Met Éireann has now issued drought warnings for Ireland. Hosepipe bans have come into force for Northern Ireland and the Greater Dublin Area (GDA) of the Republic of Ireland. As a result, the big news now is likely to be "drought" in both countries. If the lack of rainfall continues, it is highly likely that the UK Met Office will also begin issuing drought warnings. What is a drought exactly though?
As far as I see it, there are two kinds of droughts.
Absolute drought - I like to personally call this a "short-term drought" rather than absolute drought because it leads to less confusion with the other kind of drought. A short-term or absolute drought comprises of at least 15 consecutive days with 0.2mm of rain or less. An absolute drought varies on return period for each place. For example, England & Wales are more likely to receive absolute droughts than Ireland and Scotland. Examples of recent absolute droughts include November/December 2016 and July 2013.
Long-term drought - A long-term drought does not have a specific definition but in general, it can be described as a year or more with a lot of below average precipitation months. Long-term droughts can last very long depending on how weather patterns establish themselves. Examples of recent long-term droughts include 1995-97, 2004-06 and 2010-12. Unlike absolute droughts, long-term droughts can be difficult to break and they require several runs of very wet weather in order to not be a drought anymore as such happened in Autumn 1976 and April 2012 onwards.
Here are some notable absolute droughts that Dublin Airport has recorded since it began record keeping in 1941.
7 August - 6 September 1947 (31 days)
4 July - 1 August 1955 (29 days)
19 April - 13 May 1984 (25 days)
8 April - 1 May 1982 (24 days)
6 - 29 June 1992 (24 days)
The August-September 1947 absolute drought was as a result of one of the most prolonged easterlies to ever be recorded in the British Isles - the longest being the January-March 1947 easterly (fascinatingly in the same year) which of course culminated in the phenomenally snowy and cold Winter of 1947.
Some of the UK absolute droughts have been far worse than this Irish 1947 drought though and examples include:
4 March - 15 May 1893 (73 days) at Mile End, London
14 August - 9 October 1959 (56 days) in parts of eastern England
30 July - 17 September 1947 (50 days) in Kent
June 2018 has officially recorded an absolute drought for parts of the UK, especially over southern England but others like Ireland have yet to reach the official criteria in spite of drought concerns. The issue for them being was that usually when rain fell, they came in small amounts. However, since June 21, an anticyclone has kept things bone dry and we're vulnerable to absolute drought as a result.
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