“In Africa, groundwater is the major source of drinking water and its use for irrigation is forecast to increase substantially to combat growing food insecurity,” yet, a lack of quantitative data has meant that “groundwater storage is consequently omitted from assessments of freshwater availability,” according Alan Macdonald
, Helen Bonsor
, and Brighid Dochartaigh
of the British Geological Survey, and Richard Taylor
of University College London, writing in Environmental Research Letters
The authors hope to remedy this with new research presented in “Quantitative Maps of Groundwater Resources in Africa.” They used estimates compiled from geologic data and 283 aquifer summaries from 152 different publications to quantitatively visualize, for the first time, the full extent of Africa’s groundwater resources.
Tapping a Hidden Resource
The study estimates the scale of the continent’s groundwater resources at around 0.66 million km3. This volume, the authors explain, is “more than 100 times the annual renewable freshwater resources, and 20 times the freshwater stored in African lakes.”
Tapping into this massive resource is not always straightforward, however. The largest aquifers, and those most able to support high yielding bores, are concentrated in the arid regions of North Africa. The depth of these aquifers and their distance from major populations creates substantial economic challenges for extraction.
The geographic distribution of aquifers across sub-Saharan Africa is also quite variable, and local geology can determine not just the availability and accessibility of water but also its quality. For instance, geologic specificities can result in elevated levels of arsenic and other undesirable chemicals. Furthermore, “contamination…is common in urban areas from widespread and dispersed faecal effluent from on-site sanitation and leaking sewers.”
Throughout Africa, “groundwater provides an important buffer to climate variability and change,” say the authors. But these buffers are not a singular solution to the threat of future water scarcity.
As the analysis shows, most aquifers, especially south of the Sahara, are unlikely to sustain boreholes of a higher capacity than that required by community-level hand pumps (one liter per second of flow at minimum). Yet, commercial irrigations schemes and urban towns typically demand boreholes greater than five liters per second, according to the study.
So, groundwater extraction may help communities and some small-scale farmers maintain access to water, particularly because many aquifers are found to possess the storage capacity required “to sustain abstraction through inter-annual variations in recharge,” however, “strategies for increasing irrigation or supplying water to rapidly urbanizing cities that are predicted on the widespread drilling of high yielding boreholes are likely to be unsuccessful.” Especially, the authors assert, where drilling precedes detailed local scale mapping of the available resources.
Sources: Environmental Research Letters.
Image Credit: Figures 1 and 3, courtesy of Environmental Research Letters.