This dataset provides frequency and severity of heatwaves under past, current and future climate conditions which allows to estimate the thermal behavior of regions in Europe during episodes of extreme heat. A heatwave is typically defined as a “prolonged” period of “extremely high” temperature for a particular region or location. In REACHOUT, “prolonged” is defined by a period of two or more days and “extremely high” is determined per region when daily maximal temperature exceeds its threshold (95th percentile) and the daily minimum temperature exceeds its threshold (90th percentile). The percentiles were obtained considering the values of maximum and minimum temperatures of the region during the summer season of the baseline period of 1981 to 2010. To provide homogeneous data for the whole EU, the input variables used to generate this dataset come from the public, independent and authoritative Copernicus Climate Change Service (C3S). For the observations the e-OBS dataset is used and for the future projections the EURO-CORDEX dataset. The intermediate (RCP4.5) and very high (RCP8.5) emissions scenarios were considered. All the data was downloaded from the Copernicus Climate Data Store (CDS). The database is organized in three datasets: Regional_eobs_thresholds_Europe.csv: contains the thresholds that were used to detect the heatwaves for each region. They were calculated considering the values of maximum and minimum temperatures during the summer season of the baseline period (1981-2010). The columns are: region: unique identifier of the corresponding EUROSTAT NUTS_ID. tmax: daily maximum temperature threshold. tmin: daily minimum temperature threshold. Historical_eobs_heatwaves_Europe.csv: heatwaves of the historical period (1981-2021) for each region. The columns are: region: unique identifier of the corresponding EUROSTAT NUTS_ID. start: first date of the heatwave. tmax: maximum temperature reached during the heatwave. intensity: the sum of the degrees of the maximum and minimum temperatures over their corresponding thresholds. duration: duration of the heatwave. Future_and_baseline_eobs_heatwaves_Europe.csv: ensemble future projections of heatwaves. The columns are: hazard_level: it can be a warning, an alert or an alarm. region: unique identifier of the corresponding EUROSTAT NUTS_ID. experiment: emission scenario. It can be baseline, rcp-4-5 or rcp-8-5. period: it can be 1981-2010 for the baseline or 2011-2040, 2021-2050, 2031-2060, 2041-2070, 2051-2080, 2061-2090 or 2071-2100 for the future. decade_frequency: decade mean frequency. In the case of the future this is the ensemble of the models. decade_frequency_best: only applicable to the future. It determines the best projection among the models. decade_frequency_worst: only applicable to the future. It determines the worst projection among the models. year_days: average annual days. year_tmax_intensity: the average annual degrees of the maximum temperature over its corresponding threshold. year_tmin_intensity: the average annual degrees of the minimum temperature over its corresponding threshold.

We acknowledge the E-OBS dataset and the data providers in the ECA&D project ( https://www.ecad.eu). Cornes, R., G. van der Schrier, E.J.M. van den Besselaar, and P.D. Jones. 2018: An Ensemble Version of the E-OBS Temperature and Precipitation Datasets, J. Geophys. Res. Atmos., 123. doi:10.1029/2017JD028200