Chapter 9: Road drainage and the water environment

3.8 Climate Change
The impacts of climate change are uncertain. Modelling carried out by the Hadley
Centre (Met Office) has looked at a number of different scenarios. These models
suggest that winters will become wetter over the whole of the UK, by as much as
20 per cent by the 2050’s.
A shift in the seasonal pattern of rainfall is also expected, with summer and
autumn becoming much drier than at present. However, the intensity of the
rainfall during summer storms is predicted to be much greater. So even though
the overall amount of rain in the summer will be less, there will be more
occurrences of heavy rainfall.
Once constructed, the development is expected to be there for at least 100 years.
(This is generally considered an appropriate time horizon for Developers to have
to accommodate.)
However, once an area has become developed, it is more likely to remain
developed in some form or another beyond this life-span. This should be taken
into account in longer-term strategies for the area.
Therefore, climate change will present a Future Risk to the site in the form of
greater volumes of surface water runoff from the surrounding area and from the
site itself.
In making an assessment of the impacts of climate change Table 5 shows the
precautionary allowances that should be considered for the parameters relevant
to this site.
Parameter
1990 to
2025
2025 to
2055
2055 to
2085
2085 to
2115
Peak rainfall intensity +5% +10% +20% +30%
Peak river flow +10% +20%
Table 5: Recommended national precautionary sensitivity ranges 4
4 PPS25 – Table B2
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