Reconstructing storm Gloria in a changing climate using physical storylines

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We present a storyline analysis investigating the impacts of background warming on storm Gloria, a severe winter storm that affected the western Mediterranean in January 2020, producing exceptional precipitation, fatalities, and substantial economic damage. The study employs global, ~ 9 km, IFS-FESOM simulations, constrained with spectral nudging to reproduce large-scale conditions under Counterfactual, Actual, and Future climates between 2017 and 2024. The plausibility of the simulated climates is assessed by comparing relative changes in seven-year DJF distributions of precipitable water (PW), integrated vapour transport (IVT) and precipitation between the Counterfactual and Actual simulations against corresponding Past and Present periods in ERA5. The close agreement indicates that the simulated thermodynamic differences are consistent with reanalysis-based differences. We then examine Gloria’s evolution across the three climates. PW and IVT increase with warming rates close to Clausius-Clapeyron scaling. In contrast, precipitation show strong spatial heterogeneity and differences deviate from thermodynamic scaling due to changes in the persistence and organisation of vertical motion. Despite local variability, total event-integrated precipitation increases by 6.3% from the Counterfactual to the Future climate. These findings illustrate the strengths and limitations of spectrally-nudged storylines for dynamically complex storms and their value in separating thermodynamic amplification from dynamical modulation.

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