Summer 2018 Analysis

An Analysis of the heatwaves and droughts that affected Ireland and Europe in the summer of 2018:

Droughts can occur in Ireland at any time of the year when high pressure dominates our weather over a long period of time. However, heatwaves only occur in Ireland in summer during high pressure dominated periods. High pressure systems or anticyclones, can stall over Ireland for long periods of time, pushing the North Atlantic Jetstream away to the north and blocking Atlantic weather fronts from coming over the country. This kind of pattern, when prolonged, can lead to dry soils in summer and when combined with a lot of sunshine, increases the temperature even further, due to the sun’s energy not being used up to evaporate water. The air mass most associated with this pattern is a tropical continental air mass, which can originate in North Africa.

The dry and settled weather from the end of May 2018 continued through most of June and July. Slow moving anticyclones positioned themselves either directly over Ireland, just to the north, or over Scandinavia. There were times when low pressure broke through, especially in mid June, but rainfall amounts remained low and the weather mostly dry with a lot of sunshine. August became more un-settled in the West and Northwest of the country, but high pressure to the southeast kept the South and East of Ireland drier and warmer than normal.

This prolonged settled spell of weather led to heatwave and drought conditions in many parts of Ire-land. Heatwave conditions were recorded at 15 synoptic stations for 5 or more days between the 24th June and the 4th July. Oak Park, Co Carlow had heatwave conditions for 11 consecutive days. During this period, Shannon Airport, Co Clare reached 32.0°C, the highest temperature ever recorded at a synoptic station in Ireland.

Absolute drought conditions were recorded at 21 stations at various times between the 22nd May and the 14th July. There were partial drought conditions recorded at 10 stations and dry spells recorded at 5 stations at various times between the 28th May and the 25th July. For the combined June and July period, all stations reported rainfall below the LTA. This was particularly the case in midland, eastern and southern areas, where between one third and one half of the LTA rainfall was reported. Cork Air-port had its driest summer on record (record length 56 years) and the Phoenix Park had its second driest June-July period since 1880. Indeed much of the South and East of the country had below aver-age rainfall for 6 continuous months between may and October 2018.

The summer of 2018 will stand out as one of the warmest and driest summers on record for Ireland and most of Northwestern Europe. The heatwaves and droughts experienced in Ireland during the summer of 2018 occur in the natural cycles of the weather and 1976 stands out as another summer where Ireland experienced exceptionally warm and dry conditions. However, when comparing the global temperatures of both June’s as an example, the clear global increase in tempera-tures from 1976 to 2018 is evident.

It is also clear from the ‘Warming Stripes’ produced by Professor Ed Hawkins (University of Reading) that the average temperatures globally and regionally are rising and that “the science on the human contribution to modern warming is quite clear. Humans emissions and activities have caused around 100% of the warming observed since 1950, according to the Intergovernmental Panel on Climate Change’s (IPCC) fifth assessment report” ((IPCC) fifth assessment report, Carbon Brief, 2017).
At the European Geosciences Union (EGU) General Assembly 2019 it was also stated that “2018 Northern Hemisphere concurrent hot extremes could not have occurred without human-induced cli-mate change” and “Observed 2018-like heatwave areas are simulated in models and are projected to occur nearly every year for a 2°C global warming scenario” (EGU General Assembly, 2019).
Climate projections for Ireland show a trend towards warmer, wetter, winters and hotter, drier, sum-mers.

Full report <<here>>