Investigating Africa's Future Water Supply

My last post highlighted how the African agricultural sectors huge reliance on highly variable rainwater resources constrains agricultural production in turn perpetuating food insecurity and poverty. As a consequence of climate change, rainfall will become increasingly unpredictable and variable. It is therefore crucial that Africa explores and adopts alternative means of providing adequate water supplies. Especially because, as is widely noted, Africa has sufficient water supplies and the continents water crisis isn’t one of volume but of spatial and temporal distribution (The Africa Water Vision for 2025). I will now briefly explore some of Africa's potential options and what role they may play in Africa’s ambitions (and need) to achieve water and food security.

Dams and Reservoirs

One option for combatting the increasingly varied and unreliable atmospheric provision of water is to store water when it is available, for using when it is not available i.e. in large reservoirs and smaller rain-water harvesting systems. As McCartney and Smakhtin highlight, water storage increases water security, agricultural productivity and adaptive capacity to climate change (McCartney and Smakhtin 2010). Formed by the creation of a dam, reservoirs have the capacity to store large amounts of water and therefore facilitate provision of a more reliable and consistent water supply.

Cahora Bassa Dam in Mozambique is one of the three major dams on the Zambezi river system
Source: trekearth.com

However, with all of the great positive aspects of dams and reservoirs there are some equally negative aspects of these engineering projects. Firstly, the construction (and maintenance) of dams is hugely expensive and environmentally disrupting and damaging. They also cause (often irreversible) upheaval to people living both near the site and far downstream from it. As well, because so many of Africa's river basins are transboundary, construction of dams has international implications. Most reservoirs have a large surface area and relatively shallow depths which means a significant proportion of the water (sometimes 90%) is lost to evaporation. The capacity of reservoirs to hold a large volume of water is both an advantage and disadvantage. With the water held in one area reservoirs are a centralised resource. As a result, in addition to the implications of the dam/reservoir construction, a large amount of infrastructure is necessary to transport the water from where it is stored to where it is needed. This adds further disruption, destruction, cost and maintenance.

As well, because the construction of dams and reservoirs is so expensive they are often funded / constructed by aid from developed countries. McCartney and Smakhtin highlight that both the European Union and China are investing significantly in water storage infrastructure throughout Africa. Foreign involvement in the affairs of African countries further implicates these engineering projects in controversy and political tensions.

Rain-water Harvesting Systems

Rain-water harvesting systems (RWHS’s) or small water storage systems are significantly smaller than reservoirs. Crucially, instead of being centralised stores of water they are at (or at least close to) the site of the water need. Therefore, RWHS’s require far less infrastructure compared to dams and reservoirs and thus they are far less disruptive and a more sustainable water storage option. Aside from increasing water security, agricultural productivity and adaptive capacity RWHS’s can also significantly improve the local people’s livelihoods and health.

Diagram of a Rainwater Harvesting System
Source: http://armfielddesign.com/

Indeed, stored water in reservoirs and rain-water harvesting systems provides a means of adapting to increasing rainfall variability and crop failure can be prevented and yields sustained (and potentially increases) if the water is used for irrigation. However, investing in water storage won’t immediately bring these benefits; context is also important.

At present, less than 5% of the cultivated area in SSA is equipped for irrigation. Therefore, achieving food security in Africa will not be as simple as just increasing water storage capacity; investment in irrigation infrastructure will also be crucial. This sentiment is reflected in the fact that one of the goals of Africa Water Vision 2025 is to at least double the area of Africa that is under irrigation by 2025.

Groundwater Extraction

Groundwater is already heavily relied upon as a source of drinking water in Africa. Increasing its extraction is another option for tackling Africa’s water/food insecurity and responding to climate change and population growth. In 2012, MacDonald et al. presented maps that showed African freshwater stored as groundwater is well-distributed across the continent and there is an estimated 0.66 million km3 of water; more than 100 times the annual renewable freshwater resources. The maps also show that many of the countries designated as ‘water scarce’ have substantial groundwater reserves.

Groundwater storage for Africa based on the effective porosity and saturated aquifer thickness. Groundwater storage is expressed as water depth in millimetres with modern annual recharge for comparison.
Source: MacDonald et. al., 2012

One of the advantages of aquifers compared to reservoir stored water is that groundwater is not nearly as affected by evaporation. As well, because Africa’s groundwater resources are well-distributed, water can be found close to the site of need and therefore extensive water transportation infrastructure is not necessary (McDonald et. al 2012). Additionally, McDonald et. al highlight that groundwater often doesn’t require treatment or processing.

Despite the great abundance and presence of groundwater, the extent to which groundwater can facilitate water/food security and adaptation to climate change will be determined by the accessibility of said water. Abstraction of most groundwater requires drilling a borehole. However, the characteristics of the rock above the water (e.g. its permeability) determines the yield and abstraction rate of the borehole. Therefore, ability to access the water is equally as important as its abundance (McCartney and Smakhtin, 2010. McDonald et. al, 2012).

In their paper, McDonald et. al conclude that: 

·      The potential for borehole yields exceeding 5 l s−1 (required for commercial irrigation) is not widespread and higher yielding boreholes may only be successful in some areas.

·      The potential for boreholes yields of 0.5–5 l s−1, which could be suitable for small scale household and community irrigation, or multiple use water supply systems, is much higher.

Aquifer productivity for Africa showing the likely interquartile range for boreholes drilled and sited using appropriate techniques and expertise. The inset shows an approximate depth to groundwater. (Bonsor and MacDonald 2012 in MacDonald et. al 2012).  
  

Therefore, it seems that despite its huge potential, exploitation of groundwater resources will not
necessarily be simple or a universal panacea. However, this isn’t to say that groundwater extraction
should be disregarded as an option because there are certainly cases where it can make a considerable
contribution to combatting African water and food security and poverty levels.

Additionally, because the boundaries of groundwater stores are not synonymous with national boundaries, over 80 aquifers and aquifer systems in Africa are shared internationally (Villholth and Altchenko, 2014). This creates legal issues surrounding ownership and sharing of groundwater and further questions to what extent groundwater abstraction will form part of Africa’s future.  

All of the water storage options discussed have strengths and weaknesses which depend, in part, upon their inherent characteristics but they also affected by site-specific conditions and the way in which each option is installed and managed. Indeed, none of the storage options will be a panacea. However, in the correct geographic, cultural and political location they all have important contributions to make toward achieving Africa’s ambitions (and need) to achieve water/food security and reduce poverty. I guess it's a case of watch this space...

Africa Water Atlas. (2010). 1st ed. Nairobi, Kenya: United Nations Environment Program.

MacDonald, A., Bonsor, H., Dochartaigh, B. and Taylor, R. (2012). Quantitative maps of groundwater resources in Africa. Environmental Research Letters, 7(2), p.024009.

McCartney, M. and Smakhtin, V. (2010). Water Storage in an Era of Climate Change: Addressing the Challenge of Increasing Rainfall Variability. Available at: http://www.iwmi.cgiar.org/Publications/Blue_Papers/PDF/Blue_Paper_2010-final.pdf?galog=no

The Africa Water Vision for 2025. (2009). 1st ed. Addis Ababa: Economic Commission for Africa.

Villholth, K. and Altchenko, Y. (2014). Transboundary Aquifer Mapping and Management in Africa. Iwmi.cgiar.org. Available at: http://www.iwmi.cgiar.org/Publications/Other/PDF/transboundary_aquifer_mapping_and_management_in_africa.pdf?galog=no

Re-evaluating Africa's Reliance on Rainwater

I hope that my last post provided an insight in to the complex nature of Africa’s food insecurity.  The post highlighted that achieving food security in Africa will require changes across many sectors and coordination between these sectors. To achieve food security (as well as increased agricultural productivity, economic development and sustaining an increasing population) a foundation of the ability to access and utilise reliable water sources will also be essential.

The physical landscape plays a very significant role in determining the climate of an area, and the African land mass is no exception. A low-pressure area called the Inter-Tropical Convergence Zone (ITCZ) lies across the African continent, just north of the geographical equator. The ITCZ is an area of convergence where the moist trade winds meet. Upon meeting, their warm air rises, cools and then sheds its moisture in the form of precipitation. The air, now containing little water, moves poleward and descends providing little precipitation.

The ITCZ creates a latitudinal symmetry of precipitation across Africa; increasing distance from the equator correlates with decreased length, amount and reliability of rainfall. Complicating matters, the rainfall on the continent is highly variable at inter-annual, decadal and longer time scales. This variability has also been exacerbated by climate change and global warming. Therefore, the physical environment plays a large role in determining the geographical distribution of water resources and therefore water scarcity across Africa. Naturally, humans cannot alter the seasonality, variability and locality of precipitation distribution (although, climate change is negatively influencing this), but, what they can influence is how available water is used and managed.  

Annual Average Total Precipitation 1979-2011 (Source: http://www.esrl.noaa.gov/psd/)

The total amount of water available for usage is essentially not going to change and besides Africa has sufficient supplies of water for achieving food security (Africa Water Atlas, 2010). Therefore, the problem is not of quantity but accessibility and distribution (both temporally and spatially). Nevertheless, if food security in Africa is to be achieved, an increase in water supply to the agricultural sector will be crucial. Therefore, efficiency of water use must increase and sustainable management of available water resources must also become paramount.

However, water management is expected to become increasingly challenging because the predicted effects of anthropogenic global warming are yet to be fully realised. Allan and Soden predict that Africa as a continent will warm more than the global mean. Consequently, variability in rainfall and river discharge will increase disproportionately, with weather becoming more extreme and unpredictable (Allan and Soden, 2008). This is also compounded by a predicted increase in the inter-annual variability of rainfall. Therefore, provision of water supplies from precipitation are already and will increasingly become unpredictable and unreliable.

At present, 95% of Sub-Saharan Africa’s agricultural activity relies solely upon rainfall (Africa Water Atlas, 2010). Therefore, the present (and predicted) increase in variability of rainfall, river discharge and water supplies presents a huge barrier to achieving the expected multitude of benefits of investing in the agricultural sector i.e. food security, economic development, reduced poverty rate and reduced urbanization. Essentially, if investment is going to have its intended effects, rainfall cannot be relied upon to provide a reliable water supply to the agricultural sector.

However, this is no reason to lose faith in the possibilities for African agriculture. In fact, there exists sufficient water on the continent of Africa to achieve food security, (Africa Water Atlas, 2010), the challenge is how to exploit such resources. Therefore, a transition away from agriculture’s reliance on rainwater and toward utilising alternative means of acquiring the necessary water is required.

Some possible alternatives to rainwater include:

1)    Construction of dams to create reservoirs for storing water

2)    Rainwater harvesting

3)    Abstraction of Groundwater

4)    Adapting farming practices to work with the new environmental conditions

Naturally, these potential alternatives have advantages, limitations and present new challenges. As well, each option will not be universally appropriate, necessary or indeed possible. Some are also small-scale options whereas others are very much large-scale solutions. There is a clear need to be locally and contextually specific when making decisions on how to manage water. Whilst precipitation and climate become increasingly variable and there persists a need to ensure water and food security, all of the above alternatives will probably form part of Africa’s future. My next post will examine some of the potential alternatives outlined above and investigate how they may form a part of Africa’s ambition to achieve water and food security.

Africa Water Atlas. (2010). 1st ed. Nairobi, Kenya: United Nations Environment Program.

Allan, R. and Soden, B. (2008). Atmospheric Warming and the Amplification of Precipitation Extremes. Science, 321(5895), pp.1481-1484.

BBC.co.uk. (2016). BBC Bitesize - Higher Geography - The cause and impact of the Intertropical Convergence Zone - Revision 1. 

Esrl.noaa.gov. (2016). ECHAM 5 AGCM Simulations Focused on Africa (Climatology and Trends).