The paleoclimate context and future trajectory of extreme summer hydroclimate in eastern Australia

Abstract

Eastern Australia recently experienced an intense drought (Millennium Drought, 2003–2009) and record‐breaking rainfall and flooding (austral summer 2010–2011). There is some limited evidence for a climate change contribution to these events, but such analyses are hampered by the paucity of information on long‐term natural variability. Analyzing a new reconstruction of summer (December–January–February) Palmer Drought Severity Index (the Australia‐New Zealand Drought Atlas; ANZDA, 1500–2012 Common Era), we find moisture deficits during the Millennium Drought fall within the range of the last 500 years of natural hydroclimate variability. This variability includes periods of multidecadal drought in the 1500s more persistent than any event in the historical record. However, the severity of the Millennium Drought, which was caused by autumn (March‐April‐May) precipitation declines, may be underestimated in the ANZDA because the reconstruction is biased toward summer and antecedent spring (September‐October‐November) precipitation. The pluvial in 2011, however, which was characterized by extreme summer rainfall faithfully captured by the ANZDA, is likely the wettest year in the reconstruction for Coastal Queensland. Climate projections (Representative Concentration Pathways (RCP) 8.5 scenario) suggest that eastern Australia will experience long‐term drying during the 21st century. While the contribution of anthropogenic forcing to recent extremes remains an open question, these projections indicate an amplified risk of multiyear drought anomalies matching or exceeding the intensity of the Millennium Drought.

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

“…In the much longer context of our rainfall reconstruction, 2010-2011 was one of the wettest warm seasons in the past several centuries, not only in Murray Basin but also in Monsoonal North, Rangelands, Southern Slopes and East Coast. Cook et al (2016) found similar results based on the ANZDA reconstruction of spatial variability in the PDSI. The 1979-1983 period of dry conditions in eastern Australia and the 1983 warm season and 1984 coolseason wet anomalies in the East Coast, Wet Tropics and Monsoonal North are also captured in the reconstructions.…”

Potential for tree rings to reveal spatial patterns of past drought variability across western Australia

“…Despite the high incidence of antiphase hydroclimatic conditions, we find at least one period of extreme drought during the 1830s was synchronous between inland (north and south) western and eastern Australia in the last two centuries (Cook et al 2016b, Gallant and Gergis 2011, Ho et al 2015 figures 3(a)-(c)). This finding suggests it is possible that drought conditions were widespread across the continent during this period; however, a more precise understanding of the spatial signature of this drought period (and other past drought and wet periods) is contingent upon the development of an Australia-wide drought atlas.…”

“…For example, two of the three major drought periods in inland western Australia (i.e. 1880s and 1950s) coincided with relatively wet periods in south-eastern Australia (figures 3(a)-(d); Cook et al 2016b. In fact, the 1950s drought in western Australia coincided with the highest decadal-scale stream flow of the Murray River (in south-eastern Australia) in the last 200 years (Gallant and Gergis 2011).…”

Investigating Relationships Between Australian Flooding and Large‐Scale Climate Indices and Possible Mechanism

“…As a dry and inhabited continent on Earth and with high streamflow variability, Australia is particularly prone to large-scale changes in hydroclimatic conditions (Cook et al, 2016;Verdon et al, 2004;Westra & Sharma, 2006;Zhang et al, 2016c). Meanwhile, flooding is one of the most severe natural disasters in Australia, with consequent impacts on many natural and social sectors (FitzGerald et al, 2010;Noji, 1995).…”