GHCN-Daily: a treasure trove of climate data awaiting discovery.

International collaboration to create and maintain international, freely accessible datasets greatly facilitates research in many scientific fields. The Global Historical Climatology Network (GHCN)-Daily database provides access to a diverse range of daily weather station data, including precipitation and temperature variables. These data are supplied as individual, station-specific files and structured in a non-delimited format. Here, the GHCN-Daily data structure, spatio-temporal content and associated caveats are delineated. The regularly updated collection now features data from over 100 000 stations in 218 countries and territories. While rigorous quality tests are routinely applied for GHCN-Daily, the database excludes the original quality flags from the source agencies.