The Queensland and NSW region hit by this year’s record flooding faces rising risks from changes in tropical cyclone intensity and behaviour over future decades, research co-authored by IAG’s Natural Perils team shows.

Double the area of land in cyclone areas along the east coast could be impacted by Category 5 cyclones and triple the area of land will experience extreme rainfall before the end of the century, the research indicates.

“We know that tropical cyclones have the potential to cause serious damage, particularly in areas that have not been built to withstand such extreme conditions,” IAG Executive Manager Natural Perils and Atmospheric Scientist Mark Leplastrier says.

“Through this research, we now understand that the expanding footprint of future cyclones will see large populated areas across southeast Queensland and northern NSW vulnerable to the impacts of destructive winds and inland flooding.”

The researchers suggest that the projections provide preliminary evidence that cyclones in the near and more distant future could produce impacts that could exceed current wind loading standards and building codes for the subtropical regions.

“Given that this area currently has lower wind loading standards than coastal areas to the north, it is critical that the building regulatory authority considers the rapidly changing risk for homes and structures being designed and constructed now,” it says.

The research, in partnership with the US National Centre for Atmospheric Research (NCAR), has been published in the Journal of Weather and Climate Extremes.

Recent observations showing a decline in cyclone activity since the 1980s are supported, with the decline anticipated to continue for another decade, but the modelling shows frequency will likely rebound towards the end of the century, and cyclones will typically maintain their severe intensity for longer.

The research paper Abstract says the challenge of assessing regional changes in tropical cyclones (TCs) and their future impacts, given the short historical record and limited sample size, is addressed using “large climate model ensembles”.

The large ensembles were examined for the Southwest Pacific basin, including the southern-most portions.

“Combined, our results point to rapidly increasing risks of damaging TC winds and major TC flooding, as well as a heightened risk of water ingress through wind-driven rain,” the Abstract says.

The approach could be explored for other regions and sub-regions such as the west coast of Australia, the US Gulf Coast, or Japan, and could also be explored for other high-impact weather events, such as mid-latitude cyclones, the researchers say.