Increasing risk of another Cape Town’s Day Zero drought in 21st century
Three consecutive dry winters (2015–2017) in southwestern South Africa (SSA) resulted in the Cape Town “Day Zero” drought in early 2018. Combined with management practices and infrastructure shortcomings, the drought caused one of the most serious water crises ever experienced in any heavily populated metropolitan area, with extensive economic impacts. The authors of this study applied a high-resolution (0.5◦×0.5◦) large ensemble, generated from the newly developed Seamless System for Prediction and EArth System Research (SPEAR) global climate model developed at GFDL, to investigate regional hydroclimatic risk.
The contribution of anthropogenic global warming to this prolonged rainfall deficit has previously been evaluated through climate models. However, model adequacy and insufficient horizontal resolution make it difficult to quantify the changing likelihood of extreme droughts given the small regional scale. By using a high-resolution global climate model, the authors were able to provide a comprehensive perspective on the changing decadal risk of extreme droughts in SSA. Their findings indicate that anthropogenic climate change made the drought five-to-six times more likely than it would have been in the 19th century. By the end of the 21st century, the probability of the occurrence of a ‘Day Zero’ drought may drastically increase, implying that such catastrophic droughts may happen almost every year. Additionally, through analysis of the atmospheric circulation response, the authors identified a reduction in precipitation during the shoulder seasons (April, May and September)—as in 2015–17—as the likely cause of drought risk in SSA in the 21st century.
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More from Climate.gov: Cape Town Drought