- 1 What is groundwater used for?
- 2 Estimating groundwater use
What is groundwater used for?
Groundwater is the main source of water for drinking, cooking and sanitation for most people in Africa - not just the rural population, but also much of the urban population. Most groundwater is abstracted directly by the users from low yielding, relatively shallow (usually less than 50 m deep) boreholes or hand dug wells. Deeper, higher yielding boreholes are less common, but are used in many urban areas to provide piped municipal water supplies.
Evidence suggests the use of groundwater to support economic livelihood activities in Africa is growing - particularly agriculture and industry. This is almost all at a small scale - by individuals or communities, such as to support market garden irrigation or local food or drink businesses.
However, as discussed below, it is very difficult to estimate how much groundwater is being used in Africa, and for what purposes.
Estimating groundwater use
Many attempts are made to estimate how much groundwater is 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, these estimates are difficult to do, and there is much variation between different estimates. This is largely because groundwater use is highly dispersed, both from improved (e.g. community boreholes) and unimproved (e.g. springs or hand dug wells) sources. It is therefore very difficult to directly measure how much groundwater is abstracted and used, and for which purposes. Even if data are collected, there are often problems in recording, managing and accessing the data.
Nevertheless, these estimates are very useful, not only in trying to quantify demand in order to better balance against groundwater resources and therefore support groundwater development, but also in highlighting the value of groundwater.
The following are some of the main sources of groundwater use estimates for Africa.
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 AQUASTAT country profile contains general information on the geographical and economic situation of the country, and more detailed information on surface water and groundwater resources, water use (with a particular focus on irrigation), and water management.
The AQUASTAT database reports water statistics at a country level, with a special emphasis on irrigation and agricultural water. The statistics are based on the best available data and analysis techniques, but even so, there are data gaps for many countries. These gaps are often worse for groundwater, because groundwater use for agriculture is more difficult to measure directly. Large scale irrigation schemes, which are easier to measure, are usually based on surface water. By contrast, groundwater-based irrigation and other agricultural use is dominantly small-scale and managed by individual farmers or communities, and so is very difficult to measure and record.
AQUASTAT uses modelling to fill in some of these data gaps, including to estimate irrigation water withdrawal. This allows useful comparison between countries - but it must be recognised that these data may not be accurate.
Groundwater use for irrigation
Seibert et al. (2010) provide an estimate of the amount of groundwater used for irrigation in Africa.
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.
An estimate of rural groundwater use in Africa using population data
Because most of the rural population of Africa depends on groundwater, the density of rural population can be a useful surrogate for groundwater use.
[MacDonald and Davis (2000) assessed the relative importance, in terms of groundwater use, of the four main hydrogeological provinces in sub-Saharan Africa, based on estimates of 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 in sub-Saharan Africa.
This assessment has been extended over the entire continent of Africa, and re-calculated based on the updated hydrogeology map of Africa developed by BGS. 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 study estimates that:
- up to 335 million people live in rural areas on basement rocks – around 30% of the total population of Africa
- up to 340 million people live in rural areas on consolidated sedimentary rocks – around 31% of the total population of Africa. This can be further subdivided based on the dominant groundwater flow mechanism in the sedimentary aquifers : fracture flow (up to 146 million); intergranular flow (up to 79 million); and mixed fracture and intergranular flow (up to 114 million)
- up to 99 million people live in rural areas on igneous rocks – around 9% of the total population of Africa
- up to 142 million people live in rural areas on unconsolidated rocks – around 13% of the total population.
The gridded population data were derived from the United Nations Environment Programme/Global Resource Information Database (UNEP/GRID) African Population Distribution Database (4th edition). This dataset used population data from 109 000 administrative units across Africa, the most recent of which were compiled for the year 2000. The regional data were gridded using an interpolation method based on settlement locations and transport infrastructure, which helps to distribute the population across an administrative area.
The gridded rural–urban population data (Balk et al., 2006) were derived from the Global Rural-Urban Mapping Project (GRUMP) Urban Extents Grid (v1). This dataset was 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.
Balk, D L, Deichmann, U, Yetman, G, Pozzi, F, Hay, S I, 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 Project, Version 1 (GRUMPv1): Urban Extents Grid. Palisades, NY: NASA Socioeconomic Data and Applications Centre (SEDAC). Accessed 30th October 2014.
MacDonald, A M, Davies, J. 2000. A brief review of groundwater for rural water supply in sub-Saharan Africa. British Geological Survey Technical Report, WC/00/033 (Unpublished).
Seibert, S, Burke, J, Faures, J M, Frenken, K, Hoogeveen, J, Doll, P, and Portmann, F T. 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. Note: the African Population Distribution Database was retrieved on 29 October 2014, but is currently not available. Information on UNEP's population datasets is available at http://www.un.org/en/development/desa/population/publications/database/index.shtml