Modelling monthly trends in sunshine hours for the United Kingdom and its regions

Abstract Since 2019 the U.K. Met Office has provided monthly observations, beginning in 1919, on hours of sunshine for the U.K. and its regions. Time series analyses of these data are reported in this paper, using a deterministic monthly trends model. For the U.K. as a whole, winter trend sunshine hours have increased by 23% from 1919 to 2022 and spring trend hours have increased by 12%. Summer and autumn trend sunshine hours, on the other hand, have increased by only 3% and 7% respectively. Consistent with this, trend increases have been significant for the months of November, December, January, and February and also for April and July, but June has seen a significant decline in trend sunshine hours. Analysis of the regional data reveals a rich pattern of trend behaviours. The winter months have typically seen the largest increase in trend sunshine hours, the summer months the smallest, with Northern Ireland and the Scottish regions all experiencing falls in trend sunshine in June. The eastern regions have generally seen the largest increases in trend sunshine hours, often being associated with quadratic trends, the western and outlying regions the smallest.