Scientists at two American institutions, Stanford University and the National Oceanic and Atmospheric Administration (NOAA), have warned that climate change caused by human activities has greatly increased the probability of Cape Town being again afflicted by very severe droughts such as that experienced by the city from mid-2015 to mid-2018. From late 2017 to mid-2018 there were fears that the water levels in the city’s dams would fall so low that Cape Town would effectively run out of water, a scenario that was known as ‘Day Zero’.

The Stanford and NOAA researchers came to this conclusion after running new simulations using the Seamless System for Prediction and Earth System Research (Spear) climate modelling system. Spear allows the creation of climate models that have a higher resolution than previously possible. The results suggest that the probability of future ‘Day Zero’ scale droughts in south-western South Africa, including Cape Town, could increase five- or six-fold, and become common by the end of this century.

“In a way, the ‘Day Zero’ drought might have been a sort of taste of what the future may be,” pointed out Stanford School of Earth, Energy & Environmental Sciences researcher and study lead author Salvatore Pascale. “In the worst-case scenario, events like the ‘Day Zero’ drought may become about 100 times more likely than what they were in the early 20th century world.”

In a scenario in which greenhouse gas emissions remain high, ‘Day Zero’ scale droughts could afflict Cape Town and its surrounding region two or three times each decade. Under a scenario with intermediate-level emissions, there was still an increased risk of such multiyear droughts happening and also that they would last longer and be more severe than the 2015 to 2018 drought. This latest modelling reinforced previous research which had also indicated an increased likelihood of droughts in the region owing to carbon emissions.

“The information we can provide now with these new tools is much more precise,” he reported. “We can say with a higher degree of confidence that the role anthropogenic climate change has had so far has been quite large.”

The results of the research suggest the need for Cape Town to be able to aggressively manage its water supply. “[T]his is the moment to rethink the old way of managing water for a future when there will be less water available,” he advised. Further, the results of the research were also applicable to other parts of the world with climates similar to that of the Western Cape province, such as the US State of California, southern Europe, southern Australia and parts of South America.

“This study shows these events will be more likely in the future depending on how energetic we are in addressing the climate problem,” affirmed Pascale. “It can either be catastrophic or just a little bit better, but still worse than it is now – this is trying to give some indication about what the future might look like.”