Temperature related variables

Length of heat-waves in summer and cold spells in winter


Figure 20 - a) Length of summer heat-waves (in days) and b) length of winter cold spells (in days) for Scottish regions, from 1961 to 2003, with smoothed curves showing a running average.

Table 11 - Change in half-year heat-wave and cold spells (in days), from 1961 to 2003. 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
Heat-wave (summer) 6.3 6.3 4.3 5.7
Cold spell (winter) -5.8 -8.4 -8.9 -7.5


Please note, in calculating heat-waves summer is taken as a half-year season from April to September, cold spells are calculated for the October to March winter half-year.


Regional trends

  • We can see an increase in the length of summer heat-waves between 1961 and 2003 in all regions throughout the year but the change is not part of a measurable trend and so it may be a result of natural variability
  • The only trend we have identified is the reduction in the length of cold spells during the winter half-year in East and West Scotland.


Spatial trends

  • Cold spells in winter have reduced most in southern Scotland and the Shetlands, a pattern that correlates well with the pattern of winter temperature changes.
  • Summer heat-waves have got longer in areas furthest away from the coast and in north-eastern areas.


Future trends

  • There is no assessment in the UKCIP02 scenarios report of future changes to the length of heat-waves or cold spells.


Figure 21 - Pattern of change in the length of a) winter half-year cold spells (in days, left-hand panel) and b) summer half-year heat-waves (in days, right-hand panel), from 1961 to 2003.