Causal Links Between El Niño–Southern Oscillation and European Compound Events: A Focus on False Spring Events

Extreme weather and climate events are increasingly linked to severe socio-economic impacts, and their combination in space and/or time can further amplify these effects. This has heightened attention on compound events, which are combinations of multiple, potentially non-extreme climate events that collectively result in significant socio-economic consequences. A prominent example of a compound event in agriculture are false spring event. These occur when anomalous warm and wet conditions prevail in late winter, triggering early crop growth, followed by spring frost or severe drought. Such conditions can lead to substantial agricultural losses. To enable early warnings for such events, seasonal predictability is essential, as these phenomena typically unfold over a period of a couple of months. Seasonal predictability typically stems from slowly varying factors, such as sea surface temperatures and teleconnections, which influence the likelihood and timing of such events.

 One of the most globally influential teleconnections is the El Niño–Southern Oscillation (ENSO), with well-documented influence on climate systems worldwide. ENSO's impact on European climate, particularly during late winter, has been extensively studied, raising the question whether ENSO could play a role in triggering false spring events. Investigating these mechanisms offers valuable insights into ENSO's influence on European climate and enhances the potential for improved seasonal predictions of such events. To identify these large-scale patterns and non-linear relationships with other teleconnection patterns and modes of variability, like the North Atlantic Oscillation (NAO), we employ advanced statistical techniques, such as Kernel Regularized Generalized Canonical Correlation Analysis and Bayesian neural networks. By leveraging preimages and Accumulated Local Effect (ALE) plots, we uncover large-scale mechanisms relevant to European climate that exhibit strong interactions with the Niño3.4 region. Finally, we perform a causal analysis to trace the chain of interactions and pathways through which ENSO modulates European false spring events. 

 Our preliminary analysis focused on the first phase of the compound events, late winter. Results revealed significant interactions between the Niño3.4 region and atmospheric circulation patterns in the Euro-Atlantic region. These interactions involve a combination of well-known patterns such as the NAO, the East Atlantic/West Russia pattern, and the Scandinavian pattern. Second-order ALE plots obtained from a Bayesian neural network highlight that the interplay of these components can drive increasingly warm and wet conditions during late winter. These conditions create a favorable environment for the onset of false spring events, advancing our understanding of the mechanisms behind these impactful phenomena.