Diurnal climate change: a case study from the Durham Observatory

Installation of an automatic weather station at the Durham Observatory in 1999 has allowed analysis of hourly air temperatures and hourly rainfall. Changes in mean air temperature and in the diurnal cycle to 2023 are analysed. Analysis of hourly rainfall totals is also presented. The use of data from the UK Environmental Change Network’s Moor House weather station allows comparison between lowland Durham and an upland location in the Pennine Hills. Durham has become warmer and wetter, particularly in the most recent period studied. Moor House also has clear signs of warming but there has been no significant change in rainfall. The mean hourly temperature difference between the two sites has increased: from 3.12 °C in the 2000s, to 3.39 °C in the 2010s to 3.48 °C in the 2020s. The mean difference in hourly rainfall totals has fallen from 0.161 mm in the 2000s, to 0.148 mm in the 2010s and to 0.144 in the 2020s, showing that rainfall totals have increased at the lowland site compared to the uplands. Recent changes in temperature and rainfall at Durham are seen in the afternoon, perhaps indicating the generation of cloud and rain because of increased air temperatures which are likely to render the air more unstable. This change in afternoon rainfall is not seen at Moor House, perhaps indicating that warming has less effect at an upland location where orographic uplift is the dominant mechanism for generating precipitation.