El Niño & la Niña: impact on Australia

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The interaction of El Niño, La Niña (ENSO) and the Indian Ocean Dipole on Australia

The natural climate variability can sometimes interact in complex ways, influencing one another.

Such natural climate oscillation makes for considerable variability from one year to the next: for instance, in southeastern Australia and in the Murray-Darling Basin, monthly rainfall can increase by up to 25 mm during a concurrent La Niña and negative IOD event.

When an El Niño phase coincides with a positive IOD phase, this same region is hit by severe drought. However, a precipitation deficit or surplus can also ensue in the eastern half of Australia when an El Niño or La Niña event occurs on its own during a neutral IOD phase.

Effect on bushfire risks in Australia and New Zealand

Climate oscillations also affect the risk of bushfires: in southeastern Australia, particularly in Victoria, the risk is higher during positive IOD phases and during El Niño events. There is a steep rise in the risk of bushfires here when these two climate conditions occur simultaneously. In the eastern parts of the New Zealand islands drought episodes primarily occur during summer El Niño events. Winds from the west prevail during these periods, bringing precipitation to the western coasts and dry weather to eastern parts. There is a greater risk of forest fires during these phases.

The influences of El Niño and La Niña on precipitation in Australia

El Niño and La Niña also have a dominant influence on the development of intense precipitation events in Australia. This emerged, for instance, during the recent intense precipitation events between 2010 and 2013.

During La Niña phases and negative IOD phases and when the two phases coincide, there is a greater risk of heavy rainfall in the eastern half of Australia. However, 10 to 20% of the heavy rainfall events which hit the Brisbane area between 2010 and 2011 can most likely be attributed to higher sea surface temperatures in the north. Indeed, it is possible that we are already seeing the additional influence of climate change in Australia.

Predictability of natural climate variability

El Niño, La Niña and IOD phases can be forecast on a seasonal basis. Based on climate models, institutes provide forecasts with a moderate predictive skill for lead times of about four to six months, these forecasts are much better at predicting the sign of an imminent phase than at predicting the intensity. Australia's Bureau of Meteorology provides an overview of forecasts on its website, for instance.

Impact on insurers

Improved forecasting of natural climate variability means that insurers' risk management teams can prepare more efficiently for regional changes in weather-related loss probabilities. For one thing, it helps them to plan sufficient human resources for loss adjustment and to ensure that appropriate emergency plans are in place.

The knowledge about climate phases could also be used to inform and raise awareness among policyholders and the general public, providing knowledge-based incentives to take preventive measures: for example in response to risks in potential floodplains or bushfire areas, where it is essential to ensure an adequate distance from vegetation.

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