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When garden swimming pools are uprooted and washed into the sea, you know a storm is serious. That’s what has happened in Sydney, with the city battered for two nights by ferocious winds, torrential rain and waves up to 8 metres high.

Four people have been killed, and there has been widespread damage, flooding and disruption as the storm heads south, with .

Luxury properties in Collaroy Beach have lost half their backyards – as well as that swimming pool – and the beach itself has narrowed by 50 metres.

Ian Turner, director of the Water Research Laboratory at the University of New South Wales, says sand levels on the beach dropped by between 2 and 5 metres, with 150 cubic metres washed back into the sea from every metre of the shoreline.

The Australian Bureau of Meteorology that the storm would be unusually fierce because of a of the highest tides – called king tides – and the usual seasonal low pressure zones called east coast lows that routinely develop at this time of year.

In a , Acacia Pepler, who studies the effect of climate change on east coast lows at the University of New South Wales Climate Change Research Centre, said that there are usually seven or eight such lows per year. Her modelling studies suggest that the current storms aren’t a result of climate change.

If anything, east coast lows will decline overall by 25 to 40 per cent by the end of the century, she says. But they may have a larger impact, becoming more frequent in warmer months, occurring closer to inhabited shorelines, and be boosted further if sea levels continue to rise. “That means more properties are vulnerable to storm surges,” she writes.