Estimating Groundwater Use
Many attempts have been made to estimate how much groundwater is being used in Africa, at local, national and international scales - and also to estimate how many people depend on groundwater, and the kinds of activities that groundwater supports. However, because groundwater use is so varied and dispersed, and because of the problems that exist in collecting, recording, managing and accessing information on groundwater use, these estimates are difficult to do, and it isn't always clear how reliable they are.
FAO AQUASTAT is the FAO’s global water information system, providing data for countries in Africa, Asia, Latin America, and the Caribbean. It is widely used as a source of information on groundwater use. Each country profile contains general information on the geographical and economic situation of the country, and more detailed information on water resources (major sources of surface water and groundwater), water use (with a particular focus on irrigation), and water management.
WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation
The WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation is ongoing and provides summary statistics for water supply and sanitation coverage. This includes an estimate of groundwater use for drinking water.
Groundwater use for irrigation
Seibert et al. (2010), provided an estimate of the amount of groundwater used for irrigation in Africa.
Estimating groundwater use using rural population data
Because a very high proportion of the rural population of Africa depends on groundwater, the density of rural population can be a useful surrogate for groundwater use.
MacDonald & Davis (2000) assessed the relative importance of the main hydrogeological provinces in sub-Saharan Africa based on the rural population living in each one. They estimated that up to 220 million people live on Precambrian basement, 45 million on volcanic rocks, 110 million on consolidated sedimentary rocks, and 60 million on unconsolidated sediments.
This assessment has been extended over the entire continent and re-calculated based on BGS’ updated hydrogeology map of Africa. Gridded datasets of population and urban extent across Africa were processed to provide an estimate of the number of people living on each main aquifer type, and what proportion of this population lives in rural and urban areas. Details of the datasets are provided below.
The analysis shows that:
- up to 335 million people live in rural areas on basement rocks, accounting for around 30% of the total population of Africa;
- up to 340 million people live in rural areas on consolidated sedimentary rocks. This accounts for 31% of the total population of Africa and can be further subdivided based on the dominant flow mechanism in the rock
- fracture flow (up to 146 million), intergranular flow (up to 79 million), and fracture and intergranular flow (up to 114 million);
- up to 99 million people live in rural areas on igneous rocks, accounting for around 9% of the total population of Africa; and
- up to 142 million people live in rural areas on unconsolidated rocks, accounting for around 13% of the total population.
The gridded population data are derived from the United Nations Environment Programme/Global Resource Information Database (UNEP/GRID) Africa Population Distribution Database (4th edition). This dataset uses population data from 109 000 administrative units across Africa, the most recent of which were compiled for the year 2000. The regional data are gridded using an interpolation method based on settlement locations and transport infrastructure, which helps to distribute the population across an administrative area. The gridding approach and the key sources of uncertainty in the dataset are discussed in detail in the data documentation (Nelson, 2004).
The gridded rural-urban data (Balk et al., 2006) are derived from the Global Rural-Urban Mapping Project (GRUMP) Urban Extents Grid (v1). This dataset is produced by the Centre for International Earth Science Information Network (CIESIN) at Columbia University, the International Food Policy Research Institute (IFPRI), The World Bank, and the Centro Internacional de Agricultura Tropical (CIAT). The dataset is based on a combination of population counts, settlement points, and the presence of night-time lights as observed by a series of US Department of Defence meteorological satellites over several decades.
Citations and Links to Further Information
Balk, DL, Deichmann, U, Yetman, G, Pozzi, F, Hay, SI, and Nelson, A. 2006. Determining Global Population Distribution: Methods, Applications and Data. Advances in Parasitology, Vol. 62, 119-156. doi:10.1016/S0065-308X(05)62004-0.
CIESEN, IFPRI, The World Bank and CIAT. 2011. Global Rural-Urban Mapping Projectm Version 1 (GRUMPv1): Urban Extents Grid. Palisades, NY: NASA Socioeconomic Data and Applications Centre (SEDAC). Accessed 30th October 2014.
MacDonald AM, Davies J. 2000. A brief review of groundwater for rural water supply in sub-Saharan Africa. British Geological Survey, 30pp. (WC/00/033) (Unpublished)
Seibert S, Burke J, Faures JM, Frenken K, Hoogeveen J, Doll P & Portmann FT. 2010. Groundwater use for irrigation - a global inventory. Hydrol. Earth Syst. Sci. 14, 1863-1880. doi: 10.5194/hess-14-1863-2010
UNEP/GRID. 2004. African Population Distribution Database. UNEP GRID Sioux Falls. Retrieved 29th October 2014.