Rainwater harvesting and management in rainfed agricultural systems in sub-Saharan Africa – A review Birhanu Biazin a,b,⇑ , Geert Sterk c , Melesse Temesgen d , Abdu Abdulkedir a , Leo Stroosnijder b a Hawassa University, Wondo Genet College of Forestry and Natural Resources, P.O. Box 128, Shashemene, Ethiopia b Wageningen University, Land Degradation and Development Group, P.O. Box 47, 6700 AA Wageningen, The Netherlands c Utrecht University, Department of Physical Geography, P.O. Box 80115, 3508 TC Utrecht, The Netherlands d Addis Ababa University, Department of Civil Engineering, P.O. Box 385, Addis Ababa, Ethiopia article info Article history: Available online 3 September 2011 Keywords: Sub-Saharan Africa Water scarcity Rainfed agriculture Rainwater harvesting Supplemental irrigation abstract Agricultural water scarcity in the predominantly rainfed agricultural system of sub-Saharan Africa (SSA) is more related to the variability of rainfall and excessive non-productive losses, than the total annual precipitation in the growing season. Less than 15% of the terrestrial precipitation takes the form of pro- ductive ‘green’ transpiration. Hence, rainwater harvesting and management (RWHM) technologies hold a significant potential for improving rainwater-use efficiency and sustaining rainfed agriculture in the region. This paper outlines the various RWHM techniques being practiced in SSA, and reviews recent research results on the performance of selected practices. So far, micro-catchment and in situ rainwater harvesting techniques are more common than rainwater irrigation techniques from macro-catchment systems. Depending on rainfall patterns and local soil characteristics, appropriate application of in situ and micro-catchment techniques could improve the soil water content of the rooting zone by up to 30%. Up to sixfold crop yields have been obtained through combinations of rainwater harvesting and fer- tiliser use, as compared to traditional practices. Supplemental irrigation of rainfed agriculture through rainwater harvesting not only reduces the risk of total crop failure due to dry spells, but also substantially improves water and crop productivity. Depending on the type of crop and the seasonal rainfall pattern, the application of RWHM techniques makes net profits more possible, compared to the meagre profit or net loss of existing systems. Implementation of rainwater harvesting may allow cereal-based smallholder farmers to shift to diversified crops, hence improving household food security, dietary status, and eco- nomic return. The much needed green revolution and adaptations to climate change in SSA should blend rainwater harvesting ideals with agronomic principles. More efforts are needed to improve the indige- nous practices, and to disseminate best practices on a wider scale. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Subsistence rainfed agriculture is the mainstay of most African economies, and contributes 10–70% to their GDP. African agricul- ture, however, has the lowest rate of productivity increase in the world. Africa was the only major region with a decline in food pro- duction per capita in the years 1980–2000 (Sachs et al., 2004). In sub-Saharan Africa (SSA), 95% of the cultivated land is under rain- fed agriculture, and an estimated 41% of the region’s population (ca. 260 million) lives in drought-prone dry lands (Svendsen et al., 2009; UNCCD, 2009). SSA has less than 2% of the world’s total irrigated land (Field, 1990). Apart from the physical water scarcity, irrigation is unaffordable in SSA, as direct investment costs alone can reach US$ 8300 ha À1 (FAO, 1992), and increase to US$ 18,000 ha À1 when indirect infrastructural costs are included (Rosegrant, 1997). Hence, for the near future, rainfed agriculture will be the dominant source of food for the region’s burgeoning population. However, water supplies in Africa are shrinking and highly var- iable. Concurrent with a huge population increase during 1970– 1994, a 180% reduction in human water supply took place in Africa while the reduction in Europe was 16% (Shiklomanov, 2000). Year- to-year variability of renewable water resources is also high in arid and semi-arid regions where actual availability is limited. It has been estimated that in dryland regions, there could be 150–200% less renewable water resources in individual years than the long- term average, whereas in wet regions this difference is in the range of just 15–25% (Shiklomanov, 1998). In addition to the scarcity and unreliability of annual rainfall, the loss of rainwater through non-productive pathways also seri- ously limits rainfed agriculture in SSA. Soil evaporation may reach 1474-7065/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2011.08.015 ⇑ Corresponding author at: Hawassa University, Wondo Genet College of Forestry and Natural Resources, P.O. Box 128, Shashemene, Ethiopia. Tel.: +251 461109900; fax: +251 461109983. E-mail address: Birhanutemesgen@yahoo.com (B. Biazin). Physics and Chemistry of the Earth 47–48 (2012) 139–151 Contents lists available at SciVerse ScienceDirect Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce