How the HadUK-Grid climate datasets have been produced.
The gridded data sets are based on the archive of UK weather observations held at the Met Office. The density of the station network used varies through time, and for different climate variables — for example, for the temperature variables the number of stations rises from about 270 in the 1910s to 600 in the mid-1990s, before falling to 450 in 2006.
Regression and interpolation are used to generate values on a regular grid from the irregular station network, taking into account factors such as latitude and longitude, altitude and terrain shape, coastal influence, and urban land use. This alleviates the impact of station openings and closures on homogeneity, but the impacts of a changing station network cannot be removed entirely, especially in areas of complex topography or sparse station coverage. The methods used to generate the monthly and annual grids are described in more detail in a paper published in the International Journal of Climatology, vol. 25 (2005), pages 1,041-1,054, which can be downloaded here: Generation of monthly gridded data sets for a range of climatic variables over the UK (PDF, 590 kB). The methods used to generate the daily grids are described in more detail in the report 'The generation of the daily gridded data sets of temperature and rainfall for the UK' (PDF, 2.27 MB).
The 1 × 1 km grids of the 1981-2000 baseline climate average have been provided for use alongside other products from the UKCP18 project . These averages are simply calculated by averaging or summing the 30 monthly or annual gridded data sets for each variable. The methods used to generate the1 × 1 km data sets for 30-year average periods 1961-1990 and 1981-2010 are described in a paper published in the International Journal of Climatology, vol. 25 (2005), pages 1,023-1,039, which can be downloaded here: Development of a new set of long-term averages for the UK
(PDF, 1.08 MB)
To help users combine the baseline data sets with the UK Climate Projections, values have also been generated for the 12, 15, and 60 km projection resolutions and for countries, administrative regions and river basins.
Each coarser resolution grid box value is an average of the 1 × 1 km grid cell values that fall within it. Averages have been calculated for each month, season and the year as a whole. Each regional value is also an average of the 1 × 1 km grid cell values that fall within the specificed geographical region.
The improvements and developments compared to previous UK gridded climate dataset are summarised in the overview pages.