Mapping the geographies of British rain

Professor Simon Naylor, Professor of Historical Geography, University of Glasgow

Much of the information about the nature of British weather in the 19th century came from voluntary scientific associations, which continued to be the case even after the establishment of the Meteorological Department of the Board of Trade (later the Meteorological Office) in 1854. This was certainly true in relation to the study of British rain. In 1863, George Symons, a young clerk at the Meteorological Department, resigned his post to devote his life to the organisation of a network of volunteer rainfall observers, which he ran from his home in Camden, north London. At the time of his death in 1900, Symons’ rainfall organisation numbered around 3,500 rain gauge stations across the British Isles. The British Rainfall Organisation, as it became known, was taken over by H Sowerby Wallis, Symons’ understudy, and Hugh Robert Mill, the Scottish geographer. Mill ran it alone from 1903, when Wallis retired due to ill health. One of Mill’s last acts as Director in 1919 was to negotiate the merger between the British Rainfall Organisation and the Meteorological Office. Nineteenth-century meteorology experienced what the historian of statistics, Ian Hacking, has called an “avalanche of printed numbers.” Tables of daily, monthly and annual rainfall were sent to Symons and his colleagues, and rainfall archives quickly accumulated in London and Edinburgh. What to do with all these numbers? Organisers encouraged the application of basic statistical techniques, notably the calculation of the arithmetical mean, for rainfall series. Alexander Buchan, the Secretary of the Scottish Meteorological Society, noted the problems of calculating reliable rainfall averages, especially given the capriciousness of rain’s occurrence. Trustworthy averages could only be calculated on long runs of annual observations. How then to produce averages of rainfall at stations with short runs of observations; how to compare stations’ averages that had been generated from different numbers of years of observations; and how to distinguish errant returns from those that were the result of unusually heavy rain, or no rain at all? Sir William Napier Shaw, Director of the Meteorological Office, noted that 19th-century meteorologists were engaged in the graphic representation of accumulating observations. The answer to meteorology’s numbers problem was, in other words, the rainfall map.

As a pioneer in the application of cartography to meteorology, Buchan transferred rainfall averages onto maps of the British Isles and represented them using shadings that mapped mean annual rainfall. Some of his maps – notably those representing Scottish rainfall – incorporated shading to indicate elevation contours, making the maps more visually complex but more useful for the exploration of relations between altitude and precipitation. Like Buchan, Hugh Robert Mill promoted the mapping of rainfall data. As the Director of the British Rainfall Organisation, Mill developed what he called “cartometric hyetography,” which transformed a slow and tedious process of inspecting printed forms into a “simultaneous and almost automatic” process of visual inspection. For both Buchan and Mill, the mapping of rainfall visualised errors and brought numerical data to life. The mapping of rainfall also had a practical importance. Many of the maps produced by the British Rainfall Organisation had been produced as part of commissions for municipal or statutory authorities, for legal arbitrations, as evidence for Parliamentary Committees, for insurance disputes (investigation of floods and their impacts), and to supply information to reservoir builders and water boards. With Mill’s retirement as Director of the British Rainfall Organisation, Symons’ leasehold house in Camden was given to the Royal Meteorological Society along with an endowment fund. The fund was used to research and prepare a rainfall atlas, published in 1926 as the Rainfall Atlas of the British Isles, with an introduction by Mill. It featured two main sets of maps. There were the small-scale maps of annual rainfall for each individual year from 1868, expressed as a percentage of the average for the period 1881–1915. These maps revealed years of excess and low rain relative to the mean. The second set featured maps of average monthly rainfall. Writing in Nature, Ernest Gold, the Deputy Director of the Meteorological Office, praised the average monthly maps for their practical utility but complained that “they do not make quite the same appeal to the imagination: averages never do.”

Further Reading

E Gold (1927) An Atlas of Rainfall (Nature).

H R Mill (1908) Map-Studies of Rainfall (Quarterly Journal of the Royal Meteorological Society).

Royal Meteorological Society (1926) Rainfall Atlas of the British Isles (London: Royal Meteorological Society).