Gridding uncertainties in UK climate data – progress and improvements

HadUK-Grid is a dataset of gridded in situ climate data for the UK. It comprises monthly, seasonal, annual and long-term average values for 11 variables at 1km resolution. Three of these variables are also available at daily resolution. It also contains area averages for the UK, constituent countries, administrative regions and river basins. The first version was released in 2018 and there have been annual updates since then. The latest version is v1.3.1.0 which includes data to the end of 2024.

In previous work we investigated the uncertainties in the gridded data using a leave-one-out cross-validation approach to calculate an RMS error. This gave a more detailed understanding of the characteristics of gridded UK climate data than had been available previously. However, it also highlighted several unexpected features as well as some deficiencies. These included: seasonal cycles and step changes in the RMSE for maximum temperature (that were not visible in minimum temperature), outliers in the RMSE time series caused by small numbers of poorly predicted stations, and pronounced trends in the RMSE for individual stations.

In this presentation we will give an update on progress towards understanding and, where appropriate, correcting these issues, including: an intercomparison of the results for different station types (coastal/inland, lowland/upland); an audit of which individual stations are having the most influence on the RMSE; an assessment of whether changes in exposure, equipment type or reporting practice might explain some of the observed trends or step changes; an investigation into ways to improve the gridding process in areas where the network is sparse, especially on the edge of the domain; and some thoughts on the relative importance of data quality, station density and gridding method.