An analysis of rainfall across the British Isles in the 1870s

Monthly records for the period 1871-1970 from 91 stations across the British Isles are used to place very high rainfall totals during the 1870s, 1872 and 1876-1877 in particular, in context. Comparisons are drawn with 2012 and the winter of 2013-2014, both of which were exceptionally wet in parts of the British Isles. Traditional Lamb weather type count and objective measures of atmospheric circulation obtained from reanalysis of surface pressure charts are used to classify the weather conditions under which these very high rainfall totals were generated. The normally wettest locations in the British Isles, i.e. the uplands in the north and west, were not unusually wet in the 1870s, whereas locations with extremely high rainfall totals (relative to mean annual rainfall) tended to be further south and east in the lowlands. These exceptionally high totals were associated with a high frequency of cyclonic weather types and high scores for atmospheric vorticity; at the same time, the frequency of anticyclonic weather and of westerly winds tended to be very low. The winter of 2013-2014, remarkably wet in southern England, was somewhat different in that both the frequency of westerly air flow and the resultant flow were very high and so were vorticity and the frequency of cyclonic weather types; the year 2012 experienced similar atmospheric conditions. The results confirm the importance of cyclonic weather for large rainfall totals across much of the British Isles; strong westerly winds seem only to favour the uplands and northwest coastal locations.