Examining the Eastern European heatwave of 2023 from a long-term perspective: the role of natural variability vs. anthropogenic factors

Abstract. Amidst unprecedent rising global temperatures, this study investigates the historical context of heatwave (HW) events in Eastern Europe. The record-breaking 2023 summer, featuring a heatwave lasting for 19 days in the south-eastern part of Romania, extending up to Ukraine, necessitates a deeper understanding of past extreme events. Utilizing statistical methods on long-term station data spanning from 1885 to 2023, we aim to detect and analyze historical heatwaves, particularly focusing on events predating 1960. This extended timeframe allows for a more comprehensive assessment of noteworthy extremes compared to recent decades. Our analysis identifies two critical periods with increased heatwave frequency and intensity: 1920–1965 and 1980–2023, respectively, highlighting the most extreme events in August 1946, August 1952, July 2012, June 2019, and August 2023. Furthermore, reanalysis data shows that historical heatwaves, similar to the 2023 event, were associated with large-scale European heat extremes linked to high-pressure systems and they were accompanied by extreme drought, thus leading to compound extreme events. We find that while a clear trend emerges towards more frequent HWs from the 1980s onward, the analysis also uncovers substantial heatwave activity on daily timescales throughout the 1885–1960 period. Moreover, we highlight the intertwined impacts of climate change and multidecadal internal variability on heatwave patterns, with evidence suggesting that both contribute to the increasing frequency and intensity of these extreme events. Our research highlights the value of extending the historical record for a more nuanced understanding of heatwave behavior and suggests that extreme heat events, comparable to those experienced in recent decades, have occurred throughout the analyzed period.