Rainfall variations in south-eastern Australia part 1: consolidating evidence from pre-instrumental documentary sources, 1788-1860

This study fills an important gap in south-eastern Australia's climate record by compiling qualitative historical data from the time of first European settlement of Australia in 1788 until widespread meteorological observations become available in 1860. In this study, we consolidate twelve documentary-based rainfall chronologies for five sub-regions of south-eastern Australia (SEA) over the 1788-1860 period using a range of secondary historical sources. Our analysis identified 27 drought years in SEA between 1788 and 1860, and 14years of high rainfall in New South Wales (NSW) between 1788 and 1840. Given that our current understanding of Australian drought is still largely confined to the post-1900 period covered by instrumental records, we provide an outline of the drought and wet periods to provide a consolidated reference of historical accounts of lesser known pre-instrumental rainfall variations for researchers working in the field. This index is also intended to serve as an independent inter-annual verification source for palaeoclimate reconstructions being developed in the Australian region. This study confirms that SEA has experienced considerable rainfall variability that has influenced past Australian societies since the first European settlement in 1788. Of the droughts identified in this study, 1837-1841 was the longest and most widespread event influencing all subregions. The 1793-1809 period was particularly wet, with periods of heavy rainfall often resulting in devastating floods on the Hawkesbury River region of Sydney. Despite the geographical biases present in the documentary material, it is clear that historical records provide important information on rainfall variations in SEA and their societal impacts over the 1788-1860 pre-instrumental period. The results presented here provide an important basis for developing an extended rainfall index for eastern NSW from 1788-2008, and is the subject of part 2 of this study (Gergis J, Ashcroft L. 2012. Rainfall variations in south-eastern Australia part 2: a comparison of documentary, early instrumental and palaeoclimate records, 1788-2008. International Journal of Climatology).