Irish Hurricane Study Shows 40pc Increase In Rainfall With Just One Degree Of Ocean Warming

Irish researchers have discovered a terrifying link between warming seas and massive increases in the amount of rain dumped on land by hurricanes.

They found that just a 1C increase in ocean temperature increases hurricane rainfall by 40pc, making hurricanes all the more deadly by adding freshwater flooding to already devastating winds and coastal surges.

Their discovery helps explain why several hurricanes that hit the US in recent years were more destructive than anticipated, particularly over inland states not affected by coastal flooding.

It also provides advance warning for Ireland where hurricanes and ex-tropical cyclones hit much less frequently but are feared will increase under a changing climate.

“The implications are that if more ex-tropical storms hit Ireland in the future, they could bring more heavy rain and associated flooding,” said lead author Dr Samantha Hallam of the Icarus Climate Research Centre at Maynooth University.

“We had Lorenzo in October 2019 which caused extensive flooding in Ireland and that was an ex-tropical cyclone.

“Another example is Hurricane Ophelia in 2017 which also brought heavy wind and rainfall so we have experience of this before.”

There are further worrying results from the research as it shows that, over the course of a year, a 1C rise in sea temperature leads to a much wetter year overall, with a 140pc increase in total rainfall.

A satellite image on September 26, 2022, of Hurricane Ian over the US. Photo Nasa via AP.

The Icarus team studied 392 hurricanes that hit the US from 1998 to 2017, tracking the impact on nine eastern and southern states from New York to Texas.

Dr Hallam said their interest was sparked by Hurricane Harvey in 2017, a storm that matched Hurricane Katrina for ferocity, but which was wetter than anything else on record in the US.

It caused more than $100bn in damage, around half of which was to properties not insured against floods.

Scientists already knew that temperature rise increases evaporation rates, causing more moisture to be sucked up into the air and to fall in more intense cloudbursts, but the increase has generally been measured at around 7pc.

Dr Hallam said this was because the measurements were largely taken at sea.

“What we’re seeing is a different response over the ocean and over land,” she said.

“Other studies have found the increase over the oceans but no one has really looked at the difference between the ocean and the land response, and obviously the response on land is what’s important for flooding.

“Lots of people have done studies on the wind impacts and storm surge, but what we’re finding now is that some hurricanes are going quite a long way inland and they’ve got this new risk of freshwater flooding.”

The Icarus study focused on the North Atlantic region where the hurricanes studied formed and examined sea temperature records there over the 21 years.

Sea temperature can vary from year to year but the underlying trend with climate change is for increased warming.

The finding that a one degree increase in sea temperature led to a 140pc increase in total annual rainfall was attributed to a combination of wetter hurricanes, an increase in the number of hurricanes and a general increase in rainy days.

Dr Hallam said the findings may not hold true for all parts of the world as there were unique characteristics to the North Atlantic but she said further study was warranted.

She also said the findings should be heeded by homeowners, insurers and policymakers.

The research was supported by the Marine Institute with funding from the government and assistance from the University of Reading and the National Oceanography Centre in the UK.

The full study is published in the current edition of the scientific journal, Environmental Research Communications.

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(Source – Irish Independent – Environment – Caroline O Doherty – 03/03/2023)

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