In 2017-2019 southeast Australia experienced one of its most severe droughts since 1900. Rainfall over the region encompassing the Murray-Darling Basin was consistently below average for three consecutive cool seasons, an unprecedented event on record. A strong positive Indian Ocean Dipole event has been previously suggested to have intensified the conditions of the drought in 2019, however the state of the climate drivers cannot fully explain the onset and development of this drought. In this study, we adopt a different approach to investigate processes other than remote climate drivers that may have triggered the drought. Using a Lagrangian model to identify moisture sources to the Murray Darling Basin, we show that local processes were crucial in explaining the onset and development of the drought. We identify the oceanic and terrestrial sources of atmospheric moisture over the Murray Darling Basin and show for the first time a significant decline in rainfall moisture supply from the Tasman Sea in 2017 and 2018. We further show that anomalous atmospheric circulation transported the expected moisture northward toward the Maritime Continent. Our results provide an explanation for the moisture and rainfall deficit that caused the 2017-19 southeast Australian drought. Understanding the processes that led to the 2017-2019 drought is an important step towards improved predictions and planning for future multi-year droughts in Australia.

中文翻译：

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水分来源的变化导致了2017-2019年澳大利亚东南部干旱的发生和发展


2017-2019 年，澳大利亚东南部经历了 1900 年以来最严重的干旱之一。墨累-达令盆地地区的降雨量连续三个凉爽季节低于平均水平，这是有记录以来前所未有的事件。此前曾有人认为，强烈的印度洋偶极子事件加剧了 2019 年的干旱状况，但气候驱动因素的状态无法完全解释此次干旱的发生和发展。在这项研究中，我们采用了不同的方法来调查可能引发干旱的远程气候驱动因素以外的过程。使用拉格朗日模型来确定墨累达令盆地的水分来源，我们表明局部过程对于解释干旱的发生和发展至关重要。我们确定了墨累达令盆地大气水分的海洋和陆地来源，并首次显示 2017 年和 2018 年塔斯曼海的降雨水分供应显着下降。我们进一步表明，异常的大气环流将预期的水分向北输送到海洋大陆。我们的研究结果为导致 2017-19 年澳大利亚东南部干旱的水分和降雨量不足提供了解释。了解导致 2017-2019 年干旱的过程是改进澳大利亚未来多年干旱预测和规划的重要一步。