Warmer, wetter weather on the horizon

While the average rainfall in Ireland doesn’t change massively year on year, there can be a lot variability between different months in different years, according to Sandra Spillane, who works as an Observational Climatologist with Met Éireann.

“Looking at the overall rainfall over the last five years there has been on average little or no change in January or April rainfall - however, the trend towards wetter Februarys is observable, with large variability between years in February. For example, February 2023 was the sixth driest February and February 2020 was the wettest February on record.”

She also says that for some months, there was an observable trend of decreasing rainfall.

“In March over the last 50 years,, we see a large variability in rainfall. While there is a decreasing trend; despite that, March 2023 was the wettest March on record.”

Despite the variability, Sandra says that months that were both traditionally dry and traditionally wet have largely remained so.

“In Met services around the world we look at long term averages, looking at weather patterns for a minimum of 30 years,” she explains.

“Looking at the latest figures from the period from 1991 to 2021, the driest months are still April and May. The wettest months are still October, November and January, and August is the wettest summer month.”

There can still be massive variation in those months: “In July 2023, there was a national average of 203mm. That amount is what usually falls from October to February. Things like that have happened in the past, for example in June 2012 at over 200mm on average; in August 1985, there was 216mm.

"It’s rare but we do see monthly averages during summer to have huge variability.”

While on the surface some months look to have steady levels of rainfall, delving further into the data can show huge differences in the amount of rain that falls from year to year, according to Sandra.

“There have been some changes in long-term rainfall over the last 50 years. Some months don’t seem to becoming drier or wetter - for example April is a straight line trend on average. But the monthly total for April has varied from 13mm to 150mm.”

Sandra also suggests that while some months have seen their monthly average increase, there is no guarantee that every year will be the same.

“We can expect trends for some months for increased in rainfall events to continue. For example we’ve seen wetter than normal weather this October, and October 2022 saw 220mm of rain, making it the wettest on record.

"But October 2024 might be a dry one because in the last decade we’ve had drier than average ones as well, but we always have to be prepared for them.”

Flux

Sandra says that all of this flux in weather is a sign of climate change.

“With climate change, rainfall is expected to become more variable, and there are projected increases in the frequency of both heavy rainfall events and dry periods.

“As our planet warms, so does our atmosphere, and warmer air can hold more moisture. In Ireland, average annual rainfall has increased by about 7% over the last 30 years over the previous 30 years. Heavy rainfall events are expected to increase and there are some signs already of that in Ireland.

She concludes by saying that climate change is likely to lead to an increase in emergency weather situations such as those seen in the south of the country recently.

“Compound events are when two or more weather or climate events occur at the same time, or in the same area or both. For example, coastal flooding arising from heavy precipitation combined with storm surge is a key type of compound event relevant for Ireland.

"The flooding event in Midleton was an example of such a compound event. With climate change, the likelihood of storm surge combined with heavy precipitation is projected to increase with additional warming.”