KAREN VILLHOLTH
Good understanding of climate change is needed in Africa
In 2014-2016, southern Africa saw its worst drought in decades, resulting from the most severe El Niño event in half a century. Leading to sharp declines in crop production, the drought dealt a severe blow to food security, with millions across the larger Pacific region facing hunger, poverty and disease. While we all know groundwater is a key water resource for farmers, small communities and larger cities alike in sub-Saharan Africa, it is largely missing from existing analysis of climate change impacts on water. Yet, Cape Town, which was greatly supported by groundwater development in its struggle to push back Day Zero when the city was projected to run out of water, shows us that groundwater is key to resilience. But how does this unseen and relatively untapped resource in sub-Saharan Africa itself react to climate change?
This may be the ultimate question as our water resources are finite, increasingly scarce and increasingly in demand. If African countries are to rely on groundwater for future resilience and manage it sustainably, they must quickly gain a better understanding of climate change impacts on this critical resource. A recent study sheds new light on the climate-groundwater relationship, finding that the 2015-2016 El Niño weather event replenished groundwater very differently in southern Africa and in East Africa just below the equator. Based on a combination of satellite and on-site data analysis, it is part of a growing body of research, to which the International Water Management Institute (IWMI) is contributing, in collaboration with UK partners such as University College London, Cardiff University, University of Sussex, and British Geological Survey, as well as others in southern and eastern Africa.
The El Niño-Southern Oscillation, or ENSO phenomenon, involves the interaction between the atmosphere and the ocean in the tropical Pacific. It is a telling cause of climate variability in the tropics. As an extreme case among historical patterns, the 2015-2016 event had exactly opposite effects on rainfall in southern Africa and East Africa below the equator. In southern Africa, it resulted in the most intense drought ever recorded for the region, estimated to recur every 200 years. The authors note that warming caused by human activities has heightened climate risks. They suggest that this has already “doubled the risk of such an extreme… event,” meaning such an intense drought could return every 100 years.
The 2015-2016 drought limited the recharge of aquifers and increased demand for groundwater leading to a decline in groundwater storage. In contrast, East Africa, just south of the equator, saw unusually high – but not extreme – rainfall, likely to recur every 10 years. With 100-150% above normal daily rainfall intensity in many places, this significantly boosted groundwater recharge and storage. At the Makutapora well field in Tanzania, for example, strong groundwater recharge reversed a long-term decline in groundwater storage that had resulted from increasingly intensive pumping to the growing city of Dodoma. Another new study published in Nature underpins the importance of extreme rain events in restocking groundwater in dry lands in sub-Saharan Africa. Rather than being replenished through regular rainfall, groundwater responds best to extreme rainfall – the type that happens every 10 years or so.
