Uncertainties in gridded area-average monthly temperature, precipitation and sunshine for the United Kingdom

We assess the uncertainties in the monthly 5-km resolution gridded values and derived areal averages of UK temperature and precipitation since 1910, and sunshine since 1929, developed by the Met Office National Climate Information Centre. Subsampling experiments are used to estimate the sampling uncertainties as a function of the density of the observing network; these estimates are then ascribed to historical gridded values and area averages according to the historical sampling density. Available historical manuscripts could support future extension of gridded and areal-average records back to 1901 for temperature, about 1871 for precipitation and 1921 for sunshine, with sufficient sampling to provide reliable historical context for current events. We combine the sampling uncertainties since 1910 with estimated calibration and measurement uncertainties to yield total uncertainties that we tabulate and illustrate in association with selected series. Methods and results are discussed in the light of existing estimates of uncertainties in Central England temperature and UK regional precipitation.