Friday, 23 April 2010

Today marks the 15th consecutive day without measurable rain (defined as 'no daily rainfall equal to, or exceeding, 0.2mm/0.01 ins.'). Up until the 1980s this 15-day period was known as a 'drought'. However, the rise of the mocking tabloid press, the general decline in exactitudes, and comparisons with life-threatening water shortages in the Third World quite correctly brought about the abandonment of the term 'drought' by all but a few diehards.
Nevertheless, it's interesting to examine these lengthy dry spells. The previous one occurred here from the 16th September to 2nd October 2009 (a total of 17 days), but lack of rain is generally less common during the Autumn and Winter months. A good Summer often produces a prolonged period of dry weather. In 1959 this area had 37 consecutive dry days (15th August to 20 September) and in 1976 parts of southwest England had no measurable rain for 45 days. Perhaps surprisingly there was no 15-day dry spell in 2003, but the rainfall deficit for the period February to October in that year was well over 50%.
The Spring months seem to have the most frequent dry spells. In recent years there have been several in mid Spring. In 1995 there were 19 dry days (29th March-16th April), in 1997 it was dry from the 25th March to 17th April (24 days). A total of 27 dry days occurred between 21st March and 16th April 2002, and in 2007 there was dry weather between 31st March and 22nd April (23 days).
Is there any way of connecting dry Aprils to the following Summer? Fortunately the answer is no. In 1912, parts of London had no measurable rain during April and the following Summer was one of the coldest and wettest on record! By the way, the previous 4 mid Spring dry spells were equally divided between good Summers and decidedly indifferent ones.