lead to increased groundwater salinization in coastal regions.

4.     Increases in recharge rates could lead to growth of contaminant transport, and thus groundwater exposure to contamination.

5.     Temperature rises may alter subsurface biogeochemical reactions, potentially altering groundwater properties and quality.

6.     Increases in flood events may cause urban contaminant levels to rise in groundwater such as oil, solvents and sewage.

7.     Sea level rise, and subsequent seawater intrusion, may decrease the depth of the freshwater lens (a layer of fresh groundwater that sits on top of the denser saltwater) in coastal aquifers such as the Niger delta (Taylor et al. 2009).

It is clear that adequate water quality is important to agricultural irrigation and that the quality of groundwater is likely to change in the face of anthropological climate change. However, studies are extremely limited, and the magnitude of such predicted changes remains unclear. In addition to this, the relationship between water quality and most climatic variables in one that is non-linear, making it even more difficult to predict (IPCC 2014a). My purpose in writing this blog post is to highlight that groundwater quality should not be assumed as a constant or as suitable for irrigation. Further research is needed, and is greatly encouraged on my part, into how groundwater quality will be affected by climate change so that we are able to ascertain whether its quality allows it to remain a suitable option for agricultural irrigation.

Groundwater’s Biggest Problem: Uneven Distribution Part 2

Groundwater's Biggest Problem: Uneven Distribution Part 1

As shown in Figure 3, SSA has approximately three times the per capita groundwater availability of China and nearly six times that of India, the world's two biggest players in groundwater-fed irrigation systems (Giordano 2006). However, only 6% of cultivated land in Africa is irrigated (PAVE Irrigation Systems 2015). One of the reasons it has not been exploited to data is because Africa’s groundwater distribution is highly variable, with the majority of groundwater storage in North Africa. An intermix of factors have caused this spatial variability including geology and climate.

Geology

Supplies are dependent upon the ability of underlying rock to store and transfer water. A large proportion groundwater is located in hard rock areas or at extremely deep distances below the ground, making abstraction difficult or costly. Giordano (2006) outlines four geological zones, of which Africa is made up of (see Figure 5 for their distribution across the region), that alter the ability of the ground to store and transfer water. A summary of these zones can be found in Table 1.  

Table 1: Four geological zones across SSA, information summarized from Giordano (2006)

Hydrogeologic Zone	% of Region	Potential as a Groundwater Reserve
Crystalline Basement Rock	40	Poor supply source for groundwater due to its low transmissivity.
Consolidated Sedimentary Rock	32	Can hold large amounts of water so high potential.
Unconsolidated Sediments	22	Groundwater is often held in hold in unconstrained conditions within sands and gravels, and often found in river beds, so easily accessible. However, “many African river systems are typified by fine and very fine sediments, rather than coarse sand and gravel, reducing extraction possibilities” (312).
Volcanic Rock	6	Can produce high groundwater yields and supply springs.

However, hard rock aquifers should not be totally written off. Even those with low yield potential may be suitable for small-scale irrigation. For a community water supply fitted with a hand pump, only a sustained supply of >0.1 l s-1 is needed, in comparison to >51 l s-1 for boreholes for commercial irrigation schemes (MacDonald et al. 2012). Supplies or recharge rates may mean that these larger yields may be unreachable, but could hold potential for smaller scale, less intensive activities.

Climate

  

Groundwater also depends on recharge potential, in order to make it a sustainable resource. Unfortunately, due to past and current climatic conditions, groundwater distribution is highly correlated with rainfall patterns, meaning it tends to be highest in areas of high rainfall and lowest in areas of low rainfall (Calow and MacDonald 2009). This depletes the human value of groundwater. 

Depth to Groundwater

The depth of the groundwater below the surface is again, unsurprisingly, highly variable. Depth affects both the practical accessibility of the resource, and whether it is economically viable (MacDonald et al. 2012). Levels deeper than 50m are not easily accessible by a hand pump and for those >100m, the cost of extraction increases dramatically because more advanced drilling equipment is required (MacDonald et al. 2012).