Recent European drying and its link to prevailing large-scale atmospheric patterns

The European continent has been struck by several extreme droughts over the last decades, associated with wide ranging societal, environmental and economic impacts. Changes in large-scale atmospheric circulation are vital for understanding the spatial patterns of changes in seasonal meteorological drought. The study presented herein is based on Bakke et al. (in review) and we begin by demonstrating the coherent pattern in the development of extreme meteorological drought and high-pressure systems during the extreme 2018 and 2022 drought events in Europe. Next, we investigate the relation between changes in large-scale atmospheric patterns and meteorological drought, as indicated by the geopotential height at 500mb (Z500) and the Standardised Precipitation-Evapotranspiration Index (SPEI), respectively. Calculations are done separately for four climate regions (North, West, Central-East and Mediterranean) over the growing season (March-September). Overall, the results show a low sensitivity to the Z500 data sets used (NCEP, ERA5, ERA20C and 20C), and the SPEI data sets (CRU and EOBS) at the regional level. We find coherent spatial patterns in 1979–2021 trends in seasonal and monthly Z500 and SPEI, with hot spots of significant changes towards higher pressure (increasing Z500) and drier conditions (decreasing SPEI) over West in spring and Central-East in summer. Strong correlations (at 1% significance level) between the variables are found for all regions throughout the growing season. A strong relation between high-pressure systems and meteorological drought is confirmed by a high degree of co-occurring regional anomalies since the beginning of the 20th century. The strongest links are detected in West, and the weakest links in North. Finally, we investigate projected Z500 according to a low-end (SSP126) and a high-end (SSP585) emission scenario. According to the projected changes, anomalously high-pressure systems will be the new normal regardless of scenario, and well exceeding the 2018 and 2022 levels in the case of the high-end emission scenario. The ability of the model ensemble to represent the spatial heterogeneity in historical Z500 variability and trends is limited. Thus, projected changes in large-scale circulation are highly uncertain. Consequently, due to the strong link between Z500 and SPEI, high uncertainties are associated with projected changes in drying trends and meteorological drought across Europe.

Bakke, S.J., Ionita, M. and Tallaksen, L.M.: Recent European drying and its link to prevailing large-scale atmospheric patterns. npj Climate and Atmospheric Science (in review). https://doi.org/10.21203/rs.3.rs-2397739/v1