It's needless to say that the UK and Ireland are widely known as having rainy temperate climates but are these general impressions correct? As Met Éireann states for the Republic of Ireland:
The general impression is that it rains quite a lot of the time in Ireland, but two out of three hourly observations will not report any measurable rainfall. The average number of wet days (days 1mm or more of rain) ranges from about 150 days a year along the east and south east coasts, to about 225 days a year in parts of the west. Unlike the rain in many other countries, especially in the tropics, average hourly rainfall amounts in Ireland are quite low, ranging from 1 to 2mm. Short-term rates can of course be much higher: for example, an hourly total of 10mm is not uncommon and totals of 15 to 20mm in an hour may be expected to occur once in 5 years. Hourly totals exceeding 25mm are rare in this country and when they do occur they are usually associated with heavy thunderstorms.
Maybe we aren't as rainy as some would think, the statistics show otherwise to what the general impressions say. Nevertheless, it can still rain a lot at times courtesy of Atlantic depressions coming in on a strong Jet Stream overhead. Sometimes, the Gulf Stream or Atlantic Meridional Overturning Circulation (AMOC) can be slowed down and there starts to be a lack of these Atlantic depressions pushing in from the west of Ireland and Scotland. This can be down to many things that occur in the atmosphere to cause blocking over top of the British Isles, Scandinavia and or Greenland/Iceland. These repeated patterns over time, especially in Winter and Summer, can build up to drought conditions as the continuous lack of rain leaves the landscape to lose its iconic green colour. This is what is happening here in 2018. May 2018 was the driest May since 2011 in England and Wales with an England and Wales Precipitation (EWP) total of 52.0mm whilst it was the driest since 1991 in Ireland and Scotland. This EWP total is likely to have been skewed by localised heavy thunderstorms in the last week of May because many places and for much of the month, had it exceptionally dry. The statistics are not in when I'm writing this but June 2018 has been the driest June since 1925 for most places and for localised areas of England, it has been the driest June on record with regions being left bone dry all month whilst others have been under 5mm of rainfall all month too. For the sake of this blog post, I'm going to estimate that June 2018 was either under 20mm or 10mm for the EWP figure. I have taken the liberty in crawling through the archives to find comparable very dry May/June periods with the EWP dataset. The following Mays and Junes I have found below to be comparable with 2018. I also added on the CETs for the month in brackets because it's also clear that the warmth has added onto the drought conditions of 2018.
1995
May - 48.5mm (11.6°C)
June - 20.2mm (14.3°C)
1976
May - 62.1mm (12.1°C)
June - 18.7mm (17.0°C)
1975
May - 50.5mm (9.9°C)
June - 22.1mm (14.7°C)
1962
May - 64.3mm (10.3°C)
June - 17.8mm (13.7°C)
1949
May - 68.1mm (11.2°C)
June - 18.1mm (15.3°C)
1940
May - 41.4mm (12.5°C)
June - 20.9mm (16.4°C)
1923
May - 69.8mm (9.2°C)
June - 19.4mm (12.5°C)
1921
May - 46.5mm (11.5°C)
June - 10.3mm (14.7°C)
1887
May - 54.0mm (9.4°C)
June - 20.8mm (15.3°C)
1868
May - 36.7mm (13.5°C)
June - 16.5mm (15.5°C)
To narrow it down further, I think the most comparable years to 2018 are 1868, 1921, 1940 and 1976. Interestingly, three of these 4 summers were hot. July 1868, June and July 1976 were all very hot months with CETs of at least 2.0°C above average. July 1868 is also the last month in a year ending in "8" with a CET of 18.0°C, will 2018 break this trend? Other things out of interest, 1887 pops up in here with having a similar rainfall distribution in terms of EWP to 2018 and two other similar things with 2018 are:
- The end of May in both years contained a Scandinavian blocking area of high pressure bringing the winds in from the east across the British Isles.
- June 1887 recorded Ireland's all-time highest temperature of 33.3°C and 2018 could beat or get close to this when I'm writing this blog post.
1921 is an interesting one too in the pack. It had a hot July and rather warm June though August was on the cooler side. The year was exceptionally dry and to this day remains the second driest year on record for the EWP dataset behind only 1788. The dry nature of the weather started in February of 1921 though and 2018 didn't start until May so it's not really comparable in that case.
We have a long way to go to beat the droughts of 1995-97 and 1974-76 but the fact that our grass is already turning very brown with only two well below average rainfall months then it's not a good sign at all.
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