Abstract
Abstract. Southeast Australia (SEA) experienced a protracted drought during the mid-1990s until early 2010 (known as the Big Dry or Millennium Drought) that resulted in serious environmental, social and economic effects. This paper analyses a range of historical climate data sets to place the recent drought into context in terms of Southern Hemisphere inter-annual to multi-decadal hydroclimatic variability. The findings indicate that the recent Big Dry in SEA is in fact linked to the widespread Southern Hemisphere climate shift towards drier conditions that began in the mid-1970s. However, it is shown that this link is masked because the large-scale climate drivers responsible for drying in other regions of the mid-latitudes since the mid-1970s did not have the same effect on SEA during the mid- to late 1980s and early 1990s. More specifically, smaller-scale synoptic processes resulted in elevated autumn and winter rainfall (a crucial period for SEA hydrology) during the mid- to late 1980s and early 1990s, which punctuated the longer-term drying. From the mid-1990s to 2010 the frequency of the synoptic processes associated with elevated autumn/winter rainfall decreased, resulting in a return to drier than average conditions and the onset of the Big Dry. The findings presented in this paper have marked implications for water management and climate attribution studies in SEA, in particular for understanding and dealing with "baseline" (i.e. current) hydroclimatic risks.
Highlights
1.1 The Big Dry and other protracted droughts in Australia’s historyAustralia, with its naturally highly variable climate, is no stranger to drought conditions
This paper aims to establish if the Big Dry that impacted Southeast Australia (SEA) from the mid-1990s to 2010 is related to the 1970s climate shift experienced in many regions of the Southern Hemisphere (Sect. 3), and in particular the step change in climate observed in southwest Western Australia (SWWA)
What would have happened to water resources and supplies in the region in the absence of these wet winters and autumns? Given the experience of SWWA and the findings presented here, it is suggested that this should be considered as a possible “scenario” in terms of water management planning, and water corporations in Victoria are using an immediate return to the dry conditions of the Big Dry as a possible future scenario alongside climate change projections (DSE, 2011)
Summary
1.1 The Big Dry and other protracted droughts in Australia’s historyAustralia, with its naturally highly variable climate, is no stranger to drought conditions. From 1937 to 1945 Southeast Australia (SEA) was subjected to another multiyear drought, known as the World War II Drought, while more recently the Big Dry (or Millennium Drought) affected SEA during the mid-1990s through to early 2010 and resulted in a marked reduction in rainfall and runoff (NWC, 2006; Murphy and Timbal, 2008; Verdon-Kidd and Kiem, 2009a, b; Kiem and Verdon-Kidd, 2010; Gallant et al, 2012). In terms of annual rainfall deficits the Big Dry has been shown to be more severe in parts of SEA than the earlier multi-year droughts for durations of 3–19 years (CSIRO, 2012); the Federation and World War II droughts were more widespread (Verdon-Kidd and Kiem, 2009a). The Big Dry was characterised by a lack of high 1day rainfall totals (Murphy and Timbal, 2008; Verdon-Kidd and Kiem, 2009a) and wet months (CSIRO, 2012), which is consistent with a reduction in the amount of rainfall
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