Megadroughts and pluvials in southwest Australia: 1350–2017 CE

Abstract

Declining winter rainfall coupled with recent prolonged drought poses significant risks to water resources and agriculture across southern Australia. While rainfall declines over recent decades are largely consistent with modelled climate change scenarios, particularly for southwest Australia, the significance of these declines is yet to be assessed within the context of long-term hydroclimatic variability. Here, we present a new 668-year (1350–2017 CE) tree-ring reconstruction of autumn–winter rainfall over inland southwest Australia. This record reveals that a recent decline in rainfall over inland southwest Australia (since 2000 CE) is not unusual in terms of either magnitude or duration relative to rainfall variability over the last seven centuries. Drought periods of greater magnitude and duration than those in the instrumental record occurred prior to 1900 CE, including two ‘megadroughts’ of > 30 years duration in the eighteenth and nineteenth centuries. By contrast, the wettest > decadal periods of the last seven centuries occurred after 1900 CE, making the twentieth century the wettest of the last seven centuries. We conclude that the instrumental rainfall record (since ~ 1900 CE) does not capture the full scale of natural hydroclimatic variability for inland southwest Australia and that the risk of prolonged droughts in the region is likely much higher than currently estimated.

Megadroughts in the Common Era and the Anthropocene

“…Ice core records suggest that south western Australia was especially drought prone in the mid 1300s 128 and during the eighteenth and nineteenth centuries. Tree ring records corroborate some of these events, indicating major multi decadal megadroughts in 1755-1785 CE, 1828-1859 CE, and 1889-1908 CE 15 . The coincidence of the tree ring derived 1828-1859 CE megadrought in western Australia with coral derived evidence of low streamflow in Queensland (the lowest in the region since the 1600s 38 ) suggests this event might have been especially widespread 15 .…”

“…These include the 'Strange Parallels' drought from 1756-1768 CE that affected peninsular India, Southeast Asia, and central Russia 43 and the Great Victorian drought from 1876-1878 CE that affected India, Southeast Asia, and China 43,125,126 128 , and corals along the east coast of Australia 38 . More recently, however, advances have been made to develop local proxy records, including new tree ring reconstructions in Western Australia that extend back over 600 years 15 .…”

Getting to the Root of Organic Inputs in Groundwaters: Stygofaunal Plant Consumption in a Calcrete Aquifer

“…This study using gut analyses combined with isotopic modelling confirms that tree roots are both habitat and source of OM for stygofauna, as has been previously suggested in several groundwater ecosystems in inland Western (Jasinska et al, 1996) and Eastern continental Australia (Hancock and Boulton, 2008), as well as Tasmania (Jasinska and Knott, 2000). The native cypress Callitris, a shallow-rooted but very long-lived tree (Cullen and Grierson, 2009;O'Donnell et al, 2021) was detected in amphipods AM2 (LR) and copepods C (HR). Recent investigations of the Sturt Meadows stygofaunal community suggested a substantial shift in the OM incorporated by amphipods (AM1 and AM2) from root-based during LR to a POC-based diet under HR (Saccò et al, 2021a).…”

“…Occasional eucalypts and Melaleuca (Myrtaceae) are found in creek zones (Hamano et al, 2011). The calcrete formation at Sturt Meadows sits upstream of a salt lake, Lake Raeside, which like many lakes within the region is surrounded by stands of Callitris columellaris (e.g., O'Donnell et al, 2021).…”

Ring-width and blue-light chronologies of Podocarpus lawrencei from southeastern mainland Australia reveal a regional climate signal

“…Mt Read, Tasmania; Cook et al, 2000). Long-term reconstructions for mainland Australia that are based on in situ, annually resolved records (rather than remote proxies) are very limited (O'Donnell et al, 2021;Cullen and Grierson, 2008;Allen et al, 2020; notably these are all hydroclimate reconstructions). Given the strong influence of temperature as a limiting growth factor in higher-elevation areas, the Australian Alps and Victoria's central highlands are prime contenders to further validate the regional nature of these signatures back in time.…”