Water-balance approach for assessing potential for smallholder groundwater irrigation in Sub-Saharan Africa

Water-balance approach for assessing potential for smallholder groundwater irrigation in Sub-Saharan Africa P Pavelic1*, V Smakhtin2, G Favreau3 and KG Villholth4 International Water Management Institute, Vientiane, Lao PDR International Water Management Institute, Colombo, Sri Lanka 3 IRD, HydroSciences Montpellier, France 4 International Water Management Institute, Pretoria, South Africa 1 2 Abstract Strategies for increasing the development and use of groundwater for agriculture over much of Sub-Saharan Africa (SSA) are urgently needed. Expansion of small-scale groundwater irrigation offers an attractive option to smallholder farmers to overcome unreliable wet-season rainfall and enhance dry-season production. This paper presents a simple, generic groundwater-balance-based methodology that uses a set of type-curves to assist with decision making on the scope for developing sustainable groundwater irrigation supplies, and to help understand how cropping choices influence the potential areal extent of irrigation. Guidance to avoid over-exploitation of the resource is also provided. The methodology is applied to 2 sites in West Africa with contrasting climatic and subsurface conditions. At both sites the analysis reveals that there is significant potential for further groundwater development for irrigation whilst allowing provisions for other sectoral uses, including basic human needs and the environment. Keywords: groundwater irrigation, water balance, over-exploitation, Sub-Saharan Africa Introduction Enhanced groundwater irrigation for smallholder agriculture in Sub-Saharan Africa (SSA) is widely recognised as being an important aspirational goal that would dramatically improve food security and livelihoods by protecting against poor and highly variable wet-season rainfall and by enabling productive use of land during the dry season (Kay, 2001; Allaire, 2009). However, groundwater-sourced agricultural development across SSA has been severely lagging behind most other regions of the world (Shah et al., 2007). Less than 2% of rural households are served by groundwater for irrigation purposes in SSA, whereas, in contrast, the figures for China and India may be in the order of 30% and 50%, respectively (Giordano, 2005). According to national-level figures from a cross-section of 16 SSA countries, groundwater is being used to irrigate less than 1% of the arable land (Table 1). At the same time, positive developments are emerging, with groundwater being increasingly recognised as a largely untapped resource for agricultural development in SSA, albeit with numerous technical and non-technical issues which severely constrain development (Giordano, 2006; Masiyandima and Giordano, 2007). There is emerging evidence that farmers are increasingly resorting to groundwater for irrigating high-value crops across Ghana where there is much optimism amongst decision-makers and investors that groundwater can play an important role in enhancing productivity and alleviate poverty (Namara et al., 2011). Other successful examples of agricultural groundwater development, often using rudimentary abstraction technologies This paper was originally presented at the International Conference on Groundwater: Our Source of Security in an Uncertain Future, Pretoria, 19-21 September 2011. * To whom all correspondence should be addressed.  +856-21-771438; fax: +856-21-770076; e-mail: include the fadama cropping systems along the inland valley areas of Nigeria (Tarhule and Woo, 1997). In countries such as Ethiopia and Zimbabwe, smallholder farmers with higher, yearround access to irrigation water through the use of groundwater are better able to produce higher-valued, marketable vegetables than those without (Hagos et al., 2009). These examples offer hope for the expansion of areas under cultivation and higher cropping intensities if technical, technological, economic and policy-related barriers can be overcome. One of the issues that must be addressed when proposing new groundwater irrigation development for smallholder farmers is the threat of over-abstraction posed to existing groundwater users, along with the ecosystems supported by groundwater. In countries such as South Africa, where groundwater irrigation development is the most advanced within the SSA region (Table 1), as well as in some other countries in the lower rainfall zones, commercial-scale developments have in some cases already led to continuously falling groundwater levels (Wada et al., 2010). Across much of the region, very little is known about the physical extent, accessibility and development potential of groundwater, but interest and knowledge are emerging (Namara et al., 2011). Data availability remains scarce, and that which is being gathered is often being collected unsystematically and disconnected from information systems (Adelana and MacDonald, 2008). Not only is the quantum of information and the level of understanding often very poor, it is also highly heterogeneous across the region, which makes it difficult to perform broad-scale assessments. As a result, uncertainties and misconceptions emerge about the development potential. In areas where the development of the groundwater resources is low, the extent of smallholder irrigation that could be introduced is usually unknown. Given the above-mentioned challenges, simple methods that follow ‘start small and learnas-you-go’ principles are needed in order to gauge the levels of irrigation development that can be sustained, and to determine http://dx.doi.org/10.4314/wsa.v38i3.5 Available on website http://www.wrc.org.za ISSN 0378-4738 (Print) = Water SA Vol. 38 No. 3 International Conference on Groundwater Special Edition 2012 ISSN 1816-7950 (On-line) = Water SA Vol. 38 No. 3 International Conference on Groundwater Special Edition 2012 399 strategies to ensure that the appropriate type and level of development will take place. In this paper a simple methodological framework is presented that aids in the estimation of upper limits of groundwater development for irrigation in terms of volumes of abstraction and irrigated area. The methodology is then applied to 2 case-study areas in West Africa to demonstrate its applicability and utility. Table 1 Estimates of groundwater use for irrigation in selected Sub-Saharan African countries. Sources: Siebert et al. (2010) and FAOSTAT (2011) Country Botswana Burkina Faso Ethiopia Ghana Kenya Malawi Mali Mozambique Niger Nigeria South Africa Sudan (N&S) Tanzania Uganda Zambia Zimbabwe Groundwater irrigated area (ha) Percentage of arable land 286 3 000 2 611 12 000 970 30 750 217 1 221 64 000 127 330 29 732 17 465 59 6 646 14 277 0.11 0.05 0.39 0.27 0.02 0.00 0.02 0.00 0.01 0.17 0.88 0.14 0.18 0.00 0.28 0.38 Methodological development Principles and approach In groundwater systems that are actively replenished, it is generally accepted that the sustainable yield of an aquifer determines the allowable extent of groundwate (...truncated)