Using Rainwater for Off-Season Small-Scale Irrigation in Arid and Semi-arid Areas of Sub-Saharan Africa: Key Working Principles and Best Practices

The performance and cost-efficiency of off-season small-scale irrigation in arid and semi-arid areas of sub-Saharan Africa can be optimised by means of off-season rainwater harvesting irrigation management (RWHI), which is a subset of rainwater harvesting technologies and practices that allows concentrating and storing rainwater to be used for off-season small-scale irrigation of high-value crops in arid and semi-arid areas. A RWHI system has three main components, i.e. rainwater/runoff collection catchment, rainwater/runoff storage facility, and a low-cost irrigation system that applies water to the crop area during dry periods. Best practices for RWHI management at household level are upgraded on-farm ponds and/or low-cost roof catchments connected to manual pumping systems and low-cost drip irrigation kits. Total costs for storage capacities of 50–100 m3 range from 1000 to 3000 USD and present cost-efficiencies of 26–50 USD/m3 of irrigated water. At community level, hillside earth dams, rock catchments, alluvial shallow groundwater, subsurface dams and sand storage dams can be connected to mechanised/manual pumping systems and low-cost drip irrigation kits. RWHI systems which use subsurface dams made of soil present the highest cost-efficiency (3 USD/m3 of irrigated water). Further, RWHI technologies are clearly site-specific. Therefore, replication and scaling-up needs to strictly consider multi-dimensional physical and hydrogeological suitability factors coupled with the cost-efficiency and specific technical considerations of the technologies and practices. In addition, the technical and financial capability of the beneficiaries coupled with the revenue potential of the RWHI systems plays a crucial role in the replication of RWHI technologies.