Regional nudged storylines for the European hot and dry summers 2018–2022: response of evapotranspiration regimes to climate change

Europe has recently experienced a series of hot and dry summers. Previous case studies indicate that, for a given atmospheric circulation, heatwave temperatures may increase by 1.5–3 K per degree of global warming, but the magnitude of this amplification varies substantially across regions and events, and its underlying mechanisms remain insufficiently constrained. Here, we investigate this variability using circulation-nudged regional climate storylines for the summers 2018–2022, dynamically downscaled over Europe and spanning climates from pre-industrial conditions to +4 K global warming. The present-day simulations realistically reproduce observed temperature, soil moisture, and surface fluxes. We find that warming amplification is spatially heterogeneous and seasonally dependent, with the strongest amplification over Central Europe occurring in August, indicating a disproportionate intensification of late-summer heatwaves. Using the evaporative fraction-soil moisture framework, we show that warming amplification is closely linked to changes in the evapotranspiration regime. The strongest amplification occurs when warming induces a transition from energy-limited to moisture-limited conditions, triggering rapid soil moisture depletion, a pronounced reduction in evaporative fraction, and enhanced sensible heating. ... mehrIn contrast, amplification is weaker when conditions are already moisture-limited in the pre-industrial climate, due to the reduced potential for further soil drying, and weakest when the regime remains energy-limited. These findings demonstrate that spatial and event-to-event differences in warming amplification can partially be attributed to the sensitivity of land-atmosphere coupling to soil moisture changes. Accounting for these feedbacks is essential for robust projections of future heat extremes and for identifying regions most vulnerable to disproportionate increases in heatwave intensity.