Africa's underground oceans

Oceans cover approximately 70% of the world, with 97% of world's water held in oceans. To put that into easier figures, there are 332,519,000 miles3 of water on earth, or 352,670,000,000,000,000,000 gallon-sized milk containers. Facts like these are easy to find (NOAA, 2015), but these figures hide the importance, necessity and access to water across the human-inhabited world, i.e. not the ocean. 

To get a better understanding of the volume of water on Earth, the images from Randall Munroe's online question blog give a good understanding of how much of Earth's land mass is covered by water.

Sea level decrease of 5km (Munroe, 2013)

Freshwater only accounts for 3% of all the water on Earth. The temporal and spatial distribution of freshwater however tends not to match the temporal and spatial distribution of human populations. Therefore, some regions of Earth are known to be water stressed, where the availability of water is not always where it is required.

Until recently, the total volume of Africa's groundwater supply was unknown.

Simplistic older hydrological models in Africa would identify one figure for infiltration and assume that covered the groundwater interaction (Kutzbach, 1980). Although this method is useful if looking at above-surface hydrology, there are sub-surface interactions that can further impact the hydrology of a basin further than being an 'output'.

MacDonald (et al., 2012) provides insight into the stored capacity of groundwater across Africa. The article estimates there to be 0.66 million km3 of freshwater capacity in Africa, with the greatest reserves in Northern Africa, and potential yields of certain regions. MacDonald (unclearly) claims that due to low transmissivity in Sub-Saharan Africa, the geology is limited for intensive irrigation. However, groundwater abstraction is still possible in Sub-Saharan Africa in areas of low water demand.

Groundwater storage with rechargein Africa
(water depth in mm) (MacDonald et al., 2012)

Although MacDonald's (et al., 2012) work is highly beneficial to international aid and development networks, there is a warning that it does not discuss. Groundwater can have a long recharge rate, especially with increasing population and more intensive abstraction. Hence, careful planning by researchers, governments and local communities should be undertaken in order to sustainably mine Africa's underground ocean.