West, East and Southern African Groundwater

I discussed fifteen countries in Sub-Saharan Africa and showed the results of Pavelic et al's book on groundwater. Grouping the region into West, East and South can provide useful insight as they are often either geographically or socially similar.

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Burkina Faso, Ghana, Mali, Niger and Nigeria are all West African countries largely dominated by Precambrian basement. In such a formation, groundwater tends to collect due to secondary porosity (as opposed to the porosity of the rock itself) due to chemical weathering, fracturing or jointing. Within these spaces is groundwater suitable for use. Aquifers in the crystalline basement rocks generally have the lowest yields ( > 1L/s). Higher yields from boreholes tend to be from sedimentary aquifers (> 20L/s). 

In this region, most groundwater is used for drinking water. Regarding how the water is used, 'Drinking water supplies sourced from groundwater for rural/small towns serve 33 percent of Ghana, 92 percent of Niger, 70 percent of Nigeria and 55 percent of Mali. Burkina Faso uses groundwater as the principal source of supply in small towns and rural areas.' This is especially important for populations living in the Sahelian zone who experience infrequent and variable rains.

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Contrastingly, the basement of Malawi, Mozambique, South Africa, Zambia and Zimbabwe in Southern Africa is predominantly crystalline. Groundwater tends to collect in fractured bedrock and weathered regolith. The groundwater aquifers in Southern Africa tend to be relatively poor due to low capacity and water quality. There are some boreholes with higher yields (>80L/s), such as the Limpopo basin and Zambian/Zimbabwean limestone aquifers, but the majority is poor.

Again, most groundwater is used for drinking, although some is used for remote mining activities. Drinking water supplies sourced from groundwater for rural/small towns serve 51 percent of Zambia, 70 percent of Zimbabwe, 65 percent of Malawi, 60 percent of Mozambique and 60 percent of South Africa'. Groundwater irrigation demand has been increasing, such as in the area around Lusaka, Zambia. The negative impacts around Lusaka have been well documented, and I might look into it in a later post.

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Similar to South Africa, the countries studied in East Africa have low groundwater reserves. Kenya, Somalia, Tanzania, Uganda and Ethiopia sit atop a Precambrian basement complex. On top of this are new, younger formations than hold groundwater reserves. The rifts and fractures in volcanic highlands and alluvial valleys have very productive aquifers, although shallow. The highest yields in East Africa are about 6L/s, relatively low compared to the other two regions.

Of the regions, groundwater irrigation use in East Africa is the lowest. Groundwater irrigation is a key source of water, especially in some arid areas where it is the only source. 'Drinking water supplies sourced from groundwater for rural/small towns serve 85 percent of Ethiopia, 50 percent of Kenya, 70 percent of Somalia, 56 percent of Tanzania and 70 percent of Uganda.' Large swathes of East Africa are in the Sahel region that only receive rainfall once a year due to the ITCZ circulation (see here for explanation). As such, during the dry season, and especially if the rains fail, groundwater is of utmost importance.

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All three regions discussed use groundwater significantly and without it the land probably could not sustain the populations it does. As promised, next I'm going to look at Ghana. 

Groundwater Case Study Assessment

As discussed, groundwater varies hugely throughout Africa. As does population, socioeconomic position and demand for water. Therefore, each case for groundwater needs to be judged individually, a mammoth task. The inherent variability means that traditional proxies are actually quite ineffective as different variables carry different weightings for different regions.

Pavelic et al. have published a book assessing 'Groundwater availability and use in Sub-Saharan Africa: A review of 15 countries'. In the book they take fifteen country scale case studies: Burkina Faso, Ethiopia, Ghana, Kenya, Malawi, Mali, Mozambique, Niger, Nigeria, Somalia, South Africa, Tanzania, Uganda, Zambia and Zimbabwe. If anyone has a particular interested in any of the case studies I'd definitely go over them, on average they're only about 20 pages and all written by country experts.

In later posts I'm going to analyse groundwater in Ghana, a country I have a specific interest in  I've spent time in Ghana doing charity work and observed groundwater pumps and rainwater collection schemes.

The conclusions of Pavelic et al's book are as follows, note how they do fall into the trap of trying to assign a score or a proxy measure to such water resources just analyse each on their own merit:

Through not ranking these issues, the book highlights the problems each country has with harnessing groundwater without comparing them.

Groundwater Availability

On my last post I received a question about the availability of groundwater supplies, and then whether they were expensive.

The volume of groundwater stored in Africa is estimated to be 0.66million km3, more than 100 times annual renewable freshwater resources, and 20 times the freshwater stored in lakes. This is why groundwater is seen as a potential buffer to climate variability and change.

Let me set the scene of groundwater in Africa. The inconsistency of groundwater distribution is huge; regarding the variability in groundwater storage, recharge, depth and aquifer productiveness.

To illustrate this, MacDonald et al. released a brilliant paper in which they map groundwater resources in Africa. The reason I'm fond of papers such as this is the production of maps means their research can easily be consumed by a wider audience outside of academia, something I myself am hoping to achieve with my blog. If the aim of geographical research is to inform policy change, then the spread of knowledge to inform opinion outside the sphere of academia can have a major impact, and this paper achieves that. Below are three of the maps from MacDonald et al.'s paper.
 

Groundwater storage for Africa in mm, with modern annual groundwater  recharge added for comparison from Doll and Fiedler  groundwater modelling.

Aquifer productivity for boreholes appropriately drilled and sited using appropriate techniques and expertise. The inset shows  the depth to groundwater, from Bonsor and MacDonald.

Panel (a) is the proportion of land area within each geological category that is attributed to a particular class of aquifer productivity, and panel (b) shows the distribution of said categories throughout Africa.

These maps show the need for individual case study assessments before an African country should decide whether to use groundwater. I will take this further my studying some specific groundwater cases in my next post.

Groundwater as a solution?

Rainfall patterns in Africa are set to increase in variability with climate change. Furthermore, increased temperatures mean air holds more water before saturating and therefore rainfall events are going to be less frequent and heavier. With these changes, Africa needs to adapt to climate change.

Stephen Ngigi (2009) proposes that groundwater could aid smallholders in adapting to such increased climate variability. Smallholders are the poorest farmers, generally owning less than two hectares of land. Not only can smallholder irrigation help climate change adaption, but it can promote poverty alleviation, labour productivity, general economic development and rural employment (Villhoth, 2013). Villhoth excellently summarises the current knowledge regarding groundwater irrigation for smallholders, which makes up the majority of sub-Saharan Africa's employment and agricultural produce. However, as a summary of so many groundwater thematic-areas in only 32 pages it is limited in detail.

So why can groundwater help? Farmers tend to favour groundwater because of its consistently. Due to the nature of the ITCZ's annual variability, rivers in Africa tend to be much less consistent than elsewhere on the planet (see three selected rivers below).

Taylor (2006), Chapter 8

Such variability makes groundwater attractive to smallholders due to autonomy over its control. Therefore, risk is lower, outputs are more stable and productivity increases (Villhoth, 2013). In Northern Ghana Dittoh et al. (2013) found that manual groundwater irrigation produced an average gross revenue per hectare of $884.87, compared to $618.22 for manual surface water irrigation.

Groundwater produces a constant supply of water to smallholder farmers in a region with unmatched climate variability, problem solved? Not quite. These groundwater resources are not necessarily renewable or sustainable. These fossil groundwater systems have been created by historic rainfall and regeneration rates from contemporary water generation are tiny compared to the potential extraction... perhaps sounds similar to another resource we use?

Already over 80% of domestic rural water supplies in sub-Saharan Africa are from groundwater, and South East Asia has proven what groundwater abstraction can do to agricultural productivity. The added control over supply is the clear benefit and explains the drive for groundwater pumps, but are they a sustainable solution? I'll be looking into the sustainable feasibility of groundwater pumps in Africa in a later post.

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Combined Climate Change Risk

In my previous three posts I have summaries the three main risks climate change poses to Africa: changing rainfall patterns, adaptability and temperature increase.

It is this the combined climate risk of this three-faced threat that puts African life and development in such danger, perhaps if only one of these problems was occurring it could be dealt with. Although I've posted it previously, this IPCC summary clearly illustrates what Africa is up against.

To aid Africa the developed world must try and keep climate change to a minimum through lowering emissions and provide help to increase Africa's adaptability. Having established the problem, I will now post about how Africa might look to deal with the issue.

Climate Change Risks: Temperature Change

Global temperatures have already risen by 0.85 degrees, and are predicted to rise further. Below is a projection of four carbon dioxide emission scenarios and the temperature increases that will result: low, medium, medium-high and high emissions.

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The low emission scenario is extremely unlikely requiring co-operated global mitigation on a huge scale. Whichever of the other three emissions scenario occurs it will have profound impacts on much of Africa. This is because a temperature increase will increase evapotranspiration, obvious right? But in water scare regions, like large sections of Africa, the impact of this can be devastating.

For example, if rainfall is 1200mm and evapotranspiration equivalent to 1000mm in a given catchment, flow will be 200mm. A 10% rise in evapotranspiration to 1100mm will then reduce flow 50% to 100mm. This is a similar relationship to how I describe when considering changing rainfall patterns.

The above scenario that best represents future climatic conditions is up to humans and how we managed our emissions. The smaller the temperature change the easier job Africa will have, but the increase in evapotranspiration will have major impacts on future water supply.