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<p>In this study, we report a thermodynamic paradox in southwestern Europe: a significant increase in rainfall extremes coexisting with a systematic decline in ordinary rainfall. Using non-negative matrix factorization (NNMF) applied to precipitation data from high-density stations (1950–2024) and the ERA5 reanalysis, we demonstrate that the region has entered a regime of asymmetric redistribution, wherein the intensification of extreme events is accompanied by a concurrent erosion of ordinary precipitation. Furthermore, non-stationary correlation analysis reveals a recent dynamic decoupling: while Atlantic-influenced regions remain dynamically driven by frontal systems, Mediterranean extremes have lost their historical association with large-scale synoptic patterns, confirming a fundamentally thermodynamically amplified regime. Ultimately, this transforms a region of Atlantic influence into a hot spot of hydroclimatic volatility. A profound temporal decoupling emerges between reanalysis precipitation variables and observations, revealing a critical saturation-efficiency gap: the atmosphere produces fewer ordinary rainfall events, yet produces extremes with unprecedented energetic magnitude, transforming a region of Atlantic influence into a hot spot of hydroclimatic volatility.</p> Graphical Abstract <p></p> <p>This research characterizes the structural transformation of the hydrological regime in Southwest Europe from 1950 to 2024. The study uses a high-density observational data network of 8,207 weather stations across mainland Spain and the Balearic Islands, AEMET ROCIO grid precipitation data, and integrated ERA5 reanalysis atmospheric variables. The analyses employ Non-Negative Matrix Factorization (NNMF) to regionalize precipitation into four distinct modes (Cantabrian, Southwest, Mediterranean, and Interior) and apply change-point detection algorithms to identify regime shifts. The model focuses on the “thermodynamic efficiency gap,” analyzing how variables such as Total Column Water Vapor (TCWV) and Relative Humidity (RH) drive rainfall trends. Key results reveal a systemic asymmetric redistribution of precipitation: while ordinary precipitation (Ro) exhibits a widespread decline due to decreasing relative humidity, absolute extreme events (Rp95) are intensifying. Since 1950, total atmospheric water vapor (TCWV) has increased by ~ 9%, reaching record anomalies of + 1.6σ after 2010, yet the concurrent drop in RH hinders ordinary saturation. Furthermore, a marked seasonal dual nature is uncovered: the intensification of absolute extremes is driven by spring (MAM) in the Levante region and by autumn (SON) in the Southwest, with physical support from seasonal moisture supply (IVT). The study concludes that the region has transitioned into a highly intensified hydro-climatic regime. The atmosphere suppresses ordinary rain through drying, while accumulating unprecedented thermodynamic potential that is discharged during severe frontal events. These findings highlight a critical discrepancy in current reanalysis models (which fail to capture localized convective intensification) and necessitate a fundamental recalibration of water management and flood-risk strategies.</p>

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Asymmetric Precipitation Redistribution: The Thermodynamic Decoupling of Extremes in Southwest Europe

  • 期刊论文

  • 发表日期：

    2026年6月29日

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  • Eduardo A. Agosta,
  • David Corell,
  • Juan J. Miró,
  • María José Estrela

摘要

In this study, we report a thermodynamic paradox in southwestern Europe: a significant increase in rainfall extremes coexisting with a systematic decline in ordinary rainfall. Using non-negative matrix factorization (NNMF) applied to precipitation data from high-density stations (1950–2024) and the ERA5 reanalysis, we demonstrate that the region has entered a regime of asymmetric redistribution, wherein the intensification of extreme events is accompanied by a concurrent erosion of ordinary precipitation. Furthermore, non-stationary correlation analysis reveals a recent dynamic decoupling: while Atlantic-influenced regions remain dynamically driven by frontal systems, Mediterranean extremes have lost their historical association with large-scale synoptic patterns, confirming a fundamentally thermodynamically amplified regime. Ultimately, this transforms a region of Atlantic influence into a hot spot of hydroclimatic volatility. A profound temporal decoupling emerges between reanalysis precipitation variables and observations, revealing a critical saturation-efficiency gap: the atmosphere produces fewer ordinary rainfall events, yet produces extremes with unprecedented energetic magnitude, transforming a region of Atlantic influence into a hot spot of hydroclimatic volatility.

Graphical Abstract

This research characterizes the structural transformation of the hydrological regime in Southwest Europe from 1950 to 2024. The study uses a high-density observational data network of 8,207 weather stations across mainland Spain and the Balearic Islands, AEMET ROCIO grid precipitation data, and integrated ERA5 reanalysis atmospheric variables. The analyses employ Non-Negative Matrix Factorization (NNMF) to regionalize precipitation into four distinct modes (Cantabrian, Southwest, Mediterranean, and Interior) and apply change-point detection algorithms to identify regime shifts. The model focuses on the “thermodynamic efficiency gap,” analyzing how variables such as Total Column Water Vapor (TCWV) and Relative Humidity (RH) drive rainfall trends. Key results reveal a systemic asymmetric redistribution of precipitation: while ordinary precipitation (Ro) exhibits a widespread decline due to decreasing relative humidity, absolute extreme events (Rp95) are intensifying. Since 1950, total atmospheric water vapor (TCWV) has increased by ~ 9%, reaching record anomalies of + 1.6σ after 2010, yet the concurrent drop in RH hinders ordinary saturation. Furthermore, a marked seasonal dual nature is uncovered: the intensification of absolute extremes is driven by spring (MAM) in the Levante region and by autumn (SON) in the Southwest, with physical support from seasonal moisture supply (IVT). The study concludes that the region has transitioned into a highly intensified hydro-climatic regime. The atmosphere suppresses ordinary rain through drying, while accumulating unprecedented thermodynamic potential that is discharged during severe frontal events. These findings highlight a critical discrepancy in current reanalysis models (which fail to capture localized convective intensification) and necessitate a fundamental recalibration of water management and flood-risk strategies.