3.4.2.3 Improving water supply through effective capture of water flows and use of marginal water resources Throughout SSA, pockets of suitable land, water and fisheries could be used more sustainably. Current AKST can tap this potential.This will require technology for water storage, rainwater harvesting, exploitation of aquifers, interbasin water transfers, desalinization, wastewater use, and sustainable and wise use of wetland and forest ecosystems. The challenge lies in creating the conditions for sustainable use of these resources by acquiring use rights and improving market access, incentives and regulation.

The productivity of rainfed agricultural systems in many parts of SSA is low and there is considerable potential for increasing it through AKST. Grain yield in semiarid Africa can be increased from the current 0.5 to 1 tonne to 5 tonnes ha-1 by increasing the green water (water from precipitation stored in unsaturated soils) taken up by plants as evapotranspiration (Rockstrom, 2001). The largest improvement in yield and water efficiency is achieved by combining supplemental irrigation with fertilizer application. Water conservation practices that increase available soil moisture can be economically feasible only when nutrient deficiencies are corrected (Onken and Wendt, 1989). Studies on deficit irrigation have shown that applying less than optimal amounts of water can increase productivity (Oweis and Hachum, 2001).

Improving the water supply in rainfed agriculture is required to unlock its potential. Maize yields of resource-poor farmers are generally less than 1 tonne ha-1, whereas farmers who adopt modern technologies (improved seeds, fertilizers, etc.) obtain 1.5 to 2.5 tonnes ha-1 (Rockstrom et al., 2007). This is partly because of high runoff and evaporation losses. Where AKST has been adopted, soil water is enhanced and crop performance improved. Mulching in a semiarid environment can increase maize by 35 to 70% (Liniger et al., 1998). In northern Ghana the improved access, adaptation and adoption of soil and water conservation techniques— stone bunding, mulching, water harvesting, composting and planting neem, acacia and mango trees—contributed to a maize yield increase from an average of 0.200 tonnes ha-1 to 1.600 tonnes ha-1. A combination of soil and water conservation practices, fertilizer micro-dosing and an informal inventory credit system that secures a fair price for produce and improves access to inputs has improved the livelihoods of over 12,000 farmers (Tabo et al., 2005). Yields of sorghum and millet increased 44 to 120% while farmer income increased 52 to 134%.

Water harvesting and storage reduces the risk of crop failure. Under such conditions, farmers use few purchased inputs, which further limits attainable yields, even in good rainfall years. Such farming strategies are partly responsible for the low adoption of high-yielding technology, improved management and other AKST. Improved moisture conservation reduces runoff and soil loss, reducing the frequency of water stress on crops. Water harvesting has been shown to reduce risk by 20 to 50%. Small reservoirs and soil and water conservation practices reduced risks associated with climate variability, facilitated the adoption of higher-yielding crop varieties, increased fertilizer use and produced a timelier and better crop (Faulkner, 2006). These improvements

led to better resource efficiency, a 40 to 160% increase in maize yield and a 30 to 85% increase in profitability. Expansion of cropland and higher yields are curtailed by the inability to harvest and store rainwater and manage it to enhance biomass.

The strategic placement of livestock watering points facilitates the use of grazing resources that would ordinarily have gone to waste. In the Wajir district of Kenya, 10 to 50% of the grazing resources are underused because livestock lack water points. About 15 to 35% are severely degraded because of livestock concentration around the watering points. Considering the growing demand for livestock products in SSA, enhancing livestock water supply in underutilized grazing areas is highly desirable.

Studies on urban agriculture report the high potential for wastewater irrigation, partly because it has many nutrients and the area that would be watered is close to the market. In Accra, over 800 small vegetable farmers produce vegetables using wastewater. These vegetables, mainly lettuce, are consumed by about 200,000 urban dwellers but could pose a considerable health risk (Obuobie et al., 2006).

3.4.2.4 Fair sharing and benefits from water use
All SSA countries share at least one international river basin and natural transboundary flows are significant in some countries. Not only does the water have to be shared among sectors, it has to be shared among countries. The benefits from water use vary, with higher values seen where there is a comparative advantage. Maximizing the total net benefit from a shared water basin requires planning and an evaluation of the tradeoffs between optimizing total net benefit and enhancing local self-sufficiency.

There is considerable scope to improve the performance of irrigated agriculture. Approximately 40 to 60% of irrigation water in SSA is lost through seepage and evaporation and seepage contributes to soil salinization and waterlogging (UNEP, 2002). Irrigation and drainage projects in semiarid areas are at risk from poor operation and maintenance. The high sediment load in most rivers chokes intake works and silt is deposited in canals and reservoirs, reducing capacity and making water control structures inoperable. As a consequence, systems operate below capacity and have unreliable supplies, which result in reduced cultivated area, yield decline, farmers shifting to lower-value crops, fewer inputs to reduce risks and reduced investments in maintenance. As a result, small-scale farmers and some government irrigation projects undergo cycles of build–neglect–rehabilitate– neglect and some are ultimately abandoned.

Good maintenance practices can generate positive incremental benefits even under adverse conditions (Skutsch and Evans, 1999). In order to improve maintenance, irrigation planners and managers and policy makers must create policy and institutional frameworks and provide incentives conducive to improved design, planning and operations (IPTRID, 1999).

3.4.3 Biodiversity
Natural ecosystems provide many services essential to human existence (Jackson et al., 2007). Increased species diversity provides more opportunity for species interactions,