Drought Management Strategies | Water Harvesting, Water Storage, and Supplemental Irrigation
Agriculture accounts for about 70–75% of global water withdrawals. About 20% of the world’s farmed area is irrigated, and produces 40% of the value of agricultural production in developing countries (World Bank’s Agriculture Action Plan).
Approximately 60% of agricultural production in developing countries is rain-fed, making water availability and efficient management key determinants for agricultural production, particularly in arid and semi-arid regions. Therefore, investments in irrigation infrastructure will continue to be critical for unleashing agricultural potential in much of the developing world.
However, many farmers are unable to irrigate because they lack an adequate water source. Surface water sources, such as streams, often do not have sufficient flow during the growing season to provide irrigation water. And, in many areas of the world, ground water sources are either inadequate or impractical to develop for irrigation.
An alternative approach to securing irrigation water is to collect and store surface water during the off-season, when rainfall and stream flows are high. This practice is called water harvesting, which can be used for several purposes (including irrigation). At the farm level, techniques for harvesting water include: harvesting rainfall water from rooftops and other surfaces to be distributed to fields through gravity or pumping methods, and building reservoirs and other low-cost storage facilities.
These methods are complemented with the application of supplemental irrigation methods – using only one-third the water required for full irrigation – on primarily rain-fed crops, farmers can boost their yields by more than double (International Center for Agricultural Research in the Dry Areas—ICARDA). Supplemental irrigation in areas with limited water resources can be applied i) to a rain-fed crop that would normally produce some yield without irrigation, ii) only when precipitation fails to provide essential moisture for improved and stabilized production, and iii) only to ensure that the minimum amount of water required for optimal (not maximum) yield is available during the critical stages of crop growth. An example of this practice is an ICARDA-led project in Morocco in which early planting combined with supplemental irrigation and improved wheat varieties doubled wheat yields and water productivity. In Rwanda, the World Bank implements the Land Husbandry, Water Harvesting and Hillside irrigation project, which represents an example of investments in watershed management to increase availability of water to crops.