Flooding like that seen across Ireland during Storm Chandra has become almost three times more likely due to climate change, according to new research by Met Éireann and the ICARUS Climate Research Centre at Maynooth University.
The researchers carried out a “super-rapid” analysis of rainfall linked to Storm Chandra. While the one-day rainfall from the storm itself was described as “not particularly remarkable”, the seven-day accumulated rainfall before and after the storm made the impact far more severe.
Their findings show that seven-day rainfall totals like those associated with Storm Chandra are now 9% higher than in the pre-industrial era. When global temperatures were around 1.3°C cooler, such an event would have been expected once every 150 years. Today, a similar rainfall event is likely to occur once every 60 years.
In other words, flooding of this scale has become around three times more likely.
The study also found that Storm Chandra struck when soils along the east coast were already saturated and river levels were high after days of heavy rain. This greatly increased flood risk, as the ground could no longer absorb additional water.
Dr Claire Bergin of the ICARUS Climate Research Centre said this is the second time this storm season that flooding has occurred because rainfall fell on already waterlogged ground.
She warned that as global temperatures rise, the atmosphere can hold about 7% more moisture for every 1°C of warming, increasing the risk of prolonged heavy rainfall.
“The increase in rainfall magnitude can be directly linked to human-caused pollution,” she said, adding that stronger flood defences alone will not be enough without tackling global warming.
ICARUS researcher Lionel Swan said the study shows that devastating floods no longer require an extreme single-day downpour.
“Even relatively unremarkable rainfall can now cause serious flooding if it occurs over several days on already saturated soils,” he said.
The findings closely mirror research carried out after Storm Claudia last November, reinforcing concerns that Ireland’s flood risk is rising rapidly as the climate continues to warm.