Many indices have been defined to estimate the intensity of a heatwave. However, these indices are often used indiscriminately, without sufficient consideration of their possible different results and of the challenges that this poses to a proper characterization and comparison of events.
This study, by comparing four different indices applied to reanalyses data, shows that the choice of heatwave intensity metrics has important effects on the detection of the most intense events for the period 1950-2021, with indices based on cumulative values of a target variable that must be preferred over the ones relying on temporal averages. Under these considerations, one of the given indices is additionally selected for the study of heatwaves of the period 1950-2021, showing that heatwaves that were unlikely before 1986 have become up to ten times more usual and up to three times more intense during recent times.