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

P Pavelic,G Favreau,Kg Villholth,V Smakhtin

doi:10.4314/wsa.v38i3.5

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.

Highlights

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)
An alternative approach, proposed by Seward et al (2006) uses the concept of ‘capturable’ storage rather than recharge to define sustainability criteria. This approach is probably more accurate than that proposed here, since it describes the physical processes more accurately, but application is limited to cases where there is sufficient data. It is worthwhile noting the work of Dillon et al (2009) who used a simple mass-balance approach to assess the sustainability of groundwater irrigation, but with a focus on the role and significance of managed aquifer recharge as supply-anddemand-based counterbalances to the problem of groundwater overdraft
When the measured value of crop water demand of 770 mm∙yr-1 for tomato crops and the total area under groundwater irrigation is used, the Qi accounts for 18% of relationships between water availability (Rt), a value much higher than that derived by Martin (2006)

Summary

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). The ambient component represents the long-term, relatively stable storage whilst the active storage is subject to annual groundwater-level fluctuations due to recharge and discharge fluxes.

Results

Conclusion