Río et al. (2010) Spatial distribution of recent rainfall trends in Spain (1961–2006)

Identification

• Journal: International Journal of Climatology
• Year: 2010
• Date: 2010-03-01
• Authors: Sara del Río, Luis Herrero, Roberto Fraile, Ángel Penas
• DOI: 10.1002/joc.2111

Research Groups

• Institute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland
• Oeschger Centre for Climate Change Research (OCCR), University of Bern, Bern, Switzerland
• Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), Rome, Italy
• The Cyprus Institute, EEWRC, Nicosia, Cyprus
• Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus-Liebig University of Giessen, Giessen, Germany

Short Summary

This study characterizes daily extreme winter precipitation events at 20 Mediterranean coastal sites from 1950-2006 using Extreme Value Theory, revealing their significant contribution to seasonal totals and identifying associated large-scale atmospheric circulation patterns. The findings enhance the understanding of cold season precipitation extremes and their atmospheric drivers in the Mediterranean.

Objective

• To characterize daily extreme precipitation events during the extended winter season (October–March) at 20 Mediterranean coastal sites and to investigate their relationship with large-scale anomalous atmospheric circulation patterns.

Study Configuration

• Spatial Scale: 20 Mediterranean coastal stations. Atmospheric reanalysis data covered the area from 25°N to 65°N and 35°W to 52°E.
• Temporal Scale: Daily precipitation data for the extended winter season (October–March) from 1950–2006. Daily NCEP/NCAR reanalysis data for the same period.

Methodology and Data

• Models used:
  • Declustered Peak Over Threshold (dePOT) model based on the Generalized Pareto Distribution (GPD) for extreme value analysis.
  • Minimum Density Power Divergence Estimator (MDPDE) for GPD parameter estimation.
  • Goodness-of-fit approach (Cramér-von Mises and Anderson-Darling statistics) for objective threshold selection.
  • Ferro and Segers (2003) objective procedure for declustering and extremal index estimation.
  • Poisson regression for analyzing trends in exceedance occurrences.
  • A 2-step classification procedure for atmospheric patterns: Self-Organizing Map (SOM) for protocluster identification, followed by a Genetic k-means algorithm (GK).
  • T-mode Principal Component Analysis (PCA) with a dimensionality test for objectively determining the optimal number of clusters.
  • Nonparametric Brunner-Munzel test for assessing the significance of atmospheric anomaly patterns.
• Data sources:
  • Daily precipitation series from 20 coastal stations across the Mediterranean, collected within the EU-FP6 project CIRCE.
  • Daily NCEP/NCAR reanalysis data for mid-tropospheric geopotential height at 500 hPa (Z500), Sea Level Pressure (SLP), and wind intensity (u and v components) at 250 hPa.

Main Results

• Extreme precipitation events contribute approximately 60% to the total extended winter season precipitation across all analyzed stations.
• Estimated 5-year return levels for daily extreme precipitation range from 58 mm to 150 mm, with Genoa (Italy) showing the highest value.
• Estimated 50-year return levels range from 82 mm to 264 mm, with Genoa (Italy) again having the highest value (264 mm). Alicante (Spain) also showed a high 50-year return level of 200 mm, indicating significant flood risk.
• Six stations (Amiantos, Marseille, Rhodes, Argostoli, Genoa, Teramo) exhibited a significant negative trend in the probability of observing an extreme event over the 57-year period.
• Eight stations showed a significant negative trend in seasonal total precipitation, with Argostoli (Greece) having the highest decrease of -8.4 ± 1.97 mm/year.
• Three significant atmospheric anomaly patterns for Z500 and SLP were identified for both the western and eastern Mediterranean basins, which were statistically distinct from patterns associated with dry and non-extreme wet days.
• In the western Mediterranean, extreme events are linked to anomalous southwesterly surface to mid-tropospheric flow, enhanced moisture transport from the Atlantic, and an interaction between the subtropical and eddy-driven jet streams.
• In the eastern Mediterranean, extreme events are associated with warm air advection, anomalous ascent motions, increased low- to mid-tropospheric moisture, and the jet stream position favoring a divergence area.

Contributions

• Provided a robust characterization of daily extreme winter precipitation events in the Mediterranean using advanced Extreme Value Theory techniques, including objective parameter estimation, declustering, and threshold selection, offering more reliable results and confidence intervals than traditional index-based methods.
• Developed and applied a novel 2-step classification procedure (SOM, Genetic k-means, and PCA-based dimensionality test) for objectively identifying and characterizing large-scale atmospheric circulation patterns associated with extreme precipitation.
• Offered detailed insights into the physical mechanisms driving extreme precipitation events in the Mediterranean, including the role of moisture transport, ascending motions, and the interaction and positioning of the subtropical and polar jet streams.
• Contributed to a better understanding of the spatial and temporal variability of extreme precipitation in a climate change "hot-spot" region, which is crucial for climate risk management.

Funding

• EU/FP6 integrated project CIRCE (Climate Change and Impact Research: the Mediterranean Environment; contract number 036961)
• EU/FP7 project ACQWA (Assessing Climate Impacts on the Quantity and Quality of Water; grant 212250)
• MedClivar

Citation

@article{Río2010Spatial,
  author = {Río, Sara del and Herrero, Luis and Fraile, Roberto and Penas, Ángel},
  title = {Spatial distribution of recent rainfall trends in Spain (1961–2006)},
  journal = {International Journal of Climatology},
  year = {2010},
  doi = {10.1002/joc.2111},
  url = {https://doi.org/10.1002/joc.2111}
}