British Weather Extremes: Rainfall / Precipitation
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Very heavy rainfalls in Britain can arise from:
A method of classifying heavy short-duration rainfalls was devised by Ernest Bilham in the 1935 edition of British Rainfall. He used a simple graph to classify such falls into three categories; noteworthy, remarkable, and very rare; each were related to their approximate frequency of occurrence (see Journal Meteorology 12(122), 1987, 268). Although more recent studies have used a classification based on regional variations in rainfall the Bilham formula remains the simplest and has the advantage of assuming that the impact of a flash flood is related to local topography and drainage, rather than to how frequently an extreme rainstorm is recorded. It is more realistic to relabel Bilham's three categories as: 'noteworthy', 'remarkable' and 'extreme', thus avoiding the misleading implication that such events have any regular return period. This is consistent with TORRO's classifications of tornadoes and damaging hailstorms, which are based on severity rather than estimated frequency. The problems associated with verifying extreme rainfall events such as the Calderdale cloudburst of 19th May 1989 (when 193 mm of rain was reported in two hours) highlight the continuing need for a dense network of raingauges throughout the country to complement radar coverage.
HIGHEST DAILY RAINFALLS FOR EACH MONTH OF THE YEAR
mm inches
JANUARY 238.4 9.39 Loch Sloy main adit Strathclyde 17 January 1974
FEBRUARY 196.6 7.74 Ben Nevis Highland 6 February 1894
MARCH 164.3 6.47 Glen Etive Highland 26 March 1968
APRIL 182.1 7.17 Seathwaite Cumbria 22 April 1970
MAY 172.2 6.78 Seathwaite Cumbria 8 May 1884
193* 7.60* Walshaw Dean Lodge West Yorkshire 19 May 1989
JUNE 242.8 9.56 Bruton Somerset 28 June 1917
JULY 279.4 11.00 Martinstown Dorset 18 July 1955
AUGUST 238.8 9.40 Cannington Somerset 18 August 1924
SEPTEMBER 190.7 7.51 West Stourmouth Kent 20 September 1973
OCTOBER 208.3 8.20 Loch Avoich Highland 11 October 1916
NOVEMBER 211.1 8.31 Lluest Wen Reservoir Rhondda 11 November 1929
DECEMBER 199.1 7.84 Dalness Highland 17 December 1966
Note: A listing of the highest daily rainfalls recorded in each British county was
published in Journal Meteorology, 12(122), 1987, 263-6.
SOME EXTREME RAINFALLS FOR SPECIFIED SHORT DURATIONS IN THE BRITISH ISLES 1870 TO DATE
DURATION IN AMOUNT OF LOCATION COUNTY DATE MINUTES RAIN (mm) 5 32* Preston Lancashire 10 August 1893 10 45 Carlton-in-Cleveland (North Yorks) 10 August 2003 12 51 Wisbech Cambridgeshire 27 June 1970 15 56 Bolton Greater Manchester 18 July 1964 20 63 Sidcup Kent 5 September 1958 20 63 Hindolveston Norfolk 11 July 1959 25 67 Pershore Worcestershire 11 June 1970 30 80 Eskdalemuir Dumfries & Galloway 26 June 1953 45 97 Orra Beg Antrim 1 August 1980 60 92 Maidenhead Berkshire 12 July 1901 75 102 Wisley Surrey 16 July 1947 75 95 Ilkley North Yorkshire 12 July 1900 90 117 Dunsop Valley Lancashire 8 August 1967 90 111 Miserden Gloucestershire 10 June 1970 100 116 West Wickham Greater London 22 July 1934 105 116 Sevenoaks Kent 25 June 1980 120 131 Knockholt Kent 5 September 1958 120 155 Hewenden Reservoir West Yorkshire 11 June 1956 120 193* Walshaw Dean Lodge West Yorkshire 19 May 1989 155 169 Hampstead Greater London 14 August 1975 180 178 Horncastle Lincolnshire 7 October 1960 * Approximate value |