Met Éireann has explained why the country experienced one of the warmest and wettest Decembers on record — and warned that “severe weather events” could become more frequent and even more intense.
The national meteorological service said an unusually high frequency of southerly or south-westerly winds persisted throughout last month and the warm and moist tropical air masses brought very mild, wet, and stormy weather.
“December 2015 was one of the mildest on record in most areas and the wettest on record in parts of the West, South, and Midlands,” it said. “The widespread flooding in some parts of the country was exacerbated by already saturated ground following above- normal rainfall in November. The combined rainfall totals for November and December were the highest on record in some parts of the country, in particular at Shannon, Cork, and Knock airports.”
Met Éireann said jet streams play a key role in determining the weather.
“Jet streams generally don’t follow a straight path but normally have peaks and troughs,” it said. “This December there was a pattern of continuous troughs and ridges across the North Atlantic and over Ireland, giving us a mild, predominantly south to southwesterly airflow. This resulted in a prolonged spell of very mild and very wet weather, during which record temperatures and rainfall amounts occurred.”
It said an “atmospheric river” formed on a stronger than normal jet stream, which resulted in large quantities of rainfall falling over parts of Ireland during Storm Desmond.
The forecaster said it is very difficult to determine the exact causes of the recent extreme weather: “Some studies suggest that the El Niño event in the Pacific is likely to increase the risk of strong jet streams, heavy rainfall, and stormy conditions during winter,” it said. “Climate change models suggest that with rising temperatures leading to an increase in the water-carrying capacity of the atmosphere, we can expect an increase in the frequency and intensity of severe weather events.”
It said climate must be assessed over decades before genuine trends can be identified, as opposed to natural variability: “At present we can point to the unusual persistent strong west-south-westerly air flow over the country as the predominant causes of the extreme weather this December, without attributing a definitive cause.”
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