The influence of anthropogenic warming on Storm Gloria: a km-scale storyline approach

We present a physical storylines study of storm Gloria, a devastating extra-tropical cyclone in January 2020 over the western Mediterranean that caused record-breaking precipitation, fatalities, and millions in damages. The study is performed using the global, coupled, km-scale IFS-FESOM model, developed under the European Union’s Destination Earth initiative. We run the model using spectral nudging, where the upper atmosphere is nudged hourly with ERA5 reanalysis to recreate the observed weather patterns in a Counterfactual (cooler, ~1950’s), Actual (~2020) and Future (warmer, ~2040’s) background climate. The ~9 km, hourly resolution allows us to analyze localized extreme precipitation at scales useful for adaptation planning. 

The work will be presented in two parts. In the first section we will present a novel probabilistic attribution study using the climatology of the storyline simulations, quantifying the changes in probability of key atmospheric variables observed during Gloria in a warmer climate. This is made possible due to the continuous 7-year runs of the global storyline simulations, allowing us to build DJF climatologies for the three different climate scenarios. We find that all atmospheric variables show statistically significant increases, with Gloria-level precipitable water over twice as likely to occur in the Future climate scenario. 

In the second part we present an in-depth comparison of the event under different climates, both in terms of atmospheric drivers and hydrologic impacts analyzed via a runoff model. We find that while precipitable water and integrated vapor transport follow Clausius-Clapeyron scaling, extreme precipitation shifts locally, increasing up to 45% in some areas but not always translating to higher runoff due to drier soils. Though focused on storm Gloria, we emphasize the global nature of these simulations and their contribution to equitable access to climate adaptation information in the analysis of extreme events. Indeed, we refer to the abstract by Campos D, “Attribution of the synoptic-scale meteorological conditions associated with the October 2024 DANA event over Valencia, Spain” who uses the same simulations to understand the impacts of warming of the recent DANA event over Valencia.