Temperature and surface lapse rate change: a study of the UK's longest upland instrumental record

A homogenized 76-year daily-mean temperature series is presented for Moor House, an upland peatland meteorological station in northern England, which provides the longest instrumental temperature record in the UK uplands. This paper assesses trends in the temperature record over time compared to the nearby lowland temperature record at Durham. Overall warming for 1991–2006 compared with 1931–1960 and 1961–1990 was approximately the same at the upland site (0.53 °C and 0.73 °C for the two time periods, respectively) as at Durham (0.61 °C and 0.71 °C), maintaining a similar lapse rate. However, winter warming is dominant at Moor House and more pronounced and concentrated over a shorter period than at Durham; summer warming is more prominent at Durham. Therefore, seasonal lapse rates have changed and become more divergent between winter and summer half-years. Rather than changes in the dominance of particular air-masses over the study area accounting for seasonal lapse rate changes, there had been significant steepening of lapse rates over time for some air flow types. Minimum temperatures have increased more than maximum temperatures at Moor House with a consequent significant reduction in diurnal range. At Durham minimum and maximum temperatures have changed in approximate tandem so that there is no significant change in diurnal temperature range. The frequency of air frosts reduced by approximately 23% (from 129 days per year to 99) at Moor House from 1991–2006 compared to 1953–1980, and this may have major implications for the functioning of terrestrial and aquatic systems in the region. These results demonstrate that while overall annual warming in the uplands and lowlands within particular regions may be similar, even where annual lapse rates have been maintained, the seasonal distribution of that warming may be quite different even over short distances and so lowland records are not a reliable indicator of regional upland temperature change.