Summary/Abstract
On the 17th and 18th October 2023, Storm Babet brought record rainfall amounts to the south of Ireland, leading to significant flooding. The intense 2-day rainfall fell on soils saturated by over 3 months of above average rainfall.
In this event attribution study, the authors find that 2-day October rainfall at least as high as that which occurred during Storm Babet has more than doubled in likelihood and the intensity of such rainfall events have increased by around 13% due to global warming since pre-industrial levels. The authors note that this result has high confidence, with agreement between models and observations. However, the study also finds that the observed pre-storm rainfall between July and September 2023, which contributed to the severity of the storm, may have become less likely by about 25% due to climate change, although this secondary result has very low confidence due to high uncertainties across all datasets and the disagreement in the direction of change between models (drying) and observations (wetting).
The authors further find, with high confidence, that at 2 degrees of warming will further increase the likelihood and intensity of such events. However, the study notes that these projected changes are challenging to quantify due to model uncertainties, and so the author’s reported results of a 20% increase in likelihood and 2% in intensity at 2 degrees of warming have low confidence.
Finally, the study finds that significantly worse flooding was only prevented due to the fortunate circumstance that the storm coincided with a spring low tide. The authors note that, had the event occurred at high tide and/or with substantial storm surge, flooding could have been much more extensive, and that Midleton proverbially ‘dodged a bullet’ of a far worse disaster thanks to the chance spring low tide at the time of the peak river flow.