Coastal flooding could occur weekly if greenhouse gas emissions continue, scientists warn

Researchers used tide data from Sydney and found that the high sea levels that lead to flooding are now occurring nearly five times more often than they did 100 years ago.

As the Antarctic air hits south eastern Australia with a freak cold snap – scientists warn that coastal flooding in Sydney could occur on a weekly basis, if greenhouse gas emissions continue.

The warning comes in a new research published in the AGU journal Earth’s Future.

Lead study author Monash University PhD candidate Ben Hague, who is also employed by the Bureau of Meteorology (BOM) as a climatologist, said in recent years coastal flooding in Sydney occurred around eight days a year but projected future sea level rise could see this occur once a week on average by 2050.

“If high greenhouse gas emissions continue, 2100 will see this coastal flooding occurring in Sydney on most days regardless of the weather,” said Mr Hague, who is completing his PhD at the Monash University School of Atmosphere and Environment.

“Accompanying the increase in frequency will be an increase in the severity of inundation and an increase in the areas which experience flooding,” he said.

The research team, which includes climate scientists from Monash School of Earth, Atmosphere and Environment, used tide data from Sydney and found that the high sea levels that lead to flooding are now occurring nearly five times more often than they did 100 years ago.

One of the key factors that influence water levels around Sydney are the tides – the twice daily rise and fall of the sea due to the gravitational pull of the moon and sun.

Another key contribution, particularly for high sea levels are storm surges, which are temporary rises in sea levels due to low atmospheric pressure systems and strong winds.

“Coastal floods usually occur when high tides coincide with storm surges, however as sea level rise pushes the day-to-day tides even higher, we are seeing that flooding can occur simply due to very high tides alone,” said Mr Hague.

“In fact, we found 20% of all coastal floods in the last 20 years occurred as a result of the tides alone,” he said.

“This is a startling result given that minor coastal inundation due to tides alone did not occur at all before 1991.”

The study found the proportion of coastal floods occurring solely due to tides will increase further as sea level rise continues and accelerates.

It concludes that by 2050 nearly all coastal inundation events will be due to tides – storm surges and the day-to-day weather will just determine the severity (minor, moderate, or more extreme impacts).

The research team has developed a framework that can allow coastal managers to make informed, impact-based decisions about risk tolerance and apply their own sea level planning allowances to see what these mean for coastal flood risk.

“Our next step is to look beyond Sydney and extend this analysis to all of Australia,” said Mr Hague.

The heights of tides, frequency of storm surges and the general landscape shape vary around Australia so this will mean that the effects of sea level rise may be felt differently in different places,” he said.

“Investigating these will help identify the parts of Australia are most vulnerable and help people living in these areas manage the risks of continuing sea level rise.”

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