Pereira et al. (2019) Extreme precipitation events under climate change in the Iberian Peninsula

Identification

• Journal: International Journal of Climatology
• Year: 2019
• Date: 2019-08-07
• Authors: Susana Cardoso Pereira, Martinho Marta‐Almeida, Ana Cristina Carvalho, Alfredo Rocha
• DOI: 10.1002/joc.6269

Research Groups

• Department of Earth Sciences, University of Florence, Italy
• Department of Earth Sciences, University of Pisa, Italy
• Istituto Nazionale di Geofísica e Vulcanologia (INGV), Roma, Italy
• CIRSEC Centro Interdipartimentale di Ricerca per lo Studio degli Effetti del Cambiamento Climatico dell’Università di Pisa, Italy
• Department of Civil and Industrial Engineering, University of Pisa, Italy
• Institute of Geosciences and Earth Resources, IGG-CNR, Pisa, Italy
• Istituto di Geologia Ambientale e Geoingegneria, IGAG-CNR, Rome, Italy

Short Summary

This study investigates seasonal rainfall trends in Tuscany, Italy, over 70 years (1950-2020) by correlating them with large-scale atmospheric circulation patterns (NAO, EA, WeMO) and sea surface temperatures, revealing a significant decrease in summer rainfall attributed to global warming-induced sea surface temperature increases.

Objective

• To understand the seasonal rainfall trends in Tuscany, Italy, over the last 70 years (1950-2020) in relation to large-scale atmospheric circulation patterns (North Atlantic Oscillation, East Atlantic, Western Mediterranean Oscillation) and sea surface temperatures.
• To evaluate the effectiveness of linear models compared to traditional statistical correlations in explaining the relationship between climate patterns and seasonal rainfall.

Study Configuration

• Spatial Scale: Tuscany, Italy, a region in the northern Mediterranean (0°N-65°N, 80°W-0°E for NASST; 38°N-49°N, 0°E-28°E for MSST; 42.8°N-44.8°N, 7.6°E-10.76°E for GGSST), characterized by mean annual precipitation ranging from 400 to 3000 mm per year.
• Temporal Scale: 70 years, from 1950 to 2020, analyzed seasonally (December-January-February, March-April-May, June-July-August, September-October-November).

Methodology and Data

• Models used:
  • Spearman's correlation coefficient (SCC) for statistical correlation.
  • Linear models (Rp = αNAO + βWeMO + γEA + δ) to predict rainfall anomalies.
  • Detrended Cross-Correlation Analysis (DCCA) to verify the influence of trends on SCC results.
• Data sources:
  • Rainfall: 117 time series from 1103 raingauges in Tuscany, Italy, provided by the Tuscany Region Hydrologic Service (SIR) network (daily data, 1950-2020). Data were processed into Percentage Anomalies of Rainfall (PAR) relative to the 1961-1990 mean, and smoothed with a 10-year mobile window (Mean Average PAR, MAPAR).
  • North Atlantic Oscillation (NAO): PC-based index from the US National Center for Atmospheric Research (NCAR) (monthly frequency, January 1889-December 2020).
  • East Atlantic (EA): Index from the National Weather Service of NOAA (monthly frequency, 1950-2020), standardized by 1981-2010 climatology.
  • Western Mediterranean Oscillation (WeMO): Index from the Climatic Research Unit (CRU) of the University of East Anglia (monthly frequency, starts 1821).
  • Sea Surface Temperature (SST): Extended Reconstructed Sea Surface Temperature (ERSST) dataset version 5 (NOAA, 2021), expressed as 10-year mobile window anomalies relative to the 1961-1990 mean. Specific areas for Northern Atlantic SST (NASST), Mediterranean SST (MSST), and Genoa Gulf SST (GGSST) were defined.

Main Results

• Summer (June-July-August) rainfall in Tuscany shows a clear progressive reduction of up to 30% from 1965 to 2005, with a slight increase in recent years, primarily linked to a negative phase of the East Atlantic index.
• Winter (December-January-February) rainfall experienced a significant reduction of 30-40% between 1984 and 2005, followed by a progressive increase from 2005 to 2020. This period was marked by positive NAO and EA phases and a negative WeMO phase, with a shift in the main climatic driver after 2005.
• Spring (March-April-May) rainfall decreased between 1985 and 2008, characterized by a persistent negative WeMO phase and positive NAO and EA phases.
• Autumn (September-October-November) rainfall shows high variability with two wet periods (around 1965 and 1995) and two dry periods (1970-1990), with NAO identified as the strongest driver in linear models, correlating with negative phases.
• Sea Surface Temperatures (NASST, MSST, GGSST) exhibit a clear increasing trend since the 1980s across all seasons, with the most pronounced increase observed during summer.
• Linear models provided more plausible and detailed insights into the influence of atmospheric patterns on rainfall, especially for the autumn season, compared to traditional Spearman's correlation coefficients.

Contributions

• Introduction and validation of linear models as an innovative and effective method to clarify the individual role and influence of large-scale atmospheric circulation patterns on seasonal rainfall, offering more detailed insights than traditional statistical correlations.
• Comprehensive analysis of 70-year seasonal rainfall trends in Tuscany, Italy, a critical Mediterranean hotspot, linking them directly to the dynamics of NAO, EA, WeMO, and regional sea surface temperature variations.
• Elucidation of how current global warming, through increased sea surface temperatures, contributes to reduced water availability in the Mediterranean, particularly in warm seasons, by influencing atmospheric circulation patterns and subsequently decreasing precipitation.

Funding

• Project no. 249792 “Dalla Preistoria all'Antropocene: Nuove Tecnologie per la valorizzazione dell'eredità culturale della Versilia (PANTAREI)” Tuscany Region (call POR FSE 2014-2020)
• Collaborative research agreement no. 579999-2019 “Autorità di Bacino Distrettuale Appennino Settentrionale”
• Project: “Cambiamenti globali e impatti locali: conoscenza e consapevolezza per uno sviluppo sostenibile della pianura Apuo-versiliese” Fondazione Cassa Risparmio di Lucca

Citation

@article{Pereira2019Extreme,
  author = {Pereira, Susana Cardoso and Marta‐Almeida, Martinho and Carvalho, Ana Cristina and Rocha, Alfredo},
  title = {Extreme precipitation events under climate change in the Iberian Peninsula},
  journal = {International Journal of Climatology},
  year = {2019},
  doi = {10.1002/joc.6269},
  url = {https://doi.org/10.1002/joc.6269}
}