Rainfall variations in south‐eastern Australia part 2: a comparison of documentary, early instrumental and palaeoclimate records, 1788–2008

Abstract

ABSTRACT:In part 1 of this study, Fenby and Gergis (Fenby C, Gergis J. 2012. A rainfall history of south-eastern Australia Part 1: comparing evidence from documentary and palaeoclimate records, 1788-1860. International Journal of Climatology) established a documentary chronology of droughts and wet years in south-eastern Australia (SEA) from first European settlement in 1788 until widespread meteorological observations begin in 1860. We now compare this newly developed documentary record to a five-station network of historical instrumental rainfall observations from the Sydney region for 1832-1859, and a 45-station rainfall network from a broader range of SEA locations over the 1860-2008 period. After assessing geographical biases in the documentary and instrumental record due to population settlement, we identify eastern New South Wales (NSW) as the subregion of SEA that is capable of providing a continuous record of wet and dry years back to 1788. Documentary, historical instrumental and modern rainfall observations are then combined to develop an eastern NSW drought and wet year index over the 1788-2008 period. The eastern NSW drought and wet year index is compared to palaeoclimate reconstructions of SEA rainfall and El Niño-Southern Oscillation (ENSO) since 1788. We investigate the relationship between droughts and wet years in eastern NSW and ENSO back to 1788, noting that the coastal NSW rainfall-ENSO relationship is not as pronounced as in inland areas of eastern Australia. While it is clear that ENSO influences rainfall variability in the broader SEA region, the signal recorded in coastal NSW is weak. This is most likely reflecting local orographic rainfall effects and deficiencies in the wet phase of the documentary record. Nonetheless, this study is the first of its kind in the Australasian region to combine documentary, early instrumental and modern meteorological rainfall observations using internationally comparable techniques, a significant advance in historical climatology for the region. The results of this study provide an opportunity for Australia to be included in cross-regional drought comparisons from the Indo-Pacific regions of the Southern Hemisphere.Additional Supporting information may be found in the online version of this article.

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

“…Discrepancies between our reconstruction and documentary sources might also arise from the use of annual means, which might dilute a seasonal signal. Comparing annual means of our seasonal reconstructions (not shown) extreme years such as 1860 (East Coast) stand out and mostly agree with the wet and dry classified years found by Gergis and Ashcroft (2012) for southeast Australia.…”

Floods and climate: emerging perspectives for flood risk assessment and management

“…Bronnimann, 2007), there is still no clear understanding of how and under which circumstances the SST signal transmitted from the tropics to Europe can lead to precipitation extremes associated with flooding. Although other parts of the world were also affected by above-average precipitation in the late 19th century (Gergis and Ashcroft, 2012), the reasons why this period was so exceptional in Europe are still unclear.…”

Long-term stationarity of El Niño–Southern Oscillation teleconnections in southeastern Australia

“…The historical instrumental data may provide verification of the palaeoclimate analysis of Gergis et al (2012), broaden the analysis of long-term eastern SEA rainfall variability conducted by Gergis and Ashcroft (2013), and shed more light on the behaviour of ENSO during the 1800s.…”

“…Cooler global temperatures due to volcanic eruptions or other external climate forcings have additionally been linked to the suppression of ENSO teleconnections (Reason et al 1998;Mann et al 2000), while some statistical analyses of global ENSO-rainfall correlations suggest that there may be no physical basis behind changes in teleconnection strength, and that low-frequency fluctuations are essentially random (van Oldenborgh and Burgers 2005;Wittenberg 2009). In recent years, newly recovered instrumental data have allowed for the extension of homogenised monthly rainfall observations for SEA back to 1860 (Timbal and Fawcett 2012;Gergis and Ashcroft 2013;Ashcroft et al 2014b). Further historical data recovery by Ashcroft et al (2014a) provides additional instrumental data for regions of SEA as far back as European settlement in 1788.…”