Links between major heat waves, drought, and atmospheric circulation in Central Europe

Heat waves and drought are phenomena associated with large negative impacts on society and the environment. Their common features include increasing frequency and intensity in recent decades in many regions of Europe, as well as the interconnectedness of the factors that contribute to their development. In this study, we compare the long-term changes in the characteristics of major heat waves and severe drought in Central Europe (during the vegetation period (April-September)), examine the temporal and causal relationships between the two phenomena, their spatial and temporal scales, and the connection with atmospheric circulation. Based on E-OBS (daily temperature and precipitation) data since 1950 for the vegetation period (April-September), drought is characterized by the difference between potential evapotranspiration and precipitation, while heat waves are defined as periods of large positive anomalies of daily temperatures from the mean annual cycle affecting a large area. Heat waves occurring in early/late vegetation period are referred as warm spells due to their lower absolute temperatures and possibly different circulation mechanisms. We use the Jenkinson classification of daily sea level pressure fields from the NCEP/NCAR reanalysis to describe the atmospheric circulation. Circulation types with significantly increased frequency during periods of major heat waves/warm spells and droughts are identified, and changes in their occurrence are studied. We also focus on differences between the early (April-June) and late (July-September) parts of the vegetation period. The analysis contributes to a better understanding of the interrelationships between drought, heat waves, atmospheric circulation and other driving mechanisms during 1950–2019 in Central Europe.