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Flood risk rises as La Nina becomes 'active event'

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The Bureau of Meteorology has today declared Australia’s first active La Nina since the flood-causing event a decade ago triggered one of the wettest two-year periods for the country on record.

Manager of Climate Operations Andrew Watkins says a La Nina typically brings more tropical cyclones than normal and also increases the chance of rainfall and floods across parts of the country.

“Typically, La Nina brings more rainfall, particularly across northern Australia and into eastern Australia as well, and as that wets up the soils it does increase the risk of flooding whenever we get a big rainfall event,” he said today.

The last event started in 2010 and extended into 2012, triggering insurance catastrophe events such as Tropical Cyclone Yasi and the Brisbane flooding.

“This year though, we are probably not going to have something as extreme as that event,” Dr Watkins said.

Dr Watkins says events more typically fade out in the autumn and the current La Nina is likely to be a little more moderate.

The bureau’s shift today from a La Nina alert to a declaration of an active event follows changes in ocean temperatures and weather patterns over the Pacific Ocean.

Recent observations and model forecasts show the central tropical Pacific is now 0.8°C cooler than normal, and that has resulted in changes to trade winds and pressure patterns. Climate models suggest these patterns will continue until at least the end of the year.

The bureau previously shifted from a watch to an alert on August 18, while the US National Oceanic and Atmospheric Administration declared an active La Nina status earlier this month.

Dr Watkins says the typical weather patterns associated with La Nina may help to reduce the risk of severe bushfires this summer in southern Australia.

“We can’t avoid some fires in any summer now. La Nina, though, with a bit of extra rainfall hopefully will keep those fires a little smaller, a little shorter than what we have seen in recent years,” Dr Watkins said. “It reduces the bushfire threat a little bit, but doesn’t extinguish it entirely.”