Mapping the Potential of Rainwater Harvesting for Africa and Nine Selected Countries
Water is at the heart of Millennium Development Goals (MDGs) numbers 1, 3 and 7, and is indirectly associated with the success or otherwise of all the other Goals. But for Africa to meet the MDGs, bold and targeted actions will be required in the water sector. Given that about 300 million people in Africa - a third of the continent’s population - are living under “water scarcity” situations, urgent action is required else 12 more African countries will join “water scarce” nations by 2025.
To address this, the African Water Vision for 2025 is set to develop the full potential of Africa’s water resources for sustainable growth in the region’s economic and social development, of which rainwater harvesting (RWH) and storage forms a major component. Among others, the Vision calls for “improving water wisdom”, which is to be achieved by establishing an elaborate system of data collection, management, dissemination, including standardization and harmonization of data and information.
Towards this end, data sources have been developed such as FAOSTAT, AQUASTAT and Agriculture towards 2015/30. Continent-wide spatial information on rainwater harvesting potentials in Africa has, however, been lacking. This information is necessary to raise world-wide awareness and guide policy decisions on the contribution of rainwater harvesting (RWH) towards meeting MDGs, the African Water Vision and generally, the water needs of men and women in Africa, for improved livelihoods and ecosystems. UNEP and ICRAF are member s of the Rainwater Partnership w h o s e objective is to promote the use of rainwater by ma i n s t r e ami n g the resource into Integrated Water Resource Management (IWRM). To meet the growing demand for broad scale spatial data on rainwater harvesting in Africa, UNEP and ICRAF embarked on developing a tool for mapping rainwater harvesting potential at national, regional and plot scales. This work started in 2005 and culminated in a book titled ‘Mapping the potential of Rainwater Harvesting for Africa and nine selected countries.
This technical report thus shows in spatial domains, the expansive opportunities for RWH in Africa and the following countries; Botswana, Ethiopia, Kenya, Malawi, Mozambique, Tanzania, Uganda, Zambia and Zimbabwe. It produced a GIS database that captures the major factors associated with RWH (rainfall, topography, soils population density, land use). These baseline thematic maps were further combined through spatial analyses to produce composite maps that show attributes or “development domains” that serve as indicators of suitability for targeted RWH interventions, grouped as; (i) rooftop RWH, (ii) surface runoff from open surfaces with storage in pans/ponds, (iii) flood-flow harvesting from watercourses with storages in sand/subsurface dams and (iv) in-situ soil water storage systems. Consequently, the project produced a total of 73 maps, which comprise 29 thematic base maps, maps covering Africa and 44 composite thematic maps for the nine country case studies.
These maps provide a broad-brush, exploratory scale decision-support tool, since the GIS input data used was of low resolution at continental scale. Noting that the major ingredient in rainwater harvesting is rainfall, and guided by the fact that if it rains, it can be harvested regardless of the quantities (too little or too much), the authors have, therefore, avoided labeling areas as either suitable or unsuitable for RWH.
The decision of final prioritization is left to the user after analyses of other factors beyond the GIS database such as finances, cultural, political and local preferences. The tables below show the harvestable runoff water for medium rainfall (400-1200mm), gently sloping (2-8 per cent) domain for all the nine countries and populations these domains can sustain. These are supported by examples of selected maps.
For more information on the potential of other rainwater harvesting domains such as in-situ and domestic water, please contact the under mentioned:
Programme Officer - Information ICRAF Water Management Unit
World Agroforestry Centre TRANSFORMING LIVES AND LANDSCAPES
International Centre for Research in Agroforestry
United Nations Avenue
P.O. Box 30677 -00100, Nairobi, Kenya
Tel: +254-20-722 44 24 (Direct)
+254-20-722 40 00 (Operator)