Abstract An understanding of tropical hydroclimate variability, the associated drivers and how it is likely to change is a major scientific and societal challenge that is acutely hampered by short instrumental records. We present a 246-year tree-ring drought reconstruction of the Standardised Precipitation Evaporation Index (SPEI) for monsoonal northern Australia for the end of the wet season (March–May; MAM). This reconstruction extends the instrumental record back by 150 years. Around one third of total annual rainfall falls during MAM, making it a crucial component of the monsoonal cycle. MAM is also the season most impacted by the differential decay process of Central Pacific (as opposed to Western Pacific) El Nino events that are linked with dry conditions over northern and northwestern Australia more generally. Our reconstruction therefore provides an opportunity to consider how central Pacific variability has modulated MAM hydroclimate in Australia's monsoonal north over the past two and a half centuries. We found that MAM hydroclimate extremes in the region have a strong, but asymmetric relationship with central Pacific sea surface temperatures (SSTs) and ENSO indices. Extremely wet MAMs in monsoonal north Australia were associated with cooler SSTs, above average rainfall across much of Australia, and often coincided with La Nina events. The spatial relationship between dry extremes and Pacific SSTs during dry events was generally, but weakly, consistent with the SST signature of central Pacific El Nino events. The association between reconstructed dry extremes in the monsoonal north and dry conditions across the rest of Australia is also less extensive and weaker than for wet events. Results suggest that more extreme wet events in the Australian monsoonal north likely reflect cool central Pacific SSTs and later termination of the Australian monsoon. Consecutive years with extremely dry MAMs became more frequent over the latter part of the 20th Century while the probability of an extreme dry MAM followed by an extreme wet MAM the next year peaked in the mid 20th Century and has since declined.

中文翻译：

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澳大利亚北部干旱重建中的极端水文气候与中太平洋海面温度不对称相关

摘要 了解热带水文气候变异性、相关驱动因素以及它如何可能发生变化是一项重大的科学和社会挑战，它受到短仪器记录的严重阻碍。我们展示了澳大利亚北部雨季结束时（3 月至 5 月；MAM）的标准化降水蒸发指数 (SPEI) 的 246 年树轮干旱重建。这次重建将乐器记录延长了 150 年。在 MAM 期间，年总降雨量的大约三分之一下降，使其成为季风周期的重要组成部分。MAM 也是受中太平洋（相对于西太平洋）厄尔尼诺事件的差异衰减过程影响最大的季节，这些事件与澳大利亚北部和西北部的干旱条件更普遍有关。因此，我们的重建提供了一个机会来考虑在过去两个半世纪中太平洋中部的变化如何调节澳大利亚季风北部的 MAM 水文气候。我们发现该地区的 MAM 极端水文气候与太平洋中部海面温度 (SST) 和 ENSO 指数有很强但不对称的关系。澳大利亚北部季风中极度潮湿的 MAM 与较冷的海温有关，澳大利亚大部分地区的降雨量高于平均水平，并且经常与拉尼娜事件同时发生。干旱事件期间极端干旱与太平洋海温之间的空间关系与中太平洋厄尔尼诺事件的海温特征总体上但较弱地一致。重建的北部季风极端干旱与澳大利亚其他地区的干旱条件之间的关联也没有潮湿事件那么广泛和弱。结果表明，澳大利亚季风北部更极端的潮湿事件可能反映了太平洋中部凉爽的海温和澳大利亚季风后来的终止。在 20 世纪后半叶，连续出现极端干燥 MAM 的年份变得更加频繁，而第二年发生极端干燥 MAM 和极端潮湿 MAM 的概率在 20 世纪中叶达到顶峰，此后开始下降。