Large-scale causal drivers of European winter precipitation

Abstract Large-scale atmospheric dynamics drive a substantial share of winter precipitation in the Euro-Atlantic sector. Still, the associated mechanisms remain only partially understood despite their relevance for seasonal forecasting and climate predictions and projections. While averaged modes like the North Atlantic Oscillation (NAO) prove useful in regressing precipitation, in this study we aim to add a layer of physical interpretability and disentangle individual mechanisms that affect precipitation. Using a causal discovery framework applied independently at every grid point across the Euro-Atlantic domain, we identify direct large-scale drivers of winter precipitation locally, with dependencies found to be predominantly linear and contemporaneous at monthly timescales. Causal links are uncovered, including a direct connection between Barents--Kara sea ice and Iberian Peninsula precipitation, together with evidence that the stratospheric polar vortex causally associates with precipitation across northern and southern Europe without requiring other large-scale intermediaries. Unsupervised clustering of the identified causal structure organises local precipitation into coherent regions resolving most of the Euro-Atlantic domain. Using the identified causal drivers, a multiple linear regression framework on precipitation achieves significant explanatory power over a substantially larger fraction of the domain than the NAO, and regionally outperforms it in explained variance away from its centres of action, showing that a physically grounded understanding of the mechanisms driving precipitation also yields a better description of it.