Department of Earth System Science, Stanford University, Stanford, CA 94305;
Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, NJ 08540.
Proc Natl Acad Sci U S A. 2020 Nov 24;117(47):29495-29503. doi: 10.1073/pnas.2009144117. Epub 2020 Nov 9.
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.
连续三个干旱的冬季（2015-2017 年）导致 2018 年初南非西南部开普敦出现了“水荒零日”。人为引起的全球变暖对这一长期降雨短缺的影响此前已经通过观测和气候模型进行了评估。然而，由于区域规模较小，模型的充分性和不足的水平分辨率使得很难精确量化极端干旱发生可能性的变化。在这里，我们使用高分辨率的大型集合来估计人为气候变化对过去和未来几十年南非南部地区多年降雨短缺发生概率的贡献。我们发现，人为气候变化将 2015-2017 年降雨短缺的可能性增加了五到六倍。在中等排放情景（共享社会经济途径 2-4.5 [SSP2-4.5]）下，到 2100 年，这种事件的概率将从 0.7%增加到 25%，在高排放情景（SSP5-8.5）下，这种事件的概率将增加到 80%。这些结果突出表明，南非南部干旱风险对未来人为排放的敏感性很强。
