Linking European droughts to large-scale atmospheric circulation

Droughts are among the most impactful climate-related hazards in Europe, with severe consequences for agriculture, ecosystems, water resources, and energy production. Despite their importance, the meteorological precursors and drivers of droughts remain difficult to anticipate due to their complex link with atmospheric circulation variability. This study investigates how large-scale North-Atlantic weather regimes (WR) influence the spatial and temporal characteristics of meteorological droughts across Europe, throughout the entire annual cycle.

Using ERA5 reanalysis data from 1960 to 2023 and the Standardized Precipitation Index (SPI) at a three-month timescale, we examine the statistical relationships between WR frequency and the occurence of drought events across different areas of Europe. These areas result from a regionalization strategy consisting in aggregating adjacent grid cells according to the concurrence of dry spells. We compute year-round WR from anomalies of geopotential height at 500 hPa. Each WR is found to be associated with a mean precipitation anomaly pattern across Europe that exhibits a relatively weak seasonality.

Our results reveal that, for each considered region, the 90-day periods preceding the peak of drought events are characterized by a significantly anomalous occurrence of some WRs, with respect to their climatological frequency. We can thus recontruct a precipitation signal by using these frequency anomalies as weights to compute a weighted mean of the precipitation pattern maps associated to the relevant WR. The reconstructed precipitation signal is consistent with the precipitation anomaly pattern from drought composites, albeit with a weaker amplitude. We then characterize the situations for which WR frequency anomaly substantially contributes to the developement of meteorological droughts. Our results also highlight regional contrasts, suggesting that drought early-warning systems could benefit from tailored WR-based indicators.

Overall, these findings underscore the relevance of WRs as a physically interpretable framework to monitor and anticipate drought risk at sub-seasonal to seasonal timescales. Integrating regime diagnostics into operational monitoring could enhance the preparedness and responsiveness to drought episodes under both current and future climate conditions.