Rainfall at Bidston, 1867–1951

Abstract

AbstractThe 85 years (1867–1951) of rainfall record at the Liverpool Observatory and Tidal Institute, Bidston, are the longest uninterrupted series in NW. Cheshire. Their salient features are:(i) The mean annual rainfall in the calendar year is 28–68 in. with one exceptionally wet year, 1872, when 45.66 in. were recorded.(ii) The mean of the seasonal year is 28.74 in. In this case, although the standard deviation is larger than with the calendar year, the driest and wettest years are not so extreme.(iii) October, although it has been getting drier, is the wettest month, and April is the driest. The characteristics of the other months are scrutinized and compared following the computation of mean daily rainfall figures.(iv) The probability of a month being the wettest in any year is directly proportional to the cube of its mean rainfall.(v) The probability of a month being the driest in any year is inversely proportional to its mean rainfall.(vi) Spring is the driest season and autumn the wettest, summer having significantly more rain than winter.(vii) No significant correlation exists between one season's rainfall and any subsequent season's fall.(viii) There have been very few occasions of heavy rainfall, the maximum recorded in 24 hr being just over 2 in., and only three noteworthy falls. This is due to Bidston's geographical position, as it misses the most violent instability storms and is partially in the rain‐shadow of the Welsh mountains, which protect it from the heaviest depression rains.(ix) On the average there is an absolute drought once every 15 months and it is of 19 days' duration. Only two droughts have lasted longer than 26 days.(x) Frequency curve graduation of annual and seasonal rainfall proved disappointing, as few absolute conclusions relating to extreme values could be drawn from the figures owing to the large probable errors involved, with what, in a statistical sense, is a relatively short period of observations, only 85 years. Deductions based on such computed curves are, however, the best method of estimating rainfall probabilities.