Researchers estimate the total groundwater storage in Africa to be 0.66 million km3. "Not all of this groundwater storage is available for abstraction, but the estimated volume is more than 100 times estimates of annual renewable freshwater resources on Africa," says lead author Dr Alan MacDonald.
The researchers, from the British Geological Survey and University College London, warn that high yielding boreholes will not be found using a scattergun approach and a more careful and exploratory approach that takes into account local groundwater conditions will be needed.
In many populated areas in Africa, there is sufficient groundwater to supply hand pumps that communities can use for drinking water where 300 million people do not have access to safe drinking water. These hand pumps can deliver around 0.1-0.3 litres per second. Opportunities for boreholes yielding five litres per second or more - the usual amount needed for commercial irrigation - are not widespread and limited to specific areas, such as countries in the north of Africa.
Central to the researchers' methods was the collation of existing national hydro-geological maps as well as 283 aquifer studies from 152 publications. The vast amount of data was compiled into a single database in which the researchers were able to make their calculations.
The amount of groundwater present in a certain region is reliant on the interplay between the geology of the area, the amount of weathering and the amount of rainfall experienced both in the past and present. All of these factors were considered to estimate the volume and potential yield of groundwater in each aquifer.
As a result of population growth in Africa and a planned increase in irrigation to meet food demands, water use is set to increase markedly over the next few decades. Climate change will pose a huge threat to this increase; however, groundwater responds much more slowly to increasing climatic variability as opposed to surface water, so will act as a buffer to climate change.