Sunshine related variables

Sunshine hours

 
 

Figure 45 - Total sunshine hours for each year for Scottish regions from 1929 to 2004, with smoothed curves showing a running average. The dashed vertical line marks 1961.

Table 22 - Changes in total sunshine hours (as a percentage), from 1929 to 2004 and 1961 to 2004.

 

1929 to 2004 1961 to 2004
North Scotland East Scotland West Scotland Scotland North Scotland East Scotland West Scotland Scotland
Spring -5.6 0.5 -4.4 -3.3 4.5 6.9 2.7 4.7
Summer -3.1 1.1 1.9 -0.2 -2.1 0.2 -1.4 -1.1
Autumn -3.0 4.5 8.3 2.8 17.9 12.1 11.0 13.8
Winter -13.8 -0.4 -0.3 -5.1 -4.6 12.8 -0.6 2.6
Annual -5.6 1.2 0.2 -1.6 2.7 5.5 1.6 3.3

 

Regional trends

 

  • The average number of hours of sunshine recorded each day is lowest in North Scotland but this is also the region that has seen some of the largest changes.
  • Only North Scotland shows any obvious trends (winter and annual sunshine hours have reduced) and then only over the longer analysis period, in other words, since 1929.
  • Since 1961, the average number of sunshine hours in a day has increased by a small percentage each year in all three regions. This seems largely due to a large increase in sunshine in the autumn months. Since we have not seen a trend any change may be simply be part of natural variability.
  • East Scotland has become sunnier in all seasons since 1961 but again there is no obvious upward trend.

Spatial trends

 

  • There is wide variation in the patterns of change in sunshine across Scotland for each season for the 1961 to 2004 period.
  • There has been only slight change over this period in either spring or summer and the main changes have taken place in the second half of the year.
  • In some areas the changes are large, for example, up to a 40% reduction in sunshine hours in winter (December to February) in parts of North and West Scotland. As the patterns are in small areas only these changes are not apparent in the regional and national averages.

Future trends

 

  • The UKCIP02 scenarios report did not include an estimate for future sunshine hours, so it is not possible to compare trends with those expected for the future.
  • However, sunshine hours may be related to cloud cover. By the 2080s, the UKCIP02 scenarios estimate cloud cover may increase slightly in winter, particularly in the northern half of Scotland, and that it may reduce in all other seasons, with the greatest changes in summer in the southern and eastern areas.
  • The reduction of winter sunshine hours we have already seen is, to some extent, consistent with this.

Figure 46 - Patterns of change in sunshine hours (as a percentage), between 1961 and 2004, for each season.