Structural changes in the interannual variability of extreme autumn precipitation in eastern Spain and the weakening of synoptic forcing

Abstract This study analyzes the evolution of autumn precipitation on the Mediterranean side of the Iberian Peninsula (Levante) and the spatiotemporal variations in its atmospheric forcings in 1950–2024. Using a dense network of observational data and the ERA5 reanalysis, a seasonal rainfall redistribution process is identified, marked by a statistically significant structural break in 1981. In the recent subperiod, extreme precipitation ( R p95 ) increases at the expense of ordinary precipitation ( R o ), while the total seasonal volume remains stationary. A decoupling of R p95 from key atmospheric indices, such as the Western Mediterranean Oscillation (WeMO) and blocking patterns, is detected. Although the seasonal synoptic‐trigger frequency remains strictly stationary, daily‐scale analysis demonstrates a 31% surge in the absolute rate of local extreme events, revealing a profound shift in thermodynamic efficiency. Composite differences show current torrential events occur in a dynamically more restrictive environment, characterized by an expanded subtropical ridge and subsidence anomalies in the middle troposphere. This attenuation of large‐scale dynamic forcing is offset by a highly localized thermodynamic increase in base specific humidity (up to +0.52 g·kg −1 ), confined to the planetary boundary layer, and amplified latent instability (Convective Available Potential Energy, CAPE), and mechanically capped by the background subsidence (Convective Inhibition, CIN). The Reynolds decomposition of moisture flux confirms a dynamic restructuring. The anomalous transport of the mean circulation loses statistical significance in the Levante and is replaced by low‐frequency flows conditioned by the orography, highlighting a bifurcation effect by the Pyrenees and intense channeling through the Ebro Valley. Transient high‐frequency eddies reveal a pattern of surface divergence over the Balearic Sea that accelerates intense maritime flows toward the coast. Upon impacting the Levantine coastline, these flows generate a deep anomalous convergence that overcomes the background inhibition. Thus, in an environment of synoptic subsidence and enriched moisture, torrential convective activity is driven by forced orographic lifting.