New insights into the future of water availability in Southern Africa

New research suggests that extreme future drying over southern Africa is an unlikely scenario, but that regional governments should still prepare for a water-stressed future.

By Callum Munday

In the summer of 2015, southern Africa experienced one of its worst droughts on records. Water supply for major cities, including Cape Town (South Africa) and Gabarone (Botswana), was running low; crops had failed; and electricity generation from hydropower was at a minimum. The spectre of climate change loomed large: was this a sign of things to come?

Yes, according to the Intergovernmental Panel on Climate Change (IPCC)’s climate models. Ninety-five percent of these models indicate, at least for the early summer season, that southern African rainfall will decline significantly by 2100. Some models project average rainfall declines of close to 100 mm per season—similar to the rainfall anomaly during the summer 2015 drought. If these extreme projections are to be trusted, adaptation to future climate change will need to be fast and effective.

However, climate models are not perfect. Rainfall simulation is a particularly tricky task with longstanding and well documented errors in southern Africa. A key question for climate scientists is whether these errors in model simulations of present-day climate matter for how they project future change.

In a new study in Journal of Climate (Munday and Washington 2019), we address this issue by examining the mechanisms associated with future southern African rainfall/drying changes during the early summer in models. We found broad consensus between models in how they simulate climate change, with the rainfall declines linked to increases in the stability of the southern African atmosphere.

However, by splitting up models into groups according to how much rainfall decreases in the future, we found that models simulating the largest average rainfall declines (close to the 2015 anomalies) contain substantial errors in how they simulate the present day climate. This insight casts doubt on projections of extreme rainfall decreases and suggests that more moderate drying is the more likely scenario1.

Given the effects on southern African society, the evidence that really extreme drying is unlikely is welcome, but there remains a raft of challenges facing regional governments. Temperatures in southern Africa are expected to rise at twice the rate of the global mean, and droughts—when they do happen—could become more intense and prolonged. Preparing for a more water-stressed future, unfortunately, remains a priority for southern Africa.

1Another study which uses a different methodology (Padrón et al., 2019) also concludes that extreme projections of drying over southern Africa are unlikely.

Callum’s research was funded by the UK Natural Environmental Research Council (NERC). It was carried out as part of the Future Climate for Africa UMFULA project, with financial support from the NERC [Grant ref: NE/M020207/1], and the UK Government’s Department for International Development (DFID).