Better control of water is often cited as one of the most important elements for improving agricultural performance and the livelihood of the rural poor in sub-Saharan Africa (SSA). A key reason for this contention is the high variability in the region's natural water supplies. In fact, the spatial and temporal unevenness of the area's water resources (rainfall, river flows and groundwater) is perhaps the greatest of any major region of the world and is of concern in both low and high rainfall areas. While the construction of surface water storage and irrigation could help to even out water distribution - making it easier to take advantage of the Green Revolution and other technologies that revolutionized agricultural landscapes and food supplies in much of Asia - physical, economic and political factors have often hindered their development in SSA. In such circumstances, groundwater would seem to have great potential for a variety of reasons.

Groundwater has been described as a perennial source of water (Calow et a/., 1997), a much needed buffer during times of drought (Carter, 1988, in Carter, 2003), and a resource that can be developed for localized use (Butterworth et a/., 2001). Carter (2003) even describes groundwater as the ultimate resource for use at local scale, both because it lends itself to incremental development at relatively low cost and because it is more resilient to interannual variability than surface water is. With reference to groundwater, availability where it is needed reduces the need for large-scale infrastructure investments and low variability obviously counters fluctuations in surface supplies - two key issues in the region. Despite these positive and potential attributes, especially in the SSA context, groundwater plays only a relatively limited role.

The reason for the modest groundwater use across all sectors is partly because the hydrogeologic formations underlying most of SSA are not of the type necessary to supply large-scale water resources development. However, the lack of ┬ęCAB International 2007. The Agricultural Groundwater Revolution:

Opportunities and Threats to Development (M. Giordano and K.G. Villholth) 79

similarity to traditional groundwater regions can lead to an underappreciation of the use that does exist in SSA. At the extreme, an estimated 80% of human (mostly rural) and livestock populations in Botswana depend entirely on groundwater (Chenje and Johnson, 1996, in Nicol, 2002), with groundwater contributing up to 65% of all water consumed (Noble et a/., 2002). Groundwater is also critical for livestock production in large parts of the Sahel and East Africa. Similarly it plays a critical role in supplying water for small-scale but highly valuable irrigation as well as in stabilizing water supplies in times of drought. Numerous reports highlight the major role groundwater plays in rural domestic supply (BGS, 2000; Carter, 2003). The data on groundwater use are often found distributed among many agencies - donor offices, central government departments and local governments. Other abstraction points are unknown as they are privately installed. It is therefore difficult to estimate actual numbers involved, but the majority of poor rural households depend on groundwater for domestic supply, livestock, crop production and other purposes. Thus an appreciation of the impact of groundwater use in SSA agriculture goes beyond simple calculations of irrigated area to include livestock maintenance, drought mitigation and broader rural livelihood support.

In the past, there have been few attempts at broad-scale research on the role of groundwater in agricultural livelihood in the SSA context and even fewer attempts to quantify that role. As knowledge on this subject is relatively poor, the goal of this paper is to develop as full a picture as possible based generally on published information so as to consolidate known information, highlight critical gaps and inform further research on groundwater and its potential role in solving Africa's water and poverty problems. The paper is divided into four parts: an overview of the known groundwater resources of SSA and their relationship to human population; an overview of agricultural groundwater use and extent, highlighting groundwater's various roles and their possible contribution to rural livelihoods; the state of groundwater governance; and a set of recommendations for development of, and research on, groundwater in SSA.

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