You can't see it, but that doesn't mean it's insignificant

So far, our analysis of 'hydropolitics' has been based largely on the visible: rivers, transboundary basins, and surface-level water transfer schemes. But beneath the surface, groundwater reserves embody a hugely important - yet very often overlooked - dimension, particularly across Africa. Today I will attempt to illuminate the need to consider groundwater alongside above-ground, 'blue water' sources and the merits of integrating it with existing water management paradigms by again examining our focus region of southern Africa.

Invisible importance

As posited in a 2006 USAID report, whilst integrated water resources management spells out a promising framework using surface river basins as the unit of management, it overlooks two key notions: groundwater aquifer systems often don't correspond with the surface water management unit, and groundwater systems are transboundary by nature. This is especially relevant in Africa, where 71 discrete transboundary aquifer (TBA) systems cover 42% of the continent, superimposed against 63 transboundary river basins (Altchenko and Villholth, 2013; Figure 1). 

Groundwater reserves are so important owing to its fundamental characteristics: flowing through, and stored amongst, underground sediment, it is not subject to contamination risks faced by surface sources; and with reserves 20 times that of lake and reservoir storage, it is by far the largest widespread freshwater source, relied on by millions for drinking and irrigation.

Yet, relative to surface-level water, Africa's groundwater has until more recently received little attention and hence often been utilised indiscriminately and unilaterally by parties. But in view of rising demand from climate and environmental changes, there is a need to transcend traditional perceptions of groundwater as a small-scale, extensive use source.

Figure 1: The cross-boundary nature of aquifers, as well as the sheer number of them across the continent, renders groundwater a concealed yet crucial renewable water source (Source).

Driver of neglect

Why, then, has groundwater garnered less attention? Apart from its obvious 'hidden' nature, one factor is the small volume of quantitative monitoring and information of this highly shared resource - with limited data circulated between states, a certain mindset downplaying the significance of its use is informed. Present assessments and indicators of freshwater availability also play a role: existing estimates do not factor in freshwater stored and circulated underground, while the use of mean annual river runoff in current indices like the water stress index crucially masks 'greenwater' sources like groundwater (Taylor, 2009). Use of such estimates and indices thus undermines attempts at comprehending and, by extension, managing (fresh)water availability and demands, in turn affecting allocation and regional politics.

Groundwater in southern Africa

TBAs are prone to the same - if not greater - conflict and political vulnerabilities as river basins, owing to such deficiencies in its understanding and appreciation. Whilst the largest groundwater volumes are found in North Africa's sedimentary aquifers, southern Africa is host to comparatively smaller but many more TBAs (Figure 1). Nevertheless, the region's highly transboundary groundwater has not stirred conflict.

In fact, southern Africa, under the previously introduced regional cooperation community SADC, arguably leads the continent in TBA management, with its Protocol on Shared Watercourses notably pushing for the inclusion of groundwater into the African Network of Basin's programme of activities in 2008. Beyond the mere recognition of the region's groundwater presence and importance, integration with existing river basin organisations has also been initiated, tackling the surface- and subterranean-level management unit mismatch I mentioned above. In 2007, ORASECOM created the region's first Groundwater Hydrology Committee that requires the exchange of hydrogeological data between countries and recognising the crucial co-dependencies between water resources above and below the surface (Nijsten et al., 2018).

The Tuli Karoo TBA, for example, straddles Botswana, Zimbabwe, and South Africa and serves as a vital source of water in the absence of reliable surface sources. A new groundwater monitoring system was recently established to improve conjunctive use by addressing the previous lack of accurate and up-to-date data, providing near real-time, easily accessible information on the aquifer's groundwater levels and over-exploitation warnings.

Figure 2: The monitoring system consists of a telemetry system, visualization platform, and data logger installed at wells and boreholes, such as this in Tanzania which was one of the first to be set up (Source).

Episodic intense precipitation events expected to become more common under climate change are expected to effect an overall increase in groundwater recharge (MacDonald et al., 2021). This will occur disproportionately across Africa, with arid regions in southern Africa projected to experience relatively high long-term average recharge. Combined with its relatively robust and integrated groundwater management strategies, this presents great opportunities for regional benefit by harnessing subterranean freshwater for equitable use across southern Africa.