Trends in seasonal surface air temperature in mainland Portugal, since 1941
Article first published online: 8 AUG 2013
© 2013 Royal Meteorological Society
International Journal of Climatology
Volume 34, Issue 6, pages 1814–1837, May 2014
How to Cite
Espírito Santo, F., de Lima, M. I. P., Ramos, A. M. and Trigo, R. M. (2014), Trends in seasonal surface air temperature in mainland Portugal, since 1941. Int. J. Climatol., 34: 1814–1837. doi: 10.1002/joc.3803
- Issue published online: 23 APR 2014
- Article first published online: 8 AUG 2013
- Manuscript Accepted: 8 JUL 2013
- Manuscript Revised: 28 JUN 2013
- Manuscript Received: 21 NOV 2012
- air temperature;
- climate variability;
- modes of low frequency variability;
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.