Sonny et al. (2026) Hydrological drought projections across Europe under climate change

Identification

• Journal: npj natural hazards.
• Year: 2026
• Date: 2026-03-26
• Authors: Fatimatuj Zohara Sonny, Sogol Moradian, Agnieszka I. Olbert
• DOI: 10.1038/s44304-025-00152-w

Research Groups

• Department of Civil Engineering, College of Science and Engineering, University of Galway, Galway, Ireland
• Department of Civil Engineering and Construction, Atlantic Technological University, Sligo, Ireland

Short Summary

This study comprehensively assesses future hydrological drought dynamics across Europe using the Standardized Runoff Index (SRI) under two climate change scenarios, revealing an intensification of drought conditions, particularly in southern Europe, with spring identified as the most drought-prone season. The findings project significant increases in drought frequency, severity, and spatial extent, necessitating urgent, seasonally adaptive water management strategies.

Objective

• To quantify the severity, duration, and frequency of hydrological droughts and to identify long-term spatial and temporal patterns across Europe under the impacts of climate change.

Study Configuration

• Spatial Scale: Continental Europe, approximately 10.53 million square kilometers, stretching from 35°N to 71°N latitude and from 25°W to 40°E longitude.
• Temporal Scale: Historical period (1990–2014) and near-future period (2015–2049), with specific analyses for 2005–2014 and 2040–2049. SRI calculated at 1-month and 3-month timescales.

Methodology and Data

• Models used: Ensemble mean of 13 General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6).
• Data sources:
  • Surface runoff (mrros) data from CMIP6 under two Shared Socioeconomic Pathways (SSPs): SSP1-2.6 (low-emission) and SSP5-8.5 (high-emission).
  • ERA5-Land reanalysis (0.1° spatial resolution, approximately 9 km) for daily accumulated surface runoff (1990–2014) used as observational benchmark.
  • Standardized Runoff Index (SRI) calculated using a non-parametric method (Gringorten formula) from bias-corrected runoff data.
  • Bias correction: Quantile Mapping (QM) method applied to CMIP6 ensemble mean runoff data.
  • Statistical analysis: Wilcoxon signed-rank test, Mann–Whitney U test, and Mann–Kendall trend test (p < 0.05 significance threshold).

Main Results

• Bias correction significantly improved model performance, reducing errors (MAE, MBE, RMSE) and improving accuracy (PBIAS).
• Seasonal surface runoff is projected to generally decline across Europe, with the most significant reductions in winter under SSP1-2.6 (from 0.21 to 0.19 cubic meters per second) and spring under SSP5-8.5 (from 0.38 to 0.28 cubic meters per second).
• Autumn surface runoff shows an increase under SSP5-8.5 (from 0.23 to 0.27 cubic meters per second), indicating a temporal redistribution.
• Spring is consistently identified as the most drought-prone season, with mean SRI declining to -0.45 under SSP5-8.5 (compared to -0.30 historically).
• A statistically significant upward trend in drought-affected land area is projected from 2015 to 2049, increasing by 0.23% per year under SSP1-2.6 and 0.21% per year under SSP5-8.5.
• Moderate, severe, and extreme drought conditions are projected to increase over time, particularly during 2035–2049. For example, in spring 2048 under SSP5-8.5, 39.30% of Europe is projected to be in drought, with 10.12% experiencing extreme drought.
• Drought hotspots, characterized by increased frequency, duration, severity, and intensity, include southern and southeastern Europe (e.g., France, Spain, Balkans, Italy, Turkey, Greece, Iberian Peninsula) and parts of northern Europe (e.g., Finland, Sweden, UK).
• Long-term SRI trends indicate widespread drying, with negative trends observed in 96% of grid cells under SSP1-2.6 and 83% under SSP5-8.5.
• A clear north-south gradient in drought evolution is observed, with northern and western Europe potentially experiencing stable or slightly wetter conditions, while Mediterranean regions face further aridification.

Contributions

• Provides a comprehensive, high-resolution assessment of future hydrological drought dynamics across Europe, specifically focusing on runoff-specific trends using the Standardized Runoff Index (SRI).
• Delivers bias-corrected projections of future drought risk based on an ensemble of CMIP6 models under two contrasting emission scenarios (SSP1-2.6 and SSP5-8.5).
• Quantifies key drought characteristics (severity, duration, frequency, intensity) and identifies long-term spatial and temporal patterns, offering insights crucial for water resource management.
• Highlights spring as the most critical season for water scarcity across Europe, emphasizing the need for seasonally informed adaptation strategies.
• Enhances the reliability of future drought projections by integrating multiple datasets, applying robust bias correction, and employing appropriate statistical methods.

Funding

• This research was supported by the College of Science and Engineering, University of Galway, Galway, Ireland.

Citation

@article{Sonny2026Hydrological,
  author = {Sonny, Fatimatuj Zohara and Moradian, Sogol and Olbert, Agnieszka I.},
  title = {Hydrological drought projections across Europe under climate change},
  journal = {npj natural hazards.},
  year = {2026},
  doi = {10.1038/s44304-025-00152-w},
  url = {https://doi.org/10.1038/s44304-025-00152-w}
}