Multi-century cool- and warm-season rainfall reconstructions for Australia's major climatic regions

Abstract

Abstract. 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

A review of past and projected changes in Australia's rainfall

“…Similarly, it was found that megadroughts exceeding 5‐years duration occurred in eastern Australia numerous times during the last millennium, including a 39‐year long drought during an unprecedented century of aridity (Vance et al, ). Similarly, the rate of recent declines in cool season rainfall in parts of southern Australia has been unusual though not unprecedented in the context of the last 400 years, while the spatial extent and duration of the Millennium Drought appears unprecedented over this multi‐century reconstruction period (Freund et al, ). These droughts challenge existing water storage strategies.…”

Debris flows in southeast Australia linked to drought, wildfire, and the El Niño–Southern Oscillation

“…The hydroclimatic conditions are also extraordinary in the longer term. Freund et al (2017), for instance, showed that the extent and severity of the Millennium Drought (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009) were unprecedented over the past 400 yr, and that the 2010-2011 period (Fig. 2B) was amongst the wettest summer periods in the past several centuries.…”

“…Drier areas (500-1000 mm yr -1 ), typically in rain shadows and at lower elevations, support dry open eucalyptus forests and woodlands, which have fire return intervals of 10-50 yr (Cheal, 2010). The timing of debris flows across the full study area was examined in relation to regional hydroclimate and wildfire data between 2003 and 2013, when climate fluctuations were large (van Dijk et al, 2013;Freund et al, 2017).…”

“…In southeast Australia, the series of climatic events at the start of the 21 st century produced both exceptionally dry and wet conditions (Freund et al, 2017). During this period, debris flows occurred regularly in forested and relatively stable postorogenic mountain ranges, with incidents of both runoff-generated debris flows from short and intense rainfall on burned areas, and landslide-generated debris flows from extended periods of heavy rainfall and saturated conditions (both types described in Meyer et al, 2001).…”

Digitization of weekly Murrumbidgee River heights at Hay South Eastern Australia 1873–2017

“…It is important to consider finer scale or local hydroclimatic patterns in relation to large-scale climate drivers of a region so that more spatially focussed regional assessments of drought and flood variability and hence water availability can be made (Freund et al, 2017). This also applies when considering the effect of catchment development along a river (Kingsford and Thomas, 2001).…”