Australia's Murray-Darling Basin experienced three consecutive years of meteorological drought across 2017–2019, collectively named the ‘Tinderbox Drought’. Rainfall deficits during the three-year drought were most pronounced in the Australian cool season (April to September). Deficits in both the cool season and annual total rainfall were unprecedented in the instrumental record. However, the instrumental record provides just one of a range of equally plausible climate trajectories that could have occurred during this period. To determine if the Tinderbox Drought was outside this range, we used observational data from prior to the onset of the drought to construct Linear Inverse Models (LIMs) that emulate the stationary statistics of Australian rainfall and its connection to global sea surface temperature (SST) anomalies. Overall, we find that rainfall deficits were most unusual in the northern Murray-Darling Basin, and during the final year of the drought. The global SST anomalies observed during the first two years of the Tinderbox Drought, particularly the cool anomalies in the central tropical Pacific and western Indian Ocean, are not typically associated with low rainfall across the Murray-Darling Basin. In terms of single-year rainfall anomalies, the only aspect of the Tinderbox Drought that was beyond the range of the LIMs was annual-total rainfall over the northern Murray-Darling Basin during 2019. This coincided with an extreme positive Indian Ocean Dipole event that was also beyond the range of the LIMs. When considered in terms of basin-wide rainfall over the full three years, rainfall deficits during the Tinderbox Drought were beyond the LIM range in terms of both cool-season and annual-total rainfall. This suggests an anthropogenic contribution to the severity of the drought—likely exacerbated by the 2019 extreme positive Indian Ocean Dipole event.

中文翻译：

---

澳大利亚 2017-2019 年的 Tinderbox 干旱有多不寻常？


澳大利亚的墨累-达令盆地在 2017 年至 2019 年期间经历了连续三年的气象干旱，统称为“火药箱干旱”。三年干旱期间的降雨不足在澳大利亚凉爽季节（4 月至 9 月）最为明显。凉爽季节和年总降雨量的赤字在仪器记录中都是前所未有的。然而，仪器记录仅提供了这一时期可能发生的一系列同样合理的气候轨迹之一。为了确定 Tinderbox 干旱是否超出此范围，我们使用干旱开始前的观测数据构建了线性逆模型 （LIM），该模型模拟澳大利亚降雨的稳态统计数据及其与全球海面温度 （SST） 异常的联系。总体而言，我们发现，在墨累-达令盆地北部和干旱的最后一年，降雨不足最为罕见。在 Tinderbox 干旱的头两年观察到的全球 SST 异常，尤其是热带太平洋中部和西印度洋的凉爽异常，通常与墨累-达令盆地的低降雨量无关。就单年降雨异常而言，Tinderbox 干旱唯一超出 LIM 范围的方面是 2019 年墨累-达令盆地北部的年总降雨量。这与一个极端的正印度洋偶极子事件相吻合，该事件也超出了 LIM 的范围。如果从整整三年的流域降雨量来看，Tinderbox 干旱期间的降雨赤字在冷季和年总降雨量方面都超出了 LIM 的范围。 这表明人为因素导致了干旱的严重性，而 2019 年的印度洋偶极子事件可能加剧了这一情况。