Piccarreta et al. (2025) Trend analysis of hourly rainfall in the Mediterranean: a case study of the Basilicata Region, Southern Italy (2001–2024)

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-12-12
• Authors: Marco Piccarreta, Mario Bentivenga, Raffaella Piccarreta
• DOI: 10.1007/s00704-025-05939-5

Research Groups

• Ministero della Pubblica Istruzione, Rome, Italy
• Department of Sciences, University of Basilicata, Potenza, Italy
• Department of Decision Sciences, Dondena Centre for Demographic Research, BIDSA - Bocconi University, Milano, Italy

Short Summary

This study analyzed hourly rainfall data (2001–2024) in Basilicata, Southern Italy, revealing a spatially coherent regional signal of increasing frequency and intensity of moderate sub-daily rainfall extremes in summer and autumn, alongside a decline in winter extremes, indicating a seasonal redistribution of precipitation.

Objective

• To examine recent trends in sub-daily rainfall extremes (occurrence, intensity, and spatial variability) across the Basilicata region of southern Italy using high-resolution hourly data from 32 stations.

Study Configuration

• Spatial Scale: Basilicata region, Southern Italy, covering mountainous (47%), hilly (45%), and flatland (8%) areas. Analysis was stratified into four altitudinal ranges: plain (0–100 m), low hill (100–450 m), high hill (450–600 m), and mountain (> 600 m).
• Temporal Scale: 24 years (2001–2024) of hourly rainfall data.

Methodology and Data

• Models used: Mann-Kendall (MK) test, Theil-Sen slope estimator (TSA), Trend-Free Pre-Whitening (TFPW) procedure (for autocorrelation adjustment), Benjamini-Hochberg (BH-FDR) procedure (for multiple testing correction), Holm step-down method, Field Significance Test (FST) (for spatial coherence), Kruskal-Wallis test, and Wilcoxon pairwise comparisons (for physiographic differences).
• Data sources: High-resolution hourly rainfall data from 32 well-distributed automatic electronic stations (with > 95% data availability) operated by the Servizio Agrometeorologico Lucano (SAL).

Main Results

• Initial Mann-Kendall tests detected 99 statistically significant trends, which reduced to 94 after applying the Trend-Free Pre-Whitening (TFPW) procedure to account for serial correlation.
• After rigorous Benjamini-Hochberg False Discovery Rate (BH-FDR) correction for multiple testing, no individual station exhibited statistically significant changes.
• The complementary Field Significance Test (FST) revealed spatially coherent regional signals for four indices: Fp950summer, Fp990summer, Rx3hrwinter, and Rx3hr20winter, indicating summer intensification and winter decline of certain extreme rainfall characteristics.
• Moderate extremes (95th percentile) showed widespread upward tendencies in both frequency and intensity, particularly in summer and autumn, with over 80% of stations showing positive trends (e.g., mean slopes of +2.4 mm for Fp950Ann and +0.23 events/yr for Rp950Ann).
• The most severe events (99th – 99.9th percentiles) remained statistically stationary, showing no significant changes.
• Kruskal-Wallis and post-hoc Wilcoxon tests indicated statistically significant differences in rainfall extreme magnitudes and frequencies among physiographic zones, with mountainous and high-hilly sectors exhibiting stronger trends and higher values of short-duration extremes compared to lowlands.

Contributions

• Provides the first regional-scale synthesis of trends in sub-daily extreme rainfall for the Basilicata region, Southern Italy.
• Introduces an integrated statistical framework combining multiple approaches (trend detection, serial correlation adjustment, multiple testing correction, spatial coherence testing, and physiographic stratification) to robustly distinguish genuine climatic signals from natural variability.
• Offers valuable insights and a replicable model for hydrological risk assessment and climate adaptation planning in other Mediterranean "hot spot" regions.

Funding

Not applicable.

Citation

@article{Piccarreta2025Trend,
  author = {Piccarreta, Marco and Bentivenga, Mario and Piccarreta, Raffaella},
  title = {Trend analysis of hourly rainfall in the Mediterranean: a case study of the Basilicata Region, Southern Italy (2001–2024)},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05939-5},
  url = {https://doi.org/10.1007/s00704-025-05939-5}
}