Understanding Climate Risk

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Archive for June 3rd, 2011

Northern Victorian Flood Review Part III

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This is the third post covering the January 2011 floods in northern Victoria. Part I described how the floods unfolded and Part II described the hydrology of the Loddon catchment and how its history has affected flood behaviour. This final post covers the climatic influences on the floods. The floods themselves are discussed here, and affects on the family farm in Kerang are shown here.

Northern Victoria’s rainfall is influenced by the El Niño–Southern Oscillation (ENSO; spring–summer), Indian Ocean Dipole (IOD; winter–spring) and Southern Annular Mode (SAM; winter). Correlations of northern Victorian rainfall with simple indices are -0.51 for SOI May–Jan, ‑0.48 and -0.45 for two IOD indices May–Jan, and -0.25 for SAM for winter rainfall.Recent research has linked exceptionally wet conditions in south-eastern Australia with the combination of La Niña and a negative Indian Ocean Dipole (-IOD) (Ummenhofer et al., 2009; Ummenhofer et al., 2011).

The -IOD is associated with exceptionally warm waters off north-western Australia resulting in ‘north-west’ cloud bands that bring flooding rains into northern Victoria. The recent extended drought in Victoria has been characterised by an absence of these weather patterns. While central and north-western Australia have become wetter, this rainfall source has been conspicuously absent from south-eastern Australia.

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Written by Roger Jones

June 3, 2011 at 3:37 pm