Understanding the anthropogenic nature of the observed rainfall decline across South Eastern Australia

  • Timbal B
  • Arblaster J
  • Braganza K
 et al. 
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The South Eastern Australian Climate Initiative (SEACI) began in 2006 and initially was
planned as a three-year, $7.5 million research program aimed at investigating the causes and
impacts of climate change and climate variability across south eastern Australia (SEA),
including the Murray-Darling Basin (MDB). This region is one of the country?s most valuable
primary production areas. The MDB alone produces more than one-third of Australia?s food
supply and generates 40 per cent of the nation?s agricultural income, with 70 per cent of
Australian irrigation occurring in this region.
Phase 1 of the program (SEACI-1) started in January 2006 and ran to the end of 2008; it was
further extended from January 2009 to June 2009 (SEACI-1P). SEACI-1 had three major
research themes: better understanding of current climate and its drivers (Theme 1), improved
long-term projections of climate change and its impacts on water resources (Theme 2), and
improved seasonal forecasting (Theme 3). More details on the program can be found on the
SEACI web site: http://www.seaci.org/.
The focus in Theme 1 was on the characterisation and attribution of current climate: including
the assessment of the current state of knowledge about climate variability and its drivers over
SEA. It was organised around a large number of projects carried out by the two research partners - the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Bureau of Meteorology (BoM). Researchers from the CSIRO Marine and Atmospheric Research (CMAR) Division and the BoM participated in SEACI under the umbrella of the Centre for Australian Weather and Climate Research (CAWCR). Projects in Theme 1 involved:| the review of previous studies of climate variability in the region;| the analysis of site-specific meteorological records and the re-analysis data set with a view
to detecting and quantifying any trends or shifts in climate;| experimenting with global climate models to provide insight into the extent to which recent
climatic trends and shifts can be attributed to various causal factors, including the enhanced
greenhouse effect; and| the development and validation of downscaling methodologies in order to provide local
climate information in conjunction with research in Theme 2 (long-term projections) and
Theme 3 (seasonal predictions).
The projects in Theme 1 were organised (Fig. 1) to maximise both the synergy within the Theme and the flow of information into the other two themes (future projections and seasonal predictions).
Figure 1 outlines the progress made during the course of the program starting from the basic
undertaking in Project 1.1.1 but also the organisation of the research into different spatial scales:| broad-scale - with a view to understanding the large-scale modes of variability which influence regional climate and how theses features are evolving with time;| regional scale ? at a scale of the SEA region of interest; and| local scale - with a view to considering impacts at a scale relevant to climate impact studies.
Specific details of all the themes and the various projects are available on the SEACI web site.
In this report, the contribution from the BoM across SEACI-1 and SEACI-1P is summarised.
Fig. 2 shows the logic of the work performed, the interactions between the various projects
(reported here as chapters), its relevance to the overall Theme 1 research plan and the extension
of the work during SEACI-1P.
The changes affecting SEA are described in Chapter 2. The contribution of several large-scale modes of variability to the ongoing changes in SEA climate is evaluated in Chapter 3. In chapters 4 to 6, we try to better understand the cause of the observed changes by using simulation of the 20th century climate with different external forcings. These chapters also describe the development (Chapter 4), evaluation (Chapter 5) and application (Chapter 6) the BoM statistical downscaling model (SDM). The BoM SDM allows us to enhance the signal to noise ratio, which is recognised as the biggest challenge when it comes to attributing changes at regional scales for highly variable rainfall (see p714 in Solomon et al. 2007). The following three chapters describe additional studies which were carried out during SEACI-1P:| the evaluation of the relationship between global warming (GW) and the sub-tropical ridge (STR) in climate model simulations of the 20th century (Chapter 7);| a comparison of the ongoing drought with the previous worst drought in the instrumental
record before and during World War II, and a synthesis of the role of tropical modes of variability in both droughts (Chapter 8); and| an analysis of the influence of the STR on the hydrological cycle diagnosed using the newly
formed high resolution AWAP dataset (Chapter 9).
Chapter 10 has been included to update some earlier findings to the end of 2009 using the latest
BoM dataset (i.e. AWAP). This chapter also includes additional information not reported earlier
during SEACI-1 but presented at various SEACI meetings and that contributes to answer the original key scientific questions that were asked at the start of the SEACI-1 (see box below).
The major findings are summarised against the key questions and a brief discussion of the outstanding scientific questions are discussed in Chapter 11, thus introducing the research
proposed as part of the SEACI-2 science plan.

Author-supplied keywords

  • a partnership between csiro
  • and climate research
  • and the bureau of
  • centre for australian weather
  • decline across
  • meteorology
  • of the observed rainfall
  • understanding the anthropogenic nature

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  • B. Timbal

  • J. Arblaster

  • K. Braganza

  • E. Fernandez

  • H. Hendon

  • B. Murphy

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