Flaws are revealed in a highly cited database that dates back more than two centuries.

Scientists have identified biased data in an iconic meteorological record, and are now challenging conclusions about long-term precipitation trends in England, Wales and possibly other regions.

The England and Wales Precipitation (EWP) series is a continuous monthly record of British snow and rainfall, stretching back to 1766. For decades, climate scientists have used this record — one of the longest-running available — to examine precipitation and atmospheric-circulation patterns in northwest Europe.

Conor Murphy at Maynooth University, Ireland, and his colleagues drew on independent data, including long-term measurements of British snowfall, to reconstruct the record’s early portion. Their reconstruction showed that the EWP underestimated winter precipitation before 1870, whereas summer rainfall was overestimated before 1820. As a result, the widely accepted conclusion that winters have become wetter and summers dryer since 1766 appears to be an artefact.

Scientists should exercise caution in using early EWP data and when drawing conclusions from other multicentury precipitation datasets, the authors say.