When hot nights will not allow to relax: Projections of co-occurring extreme heat events over Central Europe under policy-relevant global warming levels

Co-occurring warm days and warm nights can generate sustained heat stress and reduce nighttime recovery, increasing risks to health and socio-economic systems. We assess how such co-occurring heat extremes are projected to evolve over Central Europe using the Global Warming Level (GWL) framework. To strengthen decision relevance, we evaluate Paris Agreement targets (1.5 °C and 2.0 °C) together with policy-relevant warming levels linked to current pledges and policies (1.9 °C and 2.7 °C). Projections are derived from two performance-informed sub-ensembles of CMIP6 climate simulations and are analysed spatially and for selected NUTS administrative regions, aligning results with adaptation planning. NUTS-level outputs for six Central European countries are available via Zenodo. Co-occurrence events analysed in this study were rare during the observational period (1995–2014) over most of the domain, with localised hotspots in warmer lowland areas. Across the analysed GWLs, co-occurring heat extremes become more widespread and frequent across Central Europe. The transition from GWL1.5 to GWL1.9 is characterised by a broad emergence of co-occurrences, whereas the largest increases in spatial extent and intensity occur between GWL2.0 and GWL2.7. Hungary and Slovakia consistently show the highest projected frequencies, the longest event durations, and the greatest expansion of affected areas, indicating elevated heat risk. Uncertainty is dominated by model differences; scenario effects are generally smaller but increase at higher warming levels. Overall, comparing Paris Agreement and policy-relevant warming levels reveals substantial regional differences, with Hungarian and Slovak NUTS regions exhibiting the strongest projected responses, highlighting the importance of regional adaptation planning.