Regional rainfall decline in Australia attributed to anthropogenic greenhouse gases and ozone levels

Journal name:
Nature Geoscience
Volume:
7,
Pages:
583–587
Year published:
DOI:
doi:10.1038/ngeo2201
Received
Accepted
Published online
Corrected online

Precipitation in austral autumn and winter has declined over parts of southern and especially southwestern Australia in the past few decades1, 2, 3, 4. According to observations and climate models, at least part of this decline is associated with changes in large-scale atmospheric circulation1, 2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, including a poleward movement of the westerly winds and increasing atmospheric surface pressure over parts of southern Australia. Here we use a high-resolution global climate model to analyse the causes of this rainfall decline. In our simulations, many aspects of the observed regional rainfall decline over southern and southwest Australia are reproduced in response to anthropogenic changes in levels of greenhouse gases and ozone in the atmosphere, whereas anthropogenic aerosols do not contribute to the simulated precipitation decline. Simulations of future climate with this model suggest amplified winter drying over most parts of southern Australia in the coming decades in response to a high-end scenario of changes in radiative forcing. The drying is most pronounced over southwest Australia, with total reductions in austral autumn and winter precipitation of approximately 40% by the late twenty-first century.

At a glance

Figures

  1. Time-mean precipitation averaged over the March-August season for 1961-1990.
    Figure 1: Time-mean precipitation averaged over the March–August season for 1961–1990.

    Units are millimetres per month. See ‘Data sources section in Methods for further information on observational data. a, Observations from BoM/AWAP. b, Observations from CRU of the University of East Anglia, UK. c, Model-simulated precipitation; shown here is a five-member ensemble mean from ALLFORC experiments (see Table 1 for description of ensemble).

  2. Precipitation differences for the March-August period between two time periods.
    Figure 2: Precipitation differences for the March–August period between two time periods.

    Units are millimetres per month. Stippling indicates regions that did not pass a statistical significance test (see Methods for details on testing and observational data sources). a, Precipitation differences calculated as the 1981–2010 mean minus the 1911–1970 mean using the BoM/AWAP observations. b, Precipitation differences calculated as the 1981–2012 mean minus the 1911–1970 mean using the CRU observations. c, The same as in b using the ensemble mean of the ALLFORC experiments. d, The same as in b for ANTHRO. e, The same as in b for NATURAL. f, Precipitation differences calculated as the 2021–2060 mean minus the 1911–1970 mean using the ensemble mean of the ALLFORC experiments.

  3. Assessing the likelihood of rainfall decline and contributing physical factors.
    Figure 3: Assessing the likelihood of rainfall decline and contributing physical factors.

    a, Colour-shaded regions indicate distribution of differences between 32-year means and 60-year means of March–August precipitation, spatially averaged over the continental regions of southwest Australia (110° E–120° E, 39° S–30° S). The distribution is derived by resampling a long CONTROL simulation as discussed in the text. The values along the y axis (indicating frequency of occurrence) are normalized so that the sum of all the vertical bars equals one. The position of the filled circles along the x axis denotes precipitation differences for 1981–2012 minus 1911–1970 for various experiments (the position of the circles along the y axis is arbitrary, and done for visual clarity). The red diamond and circle denote observed changes using CRU and BoM/AWAP data, respectively the coloured circles indicate individual ensemble members from various experiments. The horizontal black line through the two observational values indicates a range encompassing 95% of the values from the CONTROL distribution. b, The same as in a but for distribution of three-member ensemble means. The filled squares indicate ensemble-mean precipitation differences for 1981–2012 minus 1911–1970 for various experiments. c, The same as in a but for distribution of five-member ensemble means. The black square denotes the ensemble-mean precipitation difference in the ALLFORC experiment for 1981–2012 minus 1911–1970.

Change history

Corrected online 17 July 2014
In the version of this Letter originally published online, in Fig. 2a and b the text labels relating to the years were swapped. This has now been corrected in all versions of the Letter.

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Affiliations

  1. GFDL/NOAA, PO Box 308, Princeton University, Princeton, New Jersey 08542, USA

    • Thomas L. Delworth &
    • Fanrong Zeng

Contributions

T.L.D. designed the simulations, conducted most of the analyses and wrote the manuscript. F.Z. conducted the simulations including data post-processing, and contributed to the analysis and writing of the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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