Precipitation related variables

Average precipitation totals

 
 

Figure 28 - Precipitation total (in millimetres) each year for Scottish regions, from 1914 to 2004, with smoothed curves to show a running average.

Figure 28 - Precipitation total (in millimetres) each year for Scottish regions

 

Table 15 - Changes in average precipitation totals (as a percentage), from 1961 to 2004 and 1914 to 2004. Values in bold show that we are 95% confident (statistically) that the change is part of a measurable trend.

 

  1914 to 2004 1961 to 2004
North Scotland East Scotland West Scotland Scotland North Scotland East Scotland West Scotland Scotland
Spring 13.9 6.1 22.0 14.3 16.2 9.4 17.3 14.8
Summer -12.7 -18.9 -7.5 -12.7 -7.0 0.2 7.3 -0.6
Autumn 13.6 0.7 15.6 11.1 5.3 22.2 5.9 9.1
Winter 20.9 -0.8 9.0 11.6 68.9 36.5 61.3 58.3
Annual 9.6 -3.5 9.5 6.2 21.0 18.4 23.3 21.1

 

Regional trends

 

  • In each region, and across the country, the change in winter precipitation since 1961 shows a clear upward trend. We can see an increase of almost 70% in winter precipitation in North Scotland.
  • The average precipitation each year also shows a trend towards much higher totals over the same period. Scotland has become 20% wetter between 1961 and 2004.
  • But there has been little or no change in average summer precipitation totals in each region. Changes in summer precipitation show no clear trend over the 1961 to 2004 period.
  • Looking at the 1914 to 2004 period, the pattern of change is less clear and we can see only two trends - a reduction in summer precipitation in East Scotland and an increase in spring precipitation in West Scotland.
  • The average precipitation each year has increased across most of Scotland since 1914, but there has been a slight reduction in both average annual and winter precipitation in East Scotland. This is the opposite of the trend measured over the period 1961 to 2004.

Spatial trends

 

  • The largest changes have taken place in winter months across all but the most eastern areas of Scotland. In some areas of the west Highlands and the Hebrides, winter precipitation has more than doubled since 1961.
  • The pattern of change is completely reversed in autumn, with eastern areas being the only widespread region to become wetter, with increases of more than 20%.
  • In summer, northern areas of Scotland have become drier since 1961, particularly the north-west. This reduction in summer precipitation is more than 20% in some areas.

Future trends

 

  • The UKCIP02 scenarios show relatively little change to average precipitation amounts each year (the trend we have measured shows increasing totals) but winter months may become wetter (as already seen) while summer months may be drier than at present (we have seen little change so far).
  • The pattern of change may not be the same across Scotland. UKCIP02 estimate eastern Scotland may experience the most extreme percentage changes in precipitation (going against the trend we have seen already), with an increase in winter and a reduction in summer.
  • As with the trends of temperature change, there are similarities between the precipitation trends over the longer 1914 to 2004 period and the expected changes in the future. Over the longer period, the summer months have become drier and there has been relatively little change to the average values each year.

Figure 29 - Patterns of change in precipitation totals (as a percentage) between 1961 and 2004 for each season.

 

Figure 29 - Patterns of change in precipitation totals (as a percentage) between 1961 and 2004 for each season.