Since 1950, rainfall over southern and eastern Australia has decreased, significantly reducing inflows to the Murray and Darling rivers, Australia's longest river system. In particular, precipitation in late austral autumn has decreased by about 40 percent from the long-term seasonal average for Victoria, Australia's most densely populated state.
To learn more about these rainfall changes, Cai and Cowan compare precipitation data from Australia with global data sets and find that the reduction occurs predominantly in May, with rainfall variations linked to two sources of sea surface temperature (SST) variability.
First, higher SSTs in the waters off Indonesia, which occur as the Indo-Pacific system enters into La Niña-like conditions, is associated with a rainfall increase over northern Victoria; a reduction in La Niña events and an increase in El Niño conditions since 1950 likely contributed to the observed rainfall decline.
Additionally, SST variation patterns in the Indian Ocean are linked to atmospheric wave trains, with a low-pressure center over Victoria that helps promote rainfall. However, these wave trains have weakened since 1950, also contributing to the observed rainfall decline.
Title: Dynamics of late autumn rainfall reduction over southeastern Australia
Authors: Wenju Cai and Tim Cowan: CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia; also at Wealth from Oceans National Research Flagship, CSIRO, North Ryde, New South Wales, Australia.
Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033727, 2008; http://dx.doi.org/10.1029/2008GL033727
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