The 2021 European Heat Wave in the Context of Past Major Heat Waves

The past two decades in Europe have been characterized by numerous major heat waves, with record-breaking temperatures reported also during the summer of 2021. While most previous studies on heat waves were based on land-only datasets (station or gridded), we use the ERA5 reanalysis to capture also heat wave characteristics over water bodies. An up-to-date list of major European heat waves since 1950 is presented, and the 2021 heat wave is evaluated in this long-term context. This event was record-breaking in length at the European scale, and in many other aspects (spatial extent, magnitude) comparable to the 2003 and 2010 major heat waves. The summer of 2021 was unprecedented over Europe according to the number of hot days (63) and the earliest start of a major heat wave (June 19), while the 2019 heat wave with record-breaking temperatures across Western Europe stands out as to its intensity. Another recent major heat wave in 2018 ranked fourth in terms of magnitude. The spatial pattern in occurrence of the most severe heat wave since 1950 in individual parts of Europe is dominated by the 2003 (Western Europe), 2010 (Eastern Europe), 2018 (Scandinavia), and 2021 (Mediterranean) major heat waves. Overall, 83% of the domain area experienced the most severe heat wave in the past two decades (2002-2021), which demonstrates a rapidly changing summer climate in Europe. Plain Language Summary Heat waves, characterized as several days to weeks long periods with excessively hot weather in summer, have negative effects on environment and society. The severity of heat waves has increased in the past two decades and record-breaking temperatures were observed during the recent summer of 2021 over the Mediterranean. We used the climate reanalysis (ERA5) to create an up-to-date list of major European heat waves since 1950 and assess the severity of the 2021 heat wave in the long-term context. The 2021 heat wave was found to be comparable to the 2003 and 2010 major heat waves in terms of magnitude and spatial extent and record-breaking in length. Maps depicting the record-breaking heat waves over European regions differ substantially between the 1950-2001 and 1950-2021 periods. The latter map is dominated by the 2003, 2010, 2018, and 2021 heat waves, demonstrating a rapidly changing summer climate in Europe.

Automated summary

The past two decades in Europe have experienced numerous major heat waves, with the summers of 2019 and 2021 standing out as record-breaking events. The 2021 heat wave in particular set a new record in terms of its duration across Europe. The study also reveals the rapid changing summer climate in Europe.