| Summary: | Tese de mestrado, Ciências Geofísicas (Meteorologia), Universidade de Lisboa, Faculdade de Ciências, 2009 Average monthly precipitation, the original Palmer Drought Severity Index (PDSI) and a recent adaptation to European soil characteristics, the Self Calibrated PDSI (scPDSI), proposed by Wells (2004), were analysed in this work. Monthly, seasonal and annual trends for these variables were computed for the 1901-2000, 1901-1950 and 1951-2000 periods. These confirm that the majority of the western and central Mediterranean got drier in the last decades of the 20th century while Turkey generally turned wetter (Trigo et al., 2006). An EOF analysis was performed to evaluate the spatio-temporal variability and to reduce the large dimensionality of the fields. EOF1 covers the entire Mediterranean basin (16.4% of explained variance, EV), while EOF2 is dominated by a W-E dipole (10% EV). Smaller scale features found in the following EOF patterns explain smaller amounts of variance. This approach has also contributed to the definition of four sub-regions with large socio-economic relevance: 1) Iberia, 2) Italian Peninsula, 3) Balkans and 4) Turkey. The inter-annual variability of the droughts indices series for each region was analyzed separately. An extreme analysis was applied to the scPDSI, confirming the decline of water supply in most parts of the Mediterranean basin. The impact of main Atlantic sector atmospheric circulation modes in the drought occurrences for different Mediterranean regions was also evaluated. Winter NAO (North Atlantic Oscillation) presents the highest correlations with the winter scPDSI series (above 0.60), and with the following seasons drought conditions. This pattern essentially relates to the available moisture resulting from winter precipitation. Other patterns with relevant links, albeit smaller correlations were found and described. Neste trabalho foram analisados dados de precipitação média mensal, do índice de seca PDSI (Palmer Drought Severity Index) e da sua recente adaptação ...
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