NOAA/WDS Paleoclimatology - Allen - Mesa - ATSE - ITRDB AUSL047

Australian seasonal rainfall is strongly affected by large-scale ocean-atmosphere climate influences. In this study, we exploit the links between these precipitation influences, regional rainfall variations, and palaeoclimate proxies in the region to reconstruct Australian regional rainfall between four and eight centuries into the past. We use an extensive network of palaeoclimate records from the Southern Hemisphere to reconstruct cool (April-September) and warm (October-March) season rainfall in eight natural resource management (NRM) regions spanning the Australian continent. Our bi-seasonal rainfall reconstruction aligns well with independent early documentary sources and existing reconstructions. Critically, this reconstruction allows us, for the first time, to place recent observations at a bi-seasonal temporal resolution into a pre-instrumental context, across the entire continent of Australia. We find that recent 30- and 50-year trends towards wetter conditions in tropical northern Australia are highly unusual in the multi-century context of our reconstruction. Recent cool-season drying trends in parts of southern Australia are very unusual, although not unprecedented, across the multi-century context. We also use our reconstruction to investigate the spatial and temporal extent of historical drought events. Our reconstruction reveals that the spatial extent and duration of the Millennium Drought (1997-2009) appears either very much below average or unprecedented in southern Australia over at least the last 400 years. Our reconstruction identifies a number of severe droughts over the past several centuries that vary widely in their spatial footprint, highlighting the high degree of diversity in historical droughts across the Australian continent. We document distinct characteristics of major droughts in terms of their spatial extent, duration, intensity, and seasonality. Compared to the three largest droughts in the instrumental period (Federation Drought, 1895-1903; World War II Drought, 1939-1945; and the Millennium Drought, 1997-2005), we find that the historically documented Settlement Drought (1790-1793), Sturt's Drought (1809-1830) and the Goyder Line Drought (1861-1866) actually had more regionalised patterns and reduced spatial extents. This seasonal rainfall reconstruction provides a new opportunity to understand Australian rainfall variability by contextualising severe droughts and recent trends in Australia.

澳大利亚季节性降水深受大尺度海-气气候系统的影响。本研究依托该区域降水影响因子、区域降水变化与古气候代用指标（palaeoclimate proxies）之间的关联，重建了过去4至8个世纪的澳大利亚区域降水序列。我们借助南半球广泛分布的古气候记录网络，对覆盖澳大利亚全大陆的8个自然资源管理（natural resource management, NRM）区域的冷季（4-9月）与暖季（10-3月）降水开展重建。本次双季降水重建结果与独立早期文献记录及已有重建成果吻合度良好。尤为关键的是，本次重建首次实现了将澳大利亚全大陆范围内、具备双季时间分辨率的现代观测序列，置于器测时代前的气候背景之中。研究发现，澳大利亚热带北部地区近30年与50年的湿化趋势，在本次重建的多世纪尺度背景下极为罕见。澳大利亚南部部分区域近期出现的冷季干旱化趋势，同样在多世纪尺度下显得反常，尽管并非史无前例。我们还借助本次重建探究了历史干旱事件的时空分布特征。结果显示，千年大干旱（Millennium Drought，1997-2009）的空间影响范围与持续时长，至少在过去400年的澳大利亚南部地区来看，要么远低于平均水平，要么可谓前所未有。本次重建识别出过去数百年间多场严重干旱事件，这些干旱的空间影响范围差异显著，凸显了澳大利亚大陆历史干旱事件的高度多样性。我们还梳理了重大干旱事件在空间范围、持续时长、强度与季节特征上的鲜明特征。相较于器测时代的三场特大干旱（1895-1903年联邦干旱、1939-1945年二战干旱及1997-2005年千年大干旱），历史文献记载的定居者干旱（1790-1793年）、斯特特干旱（1809-1830年）与戈伊德线干旱（1861-1866年），实际呈现出更强的区域化特征与更小的空间影响范围。本次季节性降水重建为我们通过将严重干旱与近期趋势置于历史背景下，理解澳大利亚降水变异性提供了全新契机。