Increasing risk of another Cape Town “Day Zero” drought in the 21st century

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 47; pp. 29495 - 29503
• Main Authors: Pascale, Salvatore, Kapnick, Sarah B., Delworth, Thomas L., Cooke, William F.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 24.11.2020
• Subjects: Adequacy; Anthropogenic factors; Climate Change; Climate models; Drought; Droughts; Ecological Parameter Monitoring - statistics & numerical data; Emission; Environmental risk; Forecasting; Global warming; Models, Theoretical; Physical Sciences; Probability; Rain; Rainfall; Seasons; South Africa; South Africa; climate-change detection; event attribution; drought; climate extremes; large ensemble simulations
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2009144117

Three consecutive dry winters (2015–2017) in southwestern South Africa (SSA) resulted in the Cape Town “Day Zero” drought in early 2018. The contribution of anthropogenic global warming to this prolonged rainfall deficit has previously been evaluated through observations and climate models. However, model adequacy and insufficient horizontal resolution make it difficult to precisely quantify the changing likelihood of extreme droughts, given the small regional scale. Here, we use a high-resolution large ensemble to estimate the contribution of anthropogenic climate change to the probability of occurrence of multiyear SSA rainfall deficits in past and future decades. We find that anthropogenic climate change increased the likelihood of the 2015–2017 rainfall deficit by a factor of five to six. The probability of such an event will increase from 0.7 to 25% by the year 2100 under an intermediate-emission scenario (Shared Socioeconomic Pathway 2-4.5 [SSP2-4.5]) and to 80% under a high-emission scenario (SSP5-8.5). These results highlight the strong sensitivity of the drought risk in SSA to future anthropogenic emissions.