Nunno et al. (2026) Teleconnection-informed clustering of temporally compound hydroclimatic extremes in Europe: post-drought extreme rainfall probability and long-term trends

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-03-27
• Authors: Fabio Di Nunno, Mehmet Berkant Yıldız, Francesco Granata
• DOI: 10.1007/s00382-026-08150-y

Research Groups

• Department of Civil and Mechanical Engineering (DICEM), University of Cassino and Southern Lazio, Cassino, Frosinone, Italy

Short Summary

This study analyzed compound drought-rainfall extremes across Europe (1976–2023) using teleconnection-informed clustering, revealing three distinct hydroclimatic regimes where post-drought extreme rainfall probabilities are heterogeneous and strongly modulated by large-scale atmospheric circulation. The findings indicate that extreme rainfall can occur during or after drought without necessarily ending the drought, emphasizing the critical role of atmospheric teleconnections.

Objective

• To develop a comprehensive, data-driven framework to investigate compound drought–extreme rainfall dynamics across Europe, specifically quantifying the probability of extreme rainfall events following drought conditions and identifying teleconnection-informed hydroclimatic regimes.

Study Configuration

• Spatial Scale: European continent, with SPEI-3 data at 0.5° × 0.5° resolution and daily rainfall observations from 430 stations selected using a 1° × 1° spatial filtering grid.
• Temporal Scale: January 1976–December 2023. Post-drought rainfall responses were evaluated across six consecutive, non-overlapping two-month windows (0–2, 2–4, 4–6, 6–8, 8–10, and 10–12 months) after drought termination.

Methodology and Data

• Models used: K-means, Hierarchical clustering, Black Hole Clustering (BHC), Spectral Bridges (SB) for hydroclimatic clustering. Decision tree models for feature importance analysis. Seasonal Kendall (SK) test for trend detection.
• Data sources:
  • Drought conditions: Standardized Precipitation–Evapotranspiration Index (SPEI-3) from the SPEI Global Drought Monitor.
  • Daily precipitation: Quality-controlled station records from the European Climate Assessment & Dataset (ECA&D).
  • Teleconnection indices: Arctic Oscillation (AO), Greenland Blocking Index (GBI), Mediterranean Oscillation Index (Algiers and Cairo; MOI AC ), Scandinavian Pattern (SCAND), and Western Mediterranean Oscillation (WeMO) from NOAA PSL and CRU data.

Main Results

• Three coherent hydroclimatic regimes were identified across Europe, with the Spectral Bridges (SB) algorithm producing the most spatially coherent and interpretable classification.
• Northern Europe (Cluster 1): Extreme rainfall probability peaks at 10% within 2–4 months post-drought. This region shows a statistically significant positive trend in mean rainfall (Z = 2.99) but a persistent and statistically significant negative trend in SPEI-3 (Z = − 5.14), indicating increasing drought severity despite higher rainfall.
• Southern Europe (Cluster 2): Exhibits stronger and more persistent extreme rainfall, rising from 2% during drought to a peak of 14% within 8–10 months post-drought. SPEI-3 trends remain statistically significantly negative (Z = − 5.15), while mean rainfall trends are non-significant (Z = 0.55).
• Central Europe (Cluster 3): Shows the most delayed extreme rainfall probability peak (13% at 10–12 months post-drought). This cluster exhibits the strongest statistically significant negative SPEI-3 trends (Z = − 6.26), with non-significant positive mean rainfall trends (Z = 1.21).
• Feature importance analysis revealed that correlations between SPEI-3/rainfall and teleconnection indices (particularly Arctic Oscillation and Mediterranean Oscillation) are the most influential predictors for cluster assignment, highlighting the dominant role of large-scale atmospheric circulation.
• The study demonstrates that extreme rainfall can occur during or after drought conditions without necessarily implying drought termination.

Contributions

• Provides a novel, teleconnection-aware framework for classifying compound drought–extreme rainfall dynamics across Europe, integrating conditional probabilities, advanced clustering, and trend analysis.
• Identifies and characterizes three distinct, physically consistent hydroclimatic regimes across Europe based on post-drought extreme rainfall probabilities and teleconnection influences, offering a more nuanced understanding than traditional geographical divisions.
• Quantifies the spatially and temporally heterogeneous nature of post-drought extreme rainfall responses, showing early peaks in northern Europe and delayed, amplified responses in southern and central regions.
• Emphasizes the critical role of large-scale atmospheric circulation (teleconnections) in modulating regional hydroclimatic variability and shaping compound extreme events.
• Offers direct implications for region-specific flood risk management, water planning, and climate adaptation strategies by providing quantitative insights into evolving drought–rainfall linkages.

Funding

• The authors declare no relevant financial or non-financial interests to disclose and no specific projects or programs are listed as funding this research.

Citation

@article{Nunno2026Teleconnectioninformed,
  author = {Nunno, Fabio Di and Yıldız, Mehmet Berkant and Granata, Francesco},
  title = {Teleconnection-informed clustering of temporally compound hydroclimatic extremes in Europe: post-drought extreme rainfall probability and long-term trends},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-026-08150-y},
  url = {https://doi.org/10.1007/s00382-026-08150-y}
}