Extreme rainfall variability in eastern Australia

The non-linear relationship between ENSO (SOI) and maximum 5-day rainfall (Rx5day) in eastern Australia. Note that 2010-11 is the strongest La Niña in the record and had the third highest area-averaged extreme rainfall total.

 

Eastern Australia has a strongly variable climate on inter-annual and multi-decadal timescales. This region can experience severe flooding, such as occurred in Queensland in 2011, and also harsh droughts.

Climate variability in this area is strongly related to variability in the Pacific Ocean. The El Niño-Southern Oscillation (ENSO) strongly modulates extreme rainfall in eastern Australia with more intense extreme rainfall events occurring during La Niña seasons than in El Niño seasons.

This study shows that this relationship is non-linear such that the strength of La Niña events has a far greater effect on the intensity of extreme rainfall than the strength of El Niño events does (see figure).

However, we also found that there is strong multi-decadal variability in this non-linear ENSO-extreme rainfall relationship associated with the Interdecadal Pacific Oscillation (IPO). During cool IPO phases, such as we've had in the past few years, extreme rainfall events are intensified in strong La Niña events. In warm IPO phases, the most recent of which occurred in the 1980s and 1990s, there are fewer strong La Niña events and also less intense extreme rainfall.

The causes of the non-linearity in the relationship between ENSO and extreme rainfall are not entirely clear. The mechanism appears to occur on a large-scale and there is a signal for enhanced convergence of moisture fluxes near the surface in stronger La Niña seasons over areas of eastern Australia. More research is needed on this topic.

Paper:

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