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EXECUTIVE SUMMARY
Following a number of landslide events in the summer of
2004, Nicol Stephen
MSP, Minister for Transport,
commissioned two studies to consider issues arising from
these events. The first study focused on landslide risks
and how they should be assessed, ranked and managed and is
reported elsewhere. This report presents the findings of
Study 2, which was to consider the potential trends in
climate change in Scotland and how these may affect the
road network. This study was undertaken by Jacobs Babtie,
supported by the Met Office.
The report outlines the historical information available
relating to severe weather events and how this is used in
the design and operation of the road network. The report
then assesses the implications of current climate change
predictions, including work commissioned specifically for
this study. This is to determine how the key weather
variables that impact on the road network, such as
temperature and rainfall, are predicted to change in the
future. These predictions have been based on modelled
climates for 30 year periods centred around the 2020's,
2050's and 2080's.
The general conclusion is that the climatic changes
expected in Scotland in the near future, as represented by
the 2020's, are relatively small. However, even these small
changes may be sufficiently significant to warrant
adjustment of current practices. While the report notes
that these changes are likely to become more marked over
the longer term, the degree of uncertainty associated with
these predictions increases. Consequently the
recommendations focus on responding to climatic changes
predicted to occur in the near future. These are presented
in terms of design, operation, further research or policy
review, as appropriate to the issue identified.
The findings in respect of predicted climate change
trends considered in this study are broadly as follows:
- Temperatures are expected to increase, resulting in
higher summer temperatures and fewer winter days when
freezing temperatures occur.
- Annual rainfall is expected to show little overall
change, however winter rainfall is expected to increase
and summer rainfall is expected to decrease.
- Snowfall days are expected to reduce.
- Wind speeds are expected to slightly increase,
however, this is an area of significant
uncertainty.
- Fog occurrence is expected to reduce, although this
is also an area of significant uncertainty.
- Coastal flooding levels are expected to increase,
particularly when storm surge is included within the
assessment.
One area of particular concern that has been identified
is the predicted increase in rainfall. It is considered
that in the near future this may result in drainage systems
failing to perform in the desired manner. To address this
concern, it is recommended that:
- The design storm parameters used in surface water
drainage design are revised to allow for predicted
increases.
- The design storm parameters used in culvert and
river bridge design are revised to allow for predicted
increases.
- Locations where flooding of the road network has
occurred are identified and potential solutions
evaluated on a cost/benefit basis, with priority for
those areas where repeated flooding occurs.
- Pre-emptive clearance of detritus from drainage
channels/watercourses is undertaken in known areas of
flooding risk, in response to predicted heavy
rainfall.
- Further research is undertaken in respect of the
parameters used in the estimation of catchment runoff.
This would enable guidance to be given on risk-based
design approaches, including evaluation of alternative
solutions on a cost/benefit basis.
In addition, recognising the opportunity afforded by the
proposed expansion of the Variable Message Sign (
VMS) network, and developing weather
prediction technology, it is recommended that:
- Consideration be given to using
VMS's to provide a greater level of
locally relevant information to road users on predicted
severe weather events, expressed in terms of
probability of occurrence.
Other recommendations are included in Section 6 of this
report for implementation in either the short or long-term
as appropriate to the issue concerned.
It is noted that actions are already in hand to address
some of the issues identified, such as the development of a
High Winds Strategy for the trunk road network. In
addition, agreement with other
UK road authorities is required to
address certain issues, for example where changes in design
standards are suggested.
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