Seager et al. (2025) Mediterranean Drying by a Positive North Atlantic Oscillation Trend over the Last 65 Years Is an Extreme Outlier in the CMIP6 Multimodel Ensemble

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Climate
• Year: 2025
• Date: 2025-11-26
• Authors: Richard Seager, Haibo Liu, Timothy J. Osborn, Yochanan Kushnir, Jennifer Nakamura, Yutian Wu
• DOI: 10.1175/jcli-d-25-0359.1

Research Groups

Information not provided in the abstract.

Short Summary

The study investigates the causes of observed Mediterranean cool season precipitation decline since the 1950s, finding it to be dynamically driven by a positive North Atlantic Oscillation trend, which current CMIP6 climate models largely fail to reproduce, suggesting either extreme natural variability or a missing forced response.

Objective

• To understand the causes of the observed declining cool season precipitation in the Mediterranean region since the 1950s and to assess how well climate models (CMIP6) reproduce these observed trends and their underlying mechanisms.

Study Configuration

• Spatial Scale: Mediterranean region (central to western, central to eastern), North Atlantic (eastern).
• Temporal Scale: Since the 1950s (multidecadal trends).

Methodology and Data

• Models used: CMIP6 (Coupled Model Intercomparison Project Phase 6) multimodel ensemble.
• Data sources: Observations (precipitation, North Atlantic Oscillation, moisture budget), CMIP6 historical simulations.

Main Results

• The Mediterranean region has experienced a significant decline in cool season precipitation since the 1950s, most pronounced in midwinter and the central to western Mediterranean.
• Observed winter drying in the western Mediterranean is at the extreme edge of the CMIP6 ensemble range, while in the central to eastern Mediterranean, it falls within the lowest percentiles of model distributions.
• Moisture budget analysis reveals the observed drying is dynamic, driven by changes in atmospheric circulation, specifically a positive trend in the North Atlantic Oscillation (NAO) leading to subsiding air and dry northerly advection over the Mediterranean.
• CMIP6 multimodel ensemble shows only modest radiatively forced drying, which is also dynamic but linked to a high-pressure anomaly over the eastern North Atlantic, a pattern distinct from the observed NAO trend.
• A very small number of individual runs from some CMIP6 models do exhibit trends in Mediterranean drying, NAO, and moisture budget similar to observations, but these are rare within the ensemble.
• The observed Mediterranean drying and NAO trends are at the very limit of what climate model simulations can achieve from the combination of internal variability and forced response over this period.

Contributions

• Provides a detailed analysis of the dynamic drivers behind the observed Mediterranean cool season drying, attributing it primarily to a positive trend in the North Atlantic Oscillation.
• Highlights a significant discrepancy between observed Mediterranean drying trends and the majority of CMIP6 model simulations, particularly regarding the underlying atmospheric circulation changes.
• Suggests that the observed drying is either an extremely rare manifestation of natural multidecadal variability not adequately captured by models, or a forced response that current climate models are missing.
• Enhances understanding of the mechanisms driving Mediterranean drying, which is crucial for improving future climate predictions and water resource management in the region.

Funding

Information not provided in the abstract.

Citation

@article{Seager2025Mediterranean,
  author = {Seager, Richard and Liu, Haibo and Osborn, Timothy J. and Kushnir, Yochanan and Nakamura, Jennifer and Wu, Yutian},
  title = {Mediterranean Drying by a Positive North Atlantic Oscillation Trend over the Last 65 Years Is an Extreme Outlier in the CMIP6 Multimodel Ensemble},
  journal = {Journal of Climate},
  year = {2025},
  doi = {10.1175/jcli-d-25-0359.1},
  url = {https://doi.org/10.1175/jcli-d-25-0359.1}
}