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De Lima M.I.P.,University of Coimbra | Espirito Santo F.,IP The Portuguese Sea and Atmosphere Institute | De Lima J.L.M.P.,University of Coimbra | Ramos A.M.,University of Lisbon
Bodenkultur | Year: 2013

This study discusses the climatology of precipitation in mainland Portugal, aiming at the increased understanding of the potential implications of change for the hydrological regimes. It explores trends in selected specific indices that are computed from daily precipitation data of 57 measuring stations across the territory, recorded over 67 years. Results show that precipitation exhibits statistically significant decreasing trends in spring, while extremely heavy precipitation events have become more pronounced in autumn; moreover, results suggest a tendency for a reduction of duration of the rainy season. The expected consequences for the hydrological regimes and for the overall dryness conditions that normally affect large parts of the study area are analysed, especially concerning the hydrology of small basins.

Espirito Santo F.,IP The Portuguese Sea and Atmosphere Institute | De Lima M.I.P.,University of Coimbra | De Lima M.I.P.,Polytechnic Institute of Coimbra | Ramos A.M.,University of Lisbon | Trigo R.M.,University of Lisbon
International Journal of Climatology | Year: 2014

This study provides a thorough assessment of recent changes in near-surface air temperature in mainland Portugal at both the local and regional level, focusing on extreme events (maximum and minimum) at a seasonal scale. It examines trends in selected specific indices that are calculated from daily air temperature data from 23 measuring stations scattered across the territory, recorded between 1941 and 2006. The results show overall warming trends over mainland Portugal that are consistent with the dominant global warming and reflect an increase in both maximum and minimum air temperature. When we split the study period into two sub-periods, 1945-1975 and 1976-2006, the partial trend analysis reveals that the first sub-period is mostly characterized by cooling followed by an even stronger tendency towards warmer benchmarks in all the indices evaluated, in particular for the warm-related temperature extremes in spring and summer. The changes observed in seasonal patterns confirm the well-known asymmetries in the climate in mainland Portugal and suggest that they are likely to be aggravated. There are changes associated with extreme temperatures, in particular, the significant increase in the frequency and duration of heat waves, and the increase in the frequency of hot days and tropical nights, especially in spring and summer; moreover there is a significant decrease in the frequency of cold waves and frost days. Teleconnections associated with changing patterns of temperature are also investigated. The results show that, over mainland Portugal, cold-related air temperature extremes have been associated with the East Atlantic mode in autumn, whereas warm-related extremes have been associated with the Scandinavia teleconnection pattern in spring, summer and autumn. However, the most prominent Northern Hemisphere pattern, the North Atlantic Oscillation, exerts limited influence, which is felt mostly in winter and spring. © 2013 Royal Meteorological Society.

Silva A.,IP The Portuguese Sea and Atmosphere Institute | De Lima M.I.P.,University of Coimbra | Santo F.E.,IP The Portuguese Sea and Atmosphere Institute | Pires V.,IP The Portuguese Sea and Atmosphere Institute
Bodenkultur | Year: 2014

The temporal and spatial variability of precipitation might affect in a different way the society, the environment and the economy at the local and regional scales, depending on specific conditions. This study focuses on using the Standardized Precipitation Index (SPI) to identifying abnormal dry and wet periods and to understanding its spatial patterns at the drainage basin scale, for selected basins in mainland Portugal (1941-2012); this index might be useful in hydrological studies, in particular in basins missing detailed information on precipitation. Overall, SPI shows changes in the extent of dry and wet extremes throughout various time scales that depend on the season and geographical location within mainland Portugal.

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