Links between the Big Dry in Australia and hemispheric multi-decadal climate variability – implications for water resource management

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.

Synchronicity of historical dry spells in the Southern Hemisphere

“…Rather, based on the results presented here, it appears that overall the period 1910 through to 1950 was dry for regions south of 30 • (particularly the mid-1920s to mid-1940s), followed by a relatively wet period (i.e., absence of prolonged dry periods) from 1950 through to 1980 and a return to dry thereafter (based on the 5 and 10 rainfall rankings). This is consistent with studies that suggest cyclic activity in wet and dry periods in the historical records (e.g., Erskine and Warner, 1988;Verdon-Kidd and Kiem, 2009;Hastenrath and Polzin, 2011). Research presented in CSIRO (2012) suggests that drought periods are more likely during periods of accelerated global warming (and increasing intensity of the subtropical ridge), rather than during periods when the rate of global warming is lower.…”

“…5, it appears that the east coast of South America, the east coast of South Africa, southwest and southeast of Australia and southern New Zealand all experienced a dry spell during the 8-year "Federation Drought" period (∼ 1895-1902). This result suggests a reduction in easterly flow south of 30 • during this time, a condition often associated with El Niño conditions (note that the Federation Drought was primarily driven by an extended El Niño phase (Verdon-Kidd and Kiem, 2009)). While the exact spatial extent of this dry spell is not clear (due to the reduced number of stations recording rainfall during this time) the results imply a degree of temporal consistency during this time for many regions of the Southern Hemisphere.…”

“…Following this, a severe drought gripped northern and eastern Australia, which lasted from ∼ 1895-1902 as shown in Fig. 4 (Verdon-Kidd and Kiem, 2009). The Federation Drought, as it became known, was the most severe (in terms of rainfall deficits) of Australia's three iconic protracted droughts, including the Big Dry (∼ 1997-2010) and the World War II Drought (∼ 1937-1945) (Verdon-Kidd and Kiem, 2009).…”

“…4 (Verdon-Kidd and Kiem, 2009). The Federation Drought, as it became known, was the most severe (in terms of rainfall deficits) of Australia's three iconic protracted droughts, including the Big Dry (∼ 1997-2010) and the World War II Drought (∼ 1937-1945) (Verdon-Kidd and Kiem, 2009). Station data with records dating back to 1890 were analyzed to determine if the Federation Drought was confined to Australia, or if this dry spell was also synchronous across parts of the Southern Hemisphere (Fig.…”

A Synoptic Classification of Inflow-Generating Precipitation in the Snowy Mountains, Australia

“…High precipitation variability also exists on intra-annual time scales. Precipitation in winter and spring is heavily influenced by the prevailing midlatitude westerly winds in conjunction with orographic enhancement, and these are commonly considered to be the wettest seasons (Snowy Hydro Limited 2003;Pook et al 2006;Cai and Cowan 2008;Ummenhofer et al 2009;Chubb et al 2011). Highintensity and warm spring rains falling onto the snowpack are a major source of inflows (McGowan et al 2009), generating as much as 50% of the total annual inflows to the hydroelectric catchments (Snowy Hydro Limited 2003).…”