Borehole in Tanzania (Credit: Tumaini Fund)
On the 25th October, Laura Hunt (Cardiff University) attended the joint meeting of the International Association of Hydrogeologists (IAH) and the Hydrogeological Group of the Geological Society, which included the Ineson Lecture at the Geological Society of London.
It is a common misconception that Africa is an entirely dry, arid continent, parched for water. A resource that we in the UK take almost for granted, but that we assume all across Africa is hard to come by, with women walking many miles a day for drinking water, which is for the most part polluted with toxins and waterborne diseases. And for many communities, in many countries within Africa, this unfortunately is the case; the lack of surface water is a barrier to social and economic development.
But Africa is also a resource rich continent in terms of water. The continent has a huge groundwater resource, including large transnational aquifers. The exploitation of this incredible resource could be the key to facilitating Africa’s development, and coping with its rapidly increasing population.
Increasingly, investment in Africa’s water resources from NGOs, charities and private firms is in boreholes to extract clean groundwater. However, with anthropogenic driven climate change in this century and beyond predicted to be most adverse and rapid in the lowest (and highest) latitude regions, it’s important to understand the implication of a (overall) warmer and wetter world on this important resource prior to huge investment and increased dependency of many vulnerable countries upon it.
At the IAH conference, which I was lucky enough to attend with support from Geology for Global Development, University College London’s Richard Taylor spoke of his work aiming to answer this question with use of the ‘Chronicles Consortium’ – a collaboration of many groundwater resource’s multi-decadal hydrographs from a number of African countries to understand the response of aquifers to short term climatic events.
Africa is a vast continent with huge contrasts in climate between regions, and so climatic changes will not be unilateral across the continent, hence leading to different impacts on distant groundwater resources. The 2015/2016 El Nino event which was the second strongest event experienced for 150 years lead to contrasting impacts on the water balance across the continent. The Limpopo Basin (central southern Africa) experienced dry conditions, enhancing aridity in the area, whereas Northern Mozambique experienced wetter weather, with groundwater recharge recorded at 2000 boreholes.
The ENSO (El Nino Southern Osscilation) evidently had a strong influence upon groundwater recharge in some areas. In central Tanzania. Despite increased rates of pumping from the aquifers in the Makutapora basin (ie decline in water), ground water levels still rose.
The mechanism and conditions for recharge to occur is important in understanding the response of climatic change. Recharge velocities associated with the application of the regular diffuse model to recharge of the Makuapora Basin are simply inadequate to account for the rates of recharge recorded. However a mechanism of recharge focused pathways that focus diffuse recharge allow for faster infiltration and recharge of groundwater. These recharge pathways are the major, domain component of groundwater recharge as they are so focused compared to diffuse infiltration, but are only realised (utilised). Approximately 5-15mm of rain per day is required for 5-13 days are required for recharge to occur.
It can therefore be concluded that recharge occurs episodically and results disproportionately from heavy rainfall events.
So what are the implications of the changes in climate that we are already seeing and will continue into and beyond the 21st Century and beyond on these ground water resources? The key to sustainability is that development and investment should benefit future generations and so we need to make sure that this resource is viable for the future.
Firstly, climate change will lead to increased aridity around the equator, but enhanced rainfall around the tropics, creating disparity in the health of aquifers across the Africa.
Around the tropics, precipitation is expected to be less frequent but more intense, and so the threshold required for recharge is likely to be met, and so recharge will be greater (along with increased frequency of flooding events).
However, heavy rainfalls and increased macrogenic flow of water in the soil zone leads to greater contamination of shallow waters and are more vulnerable to pathogen transfer. Antecedant conditions also have a significant control over water quality with dry antecedent conditions leading to lower water quality with the highest degree of contaminiation than if antecedent conditions are wet. If climatic change causes more intense precipitation, and less gentle rainfall events, groundwater in regions of recharge are likely to become increasingly contaminated.
This research is just the beginning of understanding and predicting the response of the water table to climatic change, but allows us to begin to understand what challenges will be faced by Africa’s hydrogeologists and water authorities. This incredible resource with the power to drive Africa’s development, if chosen to be located in areas where overall long term recharge will occur, can be managed to reduce the effects of enhanced contamination and therefore provide a reliable and safe drinking water supply to some of the people most vulnerable to anthropogenic driven warming. With management of disease spread that was also showcased at the IAH conference by Cambridge University, it seems that there is the potential for a positive future for some African countries water resources to be revolutionised by the use of ground water. And this can be done sustainably – so long as the right long term management and planning, and of course further research is implemented.
This post is a guest contribution, sharing initial thoughts of a student attending the Ineson Lecture (and associated meeting) in London. For further information about the event, please see the event webpage and contact the speakers directly.
