The climate of Malham Tarn

The daily weather record at Malham Tarn is analysed for the period 1961-2000. In addition, monthly rainfall totals listed in British Rainfall are analysed for the period 1875-1906 and an annual rainfall series is reconstructed from 1860 to the present. Notwithstanding the sheltered nature of the Tarn House site, the Malham temperature record since 1961 fully reflects the regional, indeed global, pattern of warming, with an increase over the last four decades of 1° C in annual mean temperature. Winters show the greatest seasonal warming, and there have been noticeably fewer air and ground frosts in recent years. In contrast, there is no clear trend in rainfall totals over the study period, with several fluctuations between wetter and drier periods over the four decades. There has been a clear tendency towards drier summers and wetter winters recently; this stronger seasonality is reflected in the occurrence of heavy rainfall, with more winter days with heavy falls of rain in recent years, and, in marked contrast, far fewer very wet days in summer. In the late 19th century, total summer rainfall nearly equalled that received in winter, whereas by the late 20th century, winter rainfall was well in excess. During the study period there have been several droughts, with those in 1976 and 1995 being especially extreme. By contrast, rainfall totals in autumn 2000 broke all records.