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How were the aggregated areas decided on and implemented?
The aggregated areas used were informed by consultations with the UKCP09 Users' panel and decided on by the Steering Group.
The actual assignment of individual grid squares to aggregated areas
was based on the proportion of each UKCP09 25 km grid square in each
area.
In detail
The probabilistic nature of the UKCP09 climate projections means that it is not possible to simply average projections from neighbouring 25 km grid squares to get a result. Instead, projections were additionally calculated for a limited number of pre-defined aggregated areas.
Finite computer resources imposed a limit on the number of pre-defined
aggregated areas that could be prepared. With this in mind, the UKCP09 Users' panel were consulted to establish the most useful ways of
dividing up land areas of the UK. The two most commonly requested
aggregated areas were administrative regions (specifially the nine English government office regions and the 3 devolved administrations) and river basins (specifically the Water Framework Directive River Basins Districts).
In both cases, the large geographic area of Scotland was further
sub-divided. For administrative regions, the Met Office climatic
districts were used to sub-divide Scotland into three smaller regions.
For river basins, the single large Scotland RBD was sub-divided into 10
smaller Advisory Group areas.
The implementation of the aggregated areas involved
assigning each UKCP09 25 km grid square to an aggregated area. A
weighting approach was used (again following consultation of the UKCP09
users' panel), whereby GIS software was to calculate the proportion of
each 25 km grid square that fell in each aggregated area. This means
that each 25 km grid square may have contributed towards two or more
aggregared areas.
For marine regions,
the Marine Climate Change Impacts Partnership (MCCIP) suggested the use
of the Regional Reporting Areas used in Defra's Charting Progress study
(2005). These were modified to cover the UKCP09 25 km grid extent and
to add an additional area to the west of Ireland, and consequently
renamed as UKCP09 marine regions. Furthermore, a simpler assignment
approach was used, whereby each 25 km grid square was assigned to one
marine region (i.e. no weighting based on area covered).
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