South Africa’s foremost climate experts met at the Department of Rural Development and Land Reform in Cape Town yesterday to deliberate on the possibilities that the 2017 winter season in the Western Cape region may be drier than normal or relatively normal – neither of which will alleviate the current low reservoir levels.
The experts – representing the Alliance for Collaboration on Climate and Earth Systems Science (Access), in collaboration with a host of organisations including local and provincial government – agree that the extremely low reservoir levels are at least partly a result of an accumulated 2-3 years of relatively low winter rainfall.
“The current drought is a combination of a decrease in previous years’ rainfall and an increased demand for water,” said Access director Dr Neville Sweijd who chaired the one-day summit.
“The model might say that there is a 52% chance of relatively high rainfall this season, but our confidence in that 52% might be very low, therefore there is no definitive story to tell about this season’s rainfall.”
Additionally, the experts gathered yesterday agree that it will take more than one season to completely replenish the deficit of surface water reserves in the region.
It is important to note that seasonal cycles and natural cycles of relatively wetter and drier winters will continue.
However, experts warn that there is a weight of evidence provided by a large body of published research that has been assessed by the Intergovernmental Panel on Climate Change which supports the reasonable expectation of a relatively drier �Western Cape by the 2030s and 2040s.
There is little doubt that the Western Cape needs to prepare, in the longer term, for a drier climate.
“The skill needed to make a forecast for the next winter rainfall season is at best marginal,” says CSIR chief researcher Professor Francois Engelbrecht, “There is a fair level of consensus among the models used, but the long-term demonstrable success in these forecasts is low.
"We predicted that the Vaal Dam would fill up again, and we were correct. It is possible that the season will be exceptional in terms of rainfall, but there are no forecasts saying that, so the likelihood is low,” said Engelbrecht.
The science of Seasonal Climate Prediction (SCP) has been applied in South Africa with moderate success in the north-east of the country’s summer rainfall region, but is limited and constrained in its efficacy to only certain climate conditions and periods.
And given that the Western Cape is a winter rainfall region with dry summers, the challenge is therefore to develop a robust system for the prediction of the extent of winter rainfall and its likely departure from the long-term averages.
However, currently no such seasonal forecast system – locally or internationally – exhibits any significant skill in predicting winter rainfall for the Western Cape.
A collaborative research effort is currently under way to further improve the skill of SCP in southern Africa and in the sub-regions and respective climate zones.
It is currently impossible to produce a scientifically defensive and robust prediction of the seasonal winter rainfall for the Western Cape.
It is the experts’ view, thus, that the Western Cape needs to prepare for the possibility that this year’s winter season may be drier than normal, which may greatly exacerbate the current situation; or it may be relatively normal, which will fail to relieve the current situation.
Tendani Tsedu,
CSIR Group Manager:
Strategic Communications