Heatwaves were defined as minimum temperature exceeding the 99th percentile of minimum temperature for the reference period (1986-2005) for four or more days. From this definition, four heatwave indicators are derived: Number of heatwave instances Total number of days of heatwave Heatwave degree-days over threshold, being the sum of the differences between the daily temperatures and the 99th percentile threshold Mean length of heatwaves Heatwave  mean degrees over threshold, being the heatwave degree-days divided by the total number of days.   These definitions were applied to ECMWF ERA5 temperature data at 0.5˚ grid resolution for the years 1980-2018. Each indicator is provided in a separate file.