Silva et al. (2025) Rainfall Patterns and Trends on São Miguel Island (Azores, Portugal): A Hierarchical Clustering and Trend Analysis Approach

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

Identification

• Journal: Climate
• Year: 2025
• Date: 2025-11-20
• Authors: Rui Fagundes Silva, Rui Marques, José Luı́s Zêzere, Marcelo Fragoso
• DOI: 10.3390/cli13110238

Research Groups

Not provided in the text.

Short Summary

This study identified four distinct rainfall clusters on São Miguel Island, revealing a strong altitude-rainfall correlation but also significant recent declines in annual and seasonal rainfall, particularly in autumn and winter, which may deviate from global climate change model projections.

Objective

• To address rainfall patterns and trends on São Miguel Island (Azores, Portugal).

Study Configuration

• Spatial Scale: São Miguel Island (Azores, Portugal).
• Temporal Scale: Climatological periods of 1978/79–2019/20 (full dataset), 1978/79–2009/10 (oldest sub-dataset), and 2010/11–2019/20 (latest sub-dataset).

Methodology and Data

• Models used: Ward’s hierarchical clustering method, Mann–Kendall test, Sen’s slope test.
• Data sources: Monthly rainfall data from 21 rainfall stations.

Main Results

• Four homogeneous rainfall clusters were identified across São Miguel Island.
• Mean Annual Rainfall (MAP) ranged from 835.8 mm in low-altitude areas to 2925.5 mm in high-elevation regions.
• A strong correlation (R² up to 0.83) was found between altitude and rainfall, indicating an increase of approximately 196 mm of MAP per 100 m elevation gain.
• No notable variation in rainfall was observed between the island’s windward and leeward slopes.
• Significant declines in both annual and seasonal rainfall were detected in recent years.
• The strongest decreases occurred in autumn and winter, with trends as steep as −31.6 mm/year and −12.1 mm/year in autumn (Fogo III station).
• Between the oldest and most recent periods, rainfall reductions reached up to 41% in autumn (P10) and 55% in winter (P10), primarily affecting clusters at lower and mid-altitudes.
• The overall rainfall trend hints at a potential deviation from projections of global climate change models and previous long-term rainfall studies.
• The predominantly positive phase of the North Atlantic Oscillation (NAO) in recent years likely contributed to the observed decrease in rainfall.

Contributions

• Provides a refined spatial and temporal characterisation of rainfall across São Miguel Island.
• Improves the understanding of local climatic variability in the Azores.
• Offers valuable insights for regional water management and climate adaptation strategies.

Funding

Not provided in the text.

Citation

@article{Silva2025Rainfall,
  author = {Silva, Rui Fagundes and Marques, Rui and Zêzere, José Luı́s and Fragoso, Marcelo},
  title = {Rainfall Patterns and Trends on São Miguel Island (Azores, Portugal): A Hierarchical Clustering and Trend Analysis Approach},
  journal = {Climate},
  year = {2025},
  doi = {10.3390/cli13110238},
  url = {https://doi.org/10.3390/cli13110238}
}