Future Patterns of Compound Dry and Hot Summers and Their Link to Soil Moisture Droughts in Europe

Abstract

Compound dry and hot extreme (CDHE) summers in Europe, like 2015, 2018 and 2022, have wide ranging impacts: heat exacerbates moisture shortages during dry periods whereas water demand rises. Current studies of CDHE are mostly conducted in observations or coarse-resolution global climate model large ensembles. While the latter allow for the assessment of rare CDHE against the backdrop of internal variability, global ensembles fail in providing robust climate change signals at impact-relevant scales. To overcome this issue, we exploit a regional 50-member single-model initial condition large ensemble (SMILE). The SMILE provides an extensive database of CDHE in a current climate and at two global warming levels (+2°C, +3°C) across Europe in high geographical detail. We identify Northern France, Southern Germany, Switzerland, Southern Ireland, and the western coasts of the Black Sea with currently low CDHE frequency as emerging hotspots. These regions experience a tenfold increase of CDHE under global warming conditions, in parts resulting in yet unseen heat and dryness. Temperature is the dominant driver of frequency increases, except for western Europe. Additionally, tail dependence strengthens in regions with large increases in CDHE frequency. In European agricultural areas, soil moisture shows stronger negative correlations with CDHE intensity than with precipitation or temperature. Finally, our results indicate $50\%$ fewer CDHE summers in a +2°C world compared to a +3°C world, highlighting the importance of climate mitigation to reduce the frequency of these multi-hazard events.