Scottish Road Network Climate Change Study: UKCP09 update Autumn 2011

5 Temperature related variables

Temperature is one of the underlying parameters that affects a number of areas of road design and operation. The conditions in which road surfacing materials may be laid and concrete placed are dependent on temperature and the expected long-term performance of these materials is based on the occurrence of a certain temperature environment. In addition, the growing season is temperature dependent and assumptions relating to the need for maintenance of landscaping areas are also based on the occurrence of a certain temperature environment.

How to use the tables

5.1 Annual mean temperature

Table 5.1 provides the projected changes by the 2080s to mean annual temperature for the three target locations. Figures 5.1 to 5.3 provide Scotland-wide changes for the 2080s medium emission scenario for each of the 10, 50 and 90 percentile probabilities.

Table 5.1 - Change in annual mean temperature compared to the 1961-1990 baseline period for different emission scenarios (in oC).
Emission scenario Glasgow Aviemore Dundee
High 2080s +3.8
[ +2.5 to +5.6]		 +3.5
[ +2.2 to +5.2 ]		 +3.4
[ +2.2 to +5.1]
Medium 2080s +3.1
[+2.0 to +4.6]		 +2.9
[ +1.8 to +4.3 ]		 +2.8
[ +1.7 to +4.3 ]
Low 2080s +2.5
[+1.5 to +3.8]		 +2.4
[ +1.4 to +3.7 ]		 +2.4
[ +1.4 to +3.6 ]

Figure 5.1 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (10 percentile).

Figure 5.1 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (10 percentile).

Figure 5.2 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (50 percentile).

Figure 5.2 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (50 percentile).

Figure 5.3 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (90 percentile).

Figure 5.3 - Change in Annual Mean temperature 2080s - Medium Emission Scenario (90 percentile).

5.2 Frost days

Table 5.2 provides the number of frost days derived from the Weather Generator data for the baseline and the 2080s medium emission scenario, together with the actual number obtained from observed data. The approximate estimates for Aviemore and Dundee are based on an interpolation of graphical information and should be treated with some caution. The Glasgow data is based on the analysis of the Paisley observed record which shows good correlation with the simulated baseline values of the Weather Generator.

Table 5.3 is as for Table 5.2 but provides the projected numbers for the 2020s medium emission scenario.

Table 5.2 - Number of frost days/year derived from the UKCP09 weather generator for the baseline and 2080s periods.
Site Observed Baseline 1961-1990 2080s Medium
10% 50% 90% 10% 50% 90%
Glasgow 42 41 43 45 5 14 24
Aviemore 100-120 129 132 135 40 66 87
Dundee 40-60 49 51 53 4 13 31

 

Table 5.3 - Number of frost days per year derived from the UKCP09 weather generator for the baseline and 2020s periods.
Site Observed Baseline 1961-1990 2020s Medium
10% 50% 90% 10% 50% 90%
Glasgow 42 41 43 45 17 23 32
Aviemore 100-120 129 132 135 75 96 111
Dundee 40-60 49 51 53 22 30 38

Tables 5.4 and 5.5 present the reduction in the number of frost days under different scenarios. (Refer to the Box at the start of this chapter for an explanation of values in bold and in the brackets. Also refer to section 4.2). These tables indicate that the reduction in the number of frost days is likely to be highest in the near future compared to near the end of the 21st century. This is to be expected, since as the temperatures warm up, the number of frost days will tend towards zero as the probability function of minimum temperatures (which will have the characteristics of a bell shaped function) is effectively shifted to warmer temperatures.

Table 5.4 - Reduction in the number of days per year of frost by the 2080s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2080s -33
[-24 to -39]		 -74
[-46 to -101]		 -42
[-26 to -54]
Medium 2080s -31
[-19 to -38]		 -67
[-44 to -92]		 -38
[-19 to -49]
Low 2080s -30
[-23 to -37]		 -55
[-29 to -77]		 -30
[-20 to -40]

 

Table 5.5 - Reduction in the number of days per year of frost by the 2020s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2020s -21
[-12 to -27]		 -34
[-17 to -53]		 -20
[-10 to -28]
Medium 2020s -20
[-10 to -27]		 -37
[-22 to -55]		 -21
[-13 to -29]
Low 2020s -20
[-10 to -27]		 -33
[-16 to -48]		 -21
[-11 to -31]

Figure 5.4 presents the Scotland-wide pattern of projections for how the number of frost days are likely to change between the 1961-1990 baseline period to the 2080s.

Figure 5.4 - Number of frost days annually estimated by the Weather Generator for the baseline period 1961 - 1990 (top row) and for the 2080s medium emissions projections (bottom row). [Source: Jones PD et al (2009)].

Figure 5.4 - Number of frost days annually estimated by the Weather Generator for the baseline period 1961 - 1990 (top row) and for the 2080s medium emissions projections (bottom row). [Source: Jones PD et al (2009)].

Comparison to estimates derived from UKCIP02 projections:
The above UKCP09 projections are based on the analysis of whole years and are not directly comparable to the earlier work that was undertaken on only on a 90-day winter period (December - February).

The UKCIP02 based study suggested that by the 2080s that there would be a 33% reduction in the number of frost days during the period December - February in Aviemore and a 50% reduction in Glasgow.

This UKCP09 based study suggests that by the 2080s there would be a 50% reduction in the number of frost days per year in Aviemore and a 66% reduction in Glasgow.

5.3 Freeze - Thaw

This variable was not studied in the earlier report based on the UKCIP02 scenarios. Tables 5.6 and 5.7 provide the average number of freeze-thaw events derived from the Weather Generator data for the baseline and the 2080s and 2020s medium emission scenarios. In addition in the case of Glasgow the actual number obtained from observed data is also included for comparison with the simulated 1961-1990 baseline.

Table 5.6 - Number of freeze-thaw days per year derived from the UKCP09 Weather Generator for the baseline and 2080s periods.
Site Observed Baseline 1961-1990 2080s Medium
10% 50% 90% 10% 50% 90%
Glasgow 38.1 35 38 70 3 13 25
Aviemore (na) 98 108 206 35 77 117
Dundee (na) 44 51 95 10 22 51

 

Table 5.7 - Number of freeze thaw days per year derived from the UKCP09 Weather Generator for the baseline and 2020s periods.
Site Observed Baseline 1961-1990 2020s Medium
10% 50% 90% 10% 50% 90%
Glasgow 38.1 35 38 70 13 22 38
Aviemore (na) 98 108 206 70 86 158
Dundee (na) 44 51 95 19 29 51

Table 5.8 presents the projected reduction in the number of freeze-thaw days under different scenarios.

Table 5.8 - Reduction in the number of freeze-thaw days per year of frost by the 2080s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2080s -26
[-13 to -48]		 -33
[-8 to -51]		 -30
[-7 to -49]
Medium 2080s -25
[-14 to -47]		 -33
[-9 to -50]		 -29
[-6 to -44]
Low 2080s -22
[-15 to -45]		 -29
[-10 to -44]		 -27
[-6 to -42]

5.4 Winter duration

Figures 5.5 a) - c) graphically indicate how the present allocated winter period (1 October to 15 May) is likely to reduce at the three example sites. For the 2080s medium scenario the predictions suggest a 45 day reduction in the winter period for both Glasgow and Aviemore. However for Dundee, the decrease is predicted to be a bit larger at 65 days.

Figure 5.5 a) - Glasgow: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

Figure 5.5 a) - Glasgow: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

Figure 5.5 b) - Dundee: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

Figure 5.5 b) - Dundee: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

Figure 5.5 c) - Aviemore: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

Figure 5.5 c) - Aviemore: projected change in the winter duration, 2080s medium emission scenario (change indicated by black dotted line).

5.5 Hot days

Tables 5.9 and 5.10 provide the average number of days per year when top temperatures reached > 25 oC. Baseline and 2080s medium emissions scenario values have been derived from the analysis of Weather Generator. Also shown for Glasgow is the actual number obtained from observed data.

Table 5.9 - Number of days per year with maximum temperature greater than 25 oC derived from the UKCP09 Weather Generator for the baseline and 2080s periods.
Site Observed Baseline 1961-1990 2080s Medium
10% 50% 90% 10% 50% 90%
Glasgow 4.5 0.9 1.2 1.5 6.2 16.8 38.9
Aviemore (na) 0.0 0.1 0.2 1.5 4.1 20.8
Dundee (na) 0.4 0.6 0.8 3.7 14.4 34.9

 

Table 5.10 - Number of days per year with maximum temperature greater than 25 oC derived from the UKCP09 Weather Generator for the baseline and 2020s periods.
Site Observed Baseline 1961-1990 2020s Medium
10% 50% 90% 10% 50% 90%
Glasgow 4.5 0.9 1.3 1.7 1.9 3.7 8.9
Aviemore (na) 0.0 0.1 0.3 0.3 0.7 1.9
Dundee (na) 0.7 0.9 1.2 1.4 3.5 7.3

Tables 5.11 and 5.12 present the increase in the number of days exceeding 25 oC under different scenarios.

Table 5.11 - Increase in the number of days per year with maximum temperature greater than 25 oC by the 2080s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2080s +20
[+8 to +60]		 +8
[+2 to +23]		 +24
[+6 to +56]
Medium 2080s +15
[+5 to +38]		 +4
[+1 to +21]		 +14
[+3 to +34]
Low 2080s +9
[+3 to +25]		 +3
[+0 to +10]		 +10
[+2 to +25]

 

Table 5.12 - Increase in the number of days per year with maximum temperature greater than 25 oC by the 2020s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2020s +3
[+1 to +6]		 +1
[0 to +2]		 +3
[+1 to +6]
Medium 2020s +2
[+1 to +8]		 +1
[0 to +2]		 +3
[+1 to +6]
Low 2020s +3
[+1 to +7]		 +1
[0 to +2]		 +2
[+1 to +6]

Maps of the change in high temperature days (>25 oC ) are found in Figure 5.6.

Figure 5.6 - Number of days per year with maximum temperature greater than 25 oC estimated by the Weather Generator for the baseline period 1961 - 1990 (top row) and for the 2080s medium emissions projections (bottom row). [Source: Jones PD et al (2009)].

Figure 5.6 - Number of days per year with maximum temperature greater than 25 oC estimated by the Weather Generator for the baseline period 1961 - 1990 (top row) and for the 2080s medium emissions projections (bottom row). [Source: Jones PD et al (2009)].

Table 5.13 provides the average number of days per year when top temperatures reached > 30 oC. Baseline and 2080s medium emissions scenario values have been derived from the analysis of Weather Generator. Also shown for Glasgow is the actual number obtained from observed data.

Table 5.13 - Number of days per year with maximum temperature greater than 30 oC derived from the UKCP09 Weather Generator for the baseline and 2080s periods.
Site Observed Baseline 1961-1990 2080s Medium
10% 50% 90% 10% 50% 90%
Glasgow 0.02 -0.1 0 0.3 -3 0.1 3
Aviemore (na) -0.2 0 0.2 0 0.2 1.9
Dundee (na) -0.4 0 0.8 0 0.3 3

Table 5.14 presents the increase in the number of days exceeding 30 oC under different scenarios.

Table 5.14 - Increase in the number of days per year with maximum temperature greater than 30 oC by the 2080s compared to the 1961-1990 baseline period for different emission scenarios (in days).
Emission scenario Glasgow Aviemore Dundee
High 2080s +0.1
[-3 to +3]		 0
[-1 to +3]		 +0.3
[-2 to +4]
Medium 2080s +0.1
[-3 to +3]		 0
[-1 to +3]		 +0.3
[-2 to +3]
Low 2080s 0
[-2 to +2]		 0
[-1 to +2]		 +0.3
[-2 to +3]

Comparison to estimates derived from UKCIP02 projections:

In the earlier work the number of occurrences of >30 oC was not quantified at either Glasgow or Aviemore. However the indications were that there would be a slight increase by the 2080s and that even higher temperatures may on occasion be experienced.

5.6 Growing season

(The findings of this analysis presented unexpected results for the baseline condition which did not agree with previously published values. At the time of writing this report the issue has been raised with the UKCP09 technical team and the situation has yet to be resolved).

According to the information provided in the SNIFFER trends report[4], over Scotland as a whole the growing season has lengthened since the early 1960s by on average 33 days with about 21 days of this coming from an earlier commencement of the growing season and 12 days extension of the growing season at the end of the year. Slightly larger changes have been experienced in the west and slightly smaller changes in the north.

These changes are slightly higher than the upper bound of those presented in the earlier Scottish Road Network Climate Change study which pointed towards an increase of 22 +/- 10 days by the 2020s from the 1961-90 baseline period. Little should be read into the higher observed rate since natural decadal fluctuations are likely to exist and could be partially masking the long-term trend. However the recent increasing growing season is broadly in agreement with the projected changes given in the earlier Scottish Road Network Climate Change study.