Precipitation related variables

Days of heavy rain each year


Figure 32 - Days of heavy rain (equal to or more than 10 millimetres) for Scottish regions each year, from 1961 to 2004, with smoothed curves showing a running average.

Table 17 - Changes in days of heavy rain (equal to or more than 10 millimetres), in days, from 1961 to 2004. Values in bold show that we are 95% confident (statistically) that the change is part of a measurable trend.


North Scotland East Scotland West Scotland Scotland
Spring 1.8 1.0 1.6 1.5
Summer -1.4 -0.5 0.9 -0.4
Autumn -0.2 2.3 0.1 0.7
Winter 8.3 3.5 8.2 6.7
Annual 8.2 6.2 10.6 8.3


Regional trends


  • We can see a trend of increasing heavy rainfall in winter. In particular, North and West Scotland have seen an increase of more than eight days.
  • In all other seasons the changes are small and we cannot see a trend.
  • By looking at the graph showing the number of days of heavy rainfall and the one showing the average total precipitation in each year we can see a link, implying that the years with highest total rainfall are also the years with the most days of heavy rainfall, and vice versa.

Spatial trends


  • The patterns of change are broadly similar to those for total precipitation with a strong east-west gradient in winter months.
  • Most of the west has seen an increase in winter of more than five days of heavy rainfall.
  • Changes in summer months are small and do not show any trend. This is consistent with the findings of Osborn et al. (2000). They found, for the UK during 1961 to 1995, more heavy rainfall in winter compared to light and medium rainfall, while the opposite happened in the summer.
  • The area around Achnashellach in Wester Ross has the largest change, with a reduction of up to 10 days in spring, summer and autumn.

Future trends


  • The UKCIP02 report does not give any estimates for this measure.

Figure 33 - Patterns of change in the number of days with heavy rain (equal to or more than 10 millimetres) between 1961 and 2004 for each season.